* [PATCH v2 1/7] mm, swap: avoid reclaiming irrelevant swap cache
2025-02-24 18:02 [PATCH v2 0/7] mm, swap: remove swap slot cache Kairui Song
@ 2025-02-24 18:02 ` Kairui Song
2025-02-24 18:02 ` [PATCH v2 2/7] mm, swap: drop the flag TTRS_DIRECT Kairui Song
` (5 subsequent siblings)
6 siblings, 0 replies; 14+ messages in thread
From: Kairui Song @ 2025-02-24 18:02 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Chris Li, Barry Song, Hugh Dickins, Yosry Ahmed,
Huang, Ying, Baoquan He, Nhat Pham, Johannes Weiner, Baolin Wang,
Kalesh Singh, Matthew Wilcox, linux-kernel, Kairui Song
From: Kairui Song <kasong@tencent.com>
Swap allocator will do swap cache reclaim to recycle HAS_CACHE slots for
allocation. It initiates the reclaim from the offset to be reclaimed and
looks up the corresponding folio. The lookup process is lockless, so it's
possible the folio will be removed from the swap cache and given
a different swap entry before the reclaim locks the folio. If
it happens, the reclaim will end up reclaiming an irrelevant folio, and
return wrong return value.
This shouldn't cause any problem with correctness or stability, but
it is indeed confusing and unexpected, and will increase fragmentation,
decrease performance.
Fix this by checking whether the folio is still pointing to the offset
the allocator want to reclaim before reclaiming it.
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
---
mm/swapfile.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index a7f60006c52c..5618cd1c4b03 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -210,6 +210,7 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
int ret, nr_pages;
bool need_reclaim;
+again:
folio = filemap_get_folio(address_space, swap_cache_index(entry));
if (IS_ERR(folio))
return 0;
@@ -227,8 +228,16 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
if (!folio_trylock(folio))
goto out;
- /* offset could point to the middle of a large folio */
+ /*
+ * Offset could point to the middle of a large folio, or folio
+ * may no longer point to the expected offset before it's locked.
+ */
entry = folio->swap;
+ if (offset < swp_offset(entry) || offset >= swp_offset(entry) + nr_pages) {
+ folio_unlock(folio);
+ folio_put(folio);
+ goto again;
+ }
offset = swp_offset(entry);
need_reclaim = ((flags & TTRS_ANYWAY) ||
--
2.48.1
^ permalink raw reply [flat|nested] 14+ messages in thread* [PATCH v2 2/7] mm, swap: drop the flag TTRS_DIRECT
2025-02-24 18:02 [PATCH v2 0/7] mm, swap: remove swap slot cache Kairui Song
2025-02-24 18:02 ` [PATCH v2 1/7] mm, swap: avoid reclaiming irrelevant swap cache Kairui Song
@ 2025-02-24 18:02 ` Kairui Song
2025-02-24 18:02 ` [PATCH v2 3/7] mm, swap: avoid redundant swap device pinning Kairui Song
` (4 subsequent siblings)
6 siblings, 0 replies; 14+ messages in thread
From: Kairui Song @ 2025-02-24 18:02 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Chris Li, Barry Song, Hugh Dickins, Yosry Ahmed,
Huang, Ying, Baoquan He, Nhat Pham, Johannes Weiner, Baolin Wang,
Kalesh Singh, Matthew Wilcox, linux-kernel, Kairui Song
From: Kairui Song <kasong@tencent.com>
This flag exists temporarily to allow the allocator to bypass the slot
cache during freeing, so reclaiming one slot will free the slot
immediately.
But now we have already removed slot cache usage on freeing, so this
flag has no effect now.
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
---
mm/swapfile.c | 23 +++--------------------
1 file changed, 3 insertions(+), 20 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5618cd1c4b03..6f2de59c6355 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -158,8 +158,6 @@ static long swap_usage_in_pages(struct swap_info_struct *si)
#define TTRS_UNMAPPED 0x2
/* Reclaim the swap entry if swap is getting full */
#define TTRS_FULL 0x4
-/* Reclaim directly, bypass the slot cache and don't touch device lock */
-#define TTRS_DIRECT 0x8
static bool swap_only_has_cache(struct swap_info_struct *si,
unsigned long offset, int nr_pages)
@@ -257,23 +255,8 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
if (!need_reclaim)
goto out_unlock;
- if (!(flags & TTRS_DIRECT)) {
- /* Free through slot cache */
- delete_from_swap_cache(folio);
- folio_set_dirty(folio);
- ret = nr_pages;
- goto out_unlock;
- }
-
- xa_lock_irq(&address_space->i_pages);
- __delete_from_swap_cache(folio, entry, NULL);
- xa_unlock_irq(&address_space->i_pages);
- folio_ref_sub(folio, nr_pages);
+ delete_from_swap_cache(folio);
folio_set_dirty(folio);
-
- ci = lock_cluster(si, offset);
- swap_entry_range_free(si, ci, entry, nr_pages);
- unlock_cluster(ci);
ret = nr_pages;
out_unlock:
folio_unlock(folio);
@@ -697,7 +680,7 @@ static bool cluster_reclaim_range(struct swap_info_struct *si,
offset++;
break;
case SWAP_HAS_CACHE:
- nr_reclaim = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY | TTRS_DIRECT);
+ nr_reclaim = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY);
if (nr_reclaim > 0)
offset += nr_reclaim;
else
@@ -849,7 +832,7 @@ static void swap_reclaim_full_clusters(struct swap_info_struct *si, bool force)
if (READ_ONCE(map[offset]) == SWAP_HAS_CACHE) {
spin_unlock(&ci->lock);
nr_reclaim = __try_to_reclaim_swap(si, offset,
- TTRS_ANYWAY | TTRS_DIRECT);
+ TTRS_ANYWAY);
spin_lock(&ci->lock);
if (nr_reclaim) {
offset += abs(nr_reclaim);
--
2.48.1
^ permalink raw reply [flat|nested] 14+ messages in thread* [PATCH v2 3/7] mm, swap: avoid redundant swap device pinning
2025-02-24 18:02 [PATCH v2 0/7] mm, swap: remove swap slot cache Kairui Song
2025-02-24 18:02 ` [PATCH v2 1/7] mm, swap: avoid reclaiming irrelevant swap cache Kairui Song
2025-02-24 18:02 ` [PATCH v2 2/7] mm, swap: drop the flag TTRS_DIRECT Kairui Song
@ 2025-02-24 18:02 ` Kairui Song
2025-02-24 18:02 ` [PATCH v2 4/7] mm, swap: don't update the counter up-front Kairui Song
` (3 subsequent siblings)
6 siblings, 0 replies; 14+ messages in thread
From: Kairui Song @ 2025-02-24 18:02 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Chris Li, Barry Song, Hugh Dickins, Yosry Ahmed,
Huang, Ying, Baoquan He, Nhat Pham, Johannes Weiner, Baolin Wang,
Kalesh Singh, Matthew Wilcox, linux-kernel, Kairui Song
From: Kairui Song <kasong@tencent.com>
Currently __read_swap_cache_async() has get/put_swap_device() calls to
increase/decrease a swap device reference to prevent swapoff. While some
of its callers have already held the swap device reference, e.g in
do_swap_page() and shmem_swapin_folio() where __read_swap_cache_async()
will finally called. Now there are only two callers not holding a swap
device reference, so make them hold a reference instead. And drop the
get/put_swap_device calls in __read_swap_cache_async. This should reduce
the overhead for swap in during page fault slightly.
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
---
mm/swap_state.c | 14 ++++++++------
mm/zswap.c | 6 ++++++
2 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/mm/swap_state.c b/mm/swap_state.c
index a54b035d6a6c..50840a2887a5 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -426,17 +426,13 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
struct mempolicy *mpol, pgoff_t ilx, bool *new_page_allocated,
bool skip_if_exists)
{
- struct swap_info_struct *si;
+ struct swap_info_struct *si = swp_swap_info(entry);
struct folio *folio;
struct folio *new_folio = NULL;
struct folio *result = NULL;
void *shadow = NULL;
*new_page_allocated = false;
- si = get_swap_device(entry);
- if (!si)
- return NULL;
-
for (;;) {
int err;
/*
@@ -532,7 +528,6 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
put_swap_folio(new_folio, entry);
folio_unlock(new_folio);
put_and_return:
- put_swap_device(si);
if (!(*new_page_allocated) && new_folio)
folio_put(new_folio);
return result;
@@ -552,11 +547,16 @@ struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
struct vm_area_struct *vma, unsigned long addr,
struct swap_iocb **plug)
{
+ struct swap_info_struct *si;
bool page_allocated;
struct mempolicy *mpol;
pgoff_t ilx;
struct folio *folio;
+ si = get_swap_device(entry);
+ if (!si)
+ return NULL;
+
mpol = get_vma_policy(vma, addr, 0, &ilx);
folio = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
&page_allocated, false);
@@ -564,6 +564,8 @@ struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
if (page_allocated)
swap_read_folio(folio, plug);
+
+ put_swap_device(si);
return folio;
}
diff --git a/mm/zswap.c b/mm/zswap.c
index ac9d299e7d0c..83dfa1f9e689 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1051,14 +1051,20 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
struct folio *folio;
struct mempolicy *mpol;
bool folio_was_allocated;
+ struct swap_info_struct *si;
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
};
/* try to allocate swap cache folio */
+ si = get_swap_device(swpentry);
+ if (!si)
+ return -EEXIST;
+
mpol = get_task_policy(current);
folio = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
NO_INTERLEAVE_INDEX, &folio_was_allocated, true);
+ put_swap_device(si);
if (!folio)
return -ENOMEM;
--
2.48.1
^ permalink raw reply [flat|nested] 14+ messages in thread* [PATCH v2 4/7] mm, swap: don't update the counter up-front
2025-02-24 18:02 [PATCH v2 0/7] mm, swap: remove swap slot cache Kairui Song
` (2 preceding siblings ...)
2025-02-24 18:02 ` [PATCH v2 3/7] mm, swap: avoid redundant swap device pinning Kairui Song
@ 2025-02-24 18:02 ` Kairui Song
2025-02-25 6:32 ` Baoquan He
2025-02-24 18:02 ` [PATCH v2 5/7] mm, swap: use percpu cluster as allocation fast path Kairui Song
` (2 subsequent siblings)
6 siblings, 1 reply; 14+ messages in thread
From: Kairui Song @ 2025-02-24 18:02 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Chris Li, Barry Song, Hugh Dickins, Yosry Ahmed,
Huang, Ying, Baoquan He, Nhat Pham, Johannes Weiner, Baolin Wang,
Kalesh Singh, Matthew Wilcox, linux-kernel, Kairui Song
From: Kairui Song <kasong@tencent.com>
The counter update before allocation design was useful to avoid
unnecessary scan when device is full, so it will abort early if the
counter indicates the device is full. But that is an uncommon case,
and now scanning of a full device is very fast, so the up-front update
is not helpful any more.
Remove it and simplify the slot allocation logic.
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/swapfile.c | 18 ++----------------
1 file changed, 2 insertions(+), 16 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6f2de59c6355..db836670c334 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1201,22 +1201,10 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
int order = swap_entry_order(entry_order);
unsigned long size = 1 << order;
struct swap_info_struct *si, *next;
- long avail_pgs;
int n_ret = 0;
int node;
spin_lock(&swap_avail_lock);
-
- avail_pgs = atomic_long_read(&nr_swap_pages) / size;
- if (avail_pgs <= 0) {
- spin_unlock(&swap_avail_lock);
- goto noswap;
- }
-
- n_goal = min3((long)n_goal, (long)SWAP_BATCH, avail_pgs);
-
- atomic_long_sub(n_goal * size, &nr_swap_pages);
-
start_over:
node = numa_node_id();
plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
@@ -1250,10 +1238,8 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
spin_unlock(&swap_avail_lock);
check_out:
- if (n_ret < n_goal)
- atomic_long_add((long)(n_goal - n_ret) * size,
- &nr_swap_pages);
-noswap:
+ atomic_long_sub(n_ret * size, &nr_swap_pages);
+
return n_ret;
}
--
2.48.1
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH v2 4/7] mm, swap: don't update the counter up-front
2025-02-24 18:02 ` [PATCH v2 4/7] mm, swap: don't update the counter up-front Kairui Song
@ 2025-02-25 6:32 ` Baoquan He
0 siblings, 0 replies; 14+ messages in thread
From: Baoquan He @ 2025-02-25 6:32 UTC (permalink / raw)
To: Kairui Song
Cc: linux-mm, Andrew Morton, Chris Li, Barry Song, Hugh Dickins,
Yosry Ahmed, Huang, Ying, Nhat Pham, Johannes Weiner,
Baolin Wang, Kalesh Singh, Matthew Wilcox, linux-kernel
On 02/25/25 at 02:02am, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
>
> The counter update before allocation design was useful to avoid
> unnecessary scan when device is full, so it will abort early if the
> counter indicates the device is full. But that is an uncommon case,
> and now scanning of a full device is very fast, so the up-front update
> is not helpful any more.
>
> Remove it and simplify the slot allocation logic.
>
> Signed-off-by: Kairui Song <kasong@tencent.com>
> ---
> mm/swapfile.c | 18 ++----------------
> 1 file changed, 2 insertions(+), 16 deletions(-)
Reviewed-by: Baoquan He <bhe@redhat.com>
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 6f2de59c6355..db836670c334 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1201,22 +1201,10 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
> int order = swap_entry_order(entry_order);
> unsigned long size = 1 << order;
> struct swap_info_struct *si, *next;
> - long avail_pgs;
> int n_ret = 0;
> int node;
>
> spin_lock(&swap_avail_lock);
> -
> - avail_pgs = atomic_long_read(&nr_swap_pages) / size;
> - if (avail_pgs <= 0) {
> - spin_unlock(&swap_avail_lock);
> - goto noswap;
> - }
> -
> - n_goal = min3((long)n_goal, (long)SWAP_BATCH, avail_pgs);
> -
> - atomic_long_sub(n_goal * size, &nr_swap_pages);
> -
> start_over:
> node = numa_node_id();
> plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
> @@ -1250,10 +1238,8 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
> spin_unlock(&swap_avail_lock);
>
> check_out:
> - if (n_ret < n_goal)
> - atomic_long_add((long)(n_goal - n_ret) * size,
> - &nr_swap_pages);
> -noswap:
> + atomic_long_sub(n_ret * size, &nr_swap_pages);
> +
> return n_ret;
> }
>
> --
> 2.48.1
>
^ permalink raw reply [flat|nested] 14+ messages in thread
* [PATCH v2 5/7] mm, swap: use percpu cluster as allocation fast path
2025-02-24 18:02 [PATCH v2 0/7] mm, swap: remove swap slot cache Kairui Song
` (3 preceding siblings ...)
2025-02-24 18:02 ` [PATCH v2 4/7] mm, swap: don't update the counter up-front Kairui Song
@ 2025-02-24 18:02 ` Kairui Song
2025-02-25 4:01 ` Baoquan He
` (2 more replies)
2025-02-24 18:02 ` [PATCH v2 6/7] mm, swap: remove swap slot cache Kairui Song
2025-02-24 18:02 ` [PATCH v2 7/7] mm, swap: simplify folio swap allocation Kairui Song
6 siblings, 3 replies; 14+ messages in thread
From: Kairui Song @ 2025-02-24 18:02 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Chris Li, Barry Song, Hugh Dickins, Yosry Ahmed,
Huang, Ying, Baoquan He, Nhat Pham, Johannes Weiner, Baolin Wang,
Kalesh Singh, Matthew Wilcox, linux-kernel, Kairui Song
From: Kairui Song <kasong@tencent.com>
Current allocation workflow first traverses the plist with a global lock
held, after choosing a device, it uses the percpu cluster on that swap
device. This commit moves the percpu cluster variable out of being tied
to individual swap devices, making it a global percpu variable, and will
be used directly for allocation as a fast path.
The global percpu cluster variable will never point to a HDD device, and
allocations on a HDD device are still globally serialized.
This improves the allocator performance and prepares for removal of the
slot cache in later commits. There shouldn't be much observable behavior
change, except one thing: this changes how swap device allocation
rotation works.
Currently, each allocation will rotate the plist, and because of the
existence of slot cache (one order 0 allocation usually returns 64
entries), swap devices of the same priority are rotated for every 64
order 0 entries consumed. High order allocations are different, they
will bypass the slot cache, and so swap device is rotated for every
16K, 32K, or up to 2M allocation.
The rotation rule was never clearly defined or documented, it was changed
several times without mentioning.
After this commit, and once slot cache is gone in later commits, swap
device rotation will happen for every consumed cluster. Ideally non-HDD
devices will be rotated if 2M space has been consumed for each order.
Fragmented clusters will rotate the device faster, which seems OK.
HDD devices is rotated for every allocation regardless of the allocation
order, which should be OK too and trivial.
This commit also slightly changes allocation behaviour for slot cache.
The new added cluster allocation fast path may allocate entries from
different device to the slot cache, this is not observable from user
space, only impact performance very slightly, and slot cache will be
just gone in next commit, so this can be ignored.
Signed-off-by: Kairui Song <kasong@tencent.com>
---
include/linux/swap.h | 11 ++--
mm/swapfile.c | 136 +++++++++++++++++++++++++++++--------------
2 files changed, 95 insertions(+), 52 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 2fe91c293636..374bffc87427 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -284,12 +284,10 @@ enum swap_cluster_flags {
#endif
/*
- * We assign a cluster to each CPU, so each CPU can allocate swap entry from
- * its own cluster and swapout sequentially. The purpose is to optimize swapout
- * throughput.
+ * We keep using same cluster for rotational device so IO will be sequential.
+ * The purpose is to optimize SWAP throughput on these device.
*/
-struct percpu_cluster {
- local_lock_t lock; /* Protect the percpu_cluster above */
+struct swap_sequential_cluster {
unsigned int next[SWAP_NR_ORDERS]; /* Likely next allocation offset */
};
@@ -315,8 +313,7 @@ struct swap_info_struct {
atomic_long_t frag_cluster_nr[SWAP_NR_ORDERS];
unsigned int pages; /* total of usable pages of swap */
atomic_long_t inuse_pages; /* number of those currently in use */
- struct percpu_cluster __percpu *percpu_cluster; /* per cpu's swap location */
- struct percpu_cluster *global_cluster; /* Use one global cluster for rotating device */
+ struct swap_sequential_cluster *global_cluster; /* Use one global cluster for rotating device */
spinlock_t global_cluster_lock; /* Serialize usage of global cluster */
struct rb_root swap_extent_root;/* root of the swap extent rbtree */
struct block_device *bdev; /* swap device or bdev of swap file */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index db836670c334..7caaaea95408 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -116,6 +116,18 @@ static atomic_t proc_poll_event = ATOMIC_INIT(0);
atomic_t nr_rotate_swap = ATOMIC_INIT(0);
+struct percpu_swap_cluster {
+ struct swap_info_struct *si[SWAP_NR_ORDERS];
+ unsigned long offset[SWAP_NR_ORDERS];
+ local_lock_t lock;
+};
+
+static DEFINE_PER_CPU(struct percpu_swap_cluster, percpu_swap_cluster) = {
+ .si = { NULL },
+ .offset = { SWAP_ENTRY_INVALID },
+ .lock = INIT_LOCAL_LOCK(),
+};
+
static struct swap_info_struct *swap_type_to_swap_info(int type)
{
if (type >= MAX_SWAPFILES)
@@ -539,7 +551,7 @@ static bool swap_do_scheduled_discard(struct swap_info_struct *si)
ci = list_first_entry(&si->discard_clusters, struct swap_cluster_info, list);
/*
* Delete the cluster from list to prepare for discard, but keep
- * the CLUSTER_FLAG_DISCARD flag, there could be percpu_cluster
+ * the CLUSTER_FLAG_DISCARD flag, percpu_swap_cluster could be
* pointing to it, or ran into by relocate_cluster.
*/
list_del(&ci->list);
@@ -805,10 +817,12 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si,
out:
relocate_cluster(si, ci);
unlock_cluster(ci);
- if (si->flags & SWP_SOLIDSTATE)
- __this_cpu_write(si->percpu_cluster->next[order], next);
- else
+ if (si->flags & SWP_SOLIDSTATE) {
+ __this_cpu_write(percpu_swap_cluster.si[order], si);
+ __this_cpu_write(percpu_swap_cluster.offset[order], next);
+ } else {
si->global_cluster->next[order] = next;
+ }
return found;
}
@@ -862,9 +876,8 @@ static void swap_reclaim_work(struct work_struct *work)
}
/*
- * Try to get swap entries with specified order from current cpu's swap entry
- * pool (a cluster). This might involve allocating a new cluster for current CPU
- * too.
+ * Try to allocate swap entries with specified order and try set a new
+ * cluster for current CPU too.
*/
static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int order,
unsigned char usage)
@@ -872,18 +885,12 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
struct swap_cluster_info *ci;
unsigned int offset, found = 0;
- if (si->flags & SWP_SOLIDSTATE) {
- /* Fast path using per CPU cluster */
- local_lock(&si->percpu_cluster->lock);
- offset = __this_cpu_read(si->percpu_cluster->next[order]);
- } else {
+ if (!(si->flags & SWP_SOLIDSTATE)) {
/* Serialize HDD SWAP allocation for each device. */
spin_lock(&si->global_cluster_lock);
offset = si->global_cluster->next[order];
- }
-
- if (offset) {
ci = lock_cluster(si, offset);
+
/* Cluster could have been used by another order */
if (cluster_is_usable(ci, order)) {
if (cluster_is_empty(ci))
@@ -973,9 +980,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
}
}
done:
- if (si->flags & SWP_SOLIDSTATE)
- local_unlock(&si->percpu_cluster->lock);
- else
+ if (!(si->flags & SWP_SOLIDSTATE))
spin_unlock(&si->global_cluster_lock);
return found;
}
@@ -1196,6 +1201,49 @@ static bool get_swap_device_info(struct swap_info_struct *si)
return true;
}
+/*
+ * Fast path try to get swap entries with specified order from current
+ * CPU's swap entry pool (a cluster).
+ */
+static int swap_alloc_fast(swp_entry_t entries[],
+ unsigned char usage,
+ int order, int n_goal)
+{
+ struct swap_cluster_info *ci;
+ struct swap_info_struct *si;
+ unsigned int offset, found;
+ int n_ret = 0;
+
+ n_goal = min(n_goal, SWAP_BATCH);
+
+ /*
+ * Once allocated, swap_info_struct will never be completely freed,
+ * so checking it's liveness by get_swap_device_info is enough.
+ */
+ si = __this_cpu_read(percpu_swap_cluster.si[order]);
+ offset = __this_cpu_read(percpu_swap_cluster.offset[order]);
+ if (!si || !offset || !get_swap_device_info(si))
+ return 0;
+
+ while (offset) {
+ ci = lock_cluster(si, offset);
+ if (!cluster_is_usable(ci, order))
+ break;
+ if (cluster_is_empty(ci))
+ offset = cluster_offset(si, ci);
+ found = alloc_swap_scan_cluster(si, ci, offset, order, usage);
+ if (!found)
+ break;
+ entries[n_ret++] = swp_entry(si->type, found);
+ if (n_ret == n_goal)
+ break;
+ offset = __this_cpu_read(percpu_swap_cluster.offset[order]);
+ }
+
+ put_swap_device(si);
+ return n_ret;
+}
+
int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
{
int order = swap_entry_order(entry_order);
@@ -1204,19 +1252,36 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
int n_ret = 0;
int node;
+ /* Fast path using percpu cluster */
+ local_lock(&percpu_swap_cluster.lock);
+ n_ret = swap_alloc_fast(swp_entries,
+ SWAP_HAS_CACHE,
+ order, n_goal);
+ if (n_ret == n_goal)
+ goto out;
+
+ n_goal = min_t(int, n_goal - n_ret, SWAP_BATCH);
+ /* Rotate the device and switch to a new cluster */
spin_lock(&swap_avail_lock);
start_over:
node = numa_node_id();
plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
- /* requeue si to after same-priority siblings */
plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
spin_unlock(&swap_avail_lock);
if (get_swap_device_info(si)) {
- n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
- n_goal, swp_entries, order);
+ /*
+ * For order 0 allocation, try best to fill the request
+ * as it's used by slot cache.
+ *
+ * For mTHP allocation, it always have n_goal == 1,
+ * and falling a mTHP swapin will just make the caller
+ * fallback to order 0 allocation, so just bail out.
+ */
+ n_ret += scan_swap_map_slots(si, SWAP_HAS_CACHE, n_goal,
+ swp_entries + n_ret, order);
put_swap_device(si);
if (n_ret || size > 1)
- goto check_out;
+ goto out;
}
spin_lock(&swap_avail_lock);
@@ -1234,12 +1299,10 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
if (plist_node_empty(&next->avail_lists[node]))
goto start_over;
}
-
spin_unlock(&swap_avail_lock);
-
-check_out:
+out:
+ local_unlock(&percpu_swap_cluster.lock);
atomic_long_sub(n_ret * size, &nr_swap_pages);
-
return n_ret;
}
@@ -2725,8 +2788,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
arch_swap_invalidate_area(p->type);
zswap_swapoff(p->type);
mutex_unlock(&swapon_mutex);
- free_percpu(p->percpu_cluster);
- p->percpu_cluster = NULL;
kfree(p->global_cluster);
p->global_cluster = NULL;
vfree(swap_map);
@@ -3125,7 +3186,7 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
struct swap_cluster_info *cluster_info;
unsigned long i, j, idx;
- int cpu, err = -ENOMEM;
+ int err = -ENOMEM;
cluster_info = kvcalloc(nr_clusters, sizeof(*cluster_info), GFP_KERNEL);
if (!cluster_info)
@@ -3134,20 +3195,7 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
for (i = 0; i < nr_clusters; i++)
spin_lock_init(&cluster_info[i].lock);
- if (si->flags & SWP_SOLIDSTATE) {
- si->percpu_cluster = alloc_percpu(struct percpu_cluster);
- if (!si->percpu_cluster)
- goto err_free;
-
- for_each_possible_cpu(cpu) {
- struct percpu_cluster *cluster;
-
- cluster = per_cpu_ptr(si->percpu_cluster, cpu);
- for (i = 0; i < SWAP_NR_ORDERS; i++)
- cluster->next[i] = SWAP_ENTRY_INVALID;
- local_lock_init(&cluster->lock);
- }
- } else {
+ if (!(si->flags & SWP_SOLIDSTATE)) {
si->global_cluster = kmalloc(sizeof(*si->global_cluster),
GFP_KERNEL);
if (!si->global_cluster)
@@ -3424,8 +3472,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
bad_swap_unlock_inode:
inode_unlock(inode);
bad_swap:
- free_percpu(si->percpu_cluster);
- si->percpu_cluster = NULL;
kfree(si->global_cluster);
si->global_cluster = NULL;
inode = NULL;
--
2.48.1
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH v2 5/7] mm, swap: use percpu cluster as allocation fast path
2025-02-24 18:02 ` [PATCH v2 5/7] mm, swap: use percpu cluster as allocation fast path Kairui Song
@ 2025-02-25 4:01 ` Baoquan He
2025-02-25 6:38 ` Baoquan He
2025-03-07 2:54 ` Kairui Song
2 siblings, 0 replies; 14+ messages in thread
From: Baoquan He @ 2025-02-25 4:01 UTC (permalink / raw)
To: Kairui Song
Cc: linux-mm, Andrew Morton, Chris Li, Barry Song, Hugh Dickins,
Yosry Ahmed, Huang, Ying, Nhat Pham, Johannes Weiner,
Baolin Wang, Kalesh Singh, Matthew Wilcox, linux-kernel
On 02/25/25 at 02:02am, Kairui Song wrote:
......snip...
> @@ -1204,19 +1252,36 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
> int n_ret = 0;
> int node;
>
> + /* Fast path using percpu cluster */
> + local_lock(&percpu_swap_cluster.lock);
> + n_ret = swap_alloc_fast(swp_entries,
> + SWAP_HAS_CACHE,
> + order, n_goal);
Since we always pass in the SWAP_HAS_CACHE for the 2nd parameter, we can
hard code it inside fucntion swap_alloc_fast(), unless there will be
other callsite where different value is passed in for 'usage'. And the
function 2nd parameter of swap_alloc_slow() too. Anyway, it's not a big
deal, could be my personal peference.
Other than this nit, this looks good to me.
> + if (n_ret == n_goal)
> + goto out;
> +
> + n_goal = min_t(int, n_goal - n_ret, SWAP_BATCH);
> + /* Rotate the device and switch to a new cluster */
> spin_lock(&swap_avail_lock);
> start_over:
> node = numa_node_id();
> plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
> - /* requeue si to after same-priority siblings */
> plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
> spin_unlock(&swap_avail_lock);
> if (get_swap_device_info(si)) {
> - n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
> - n_goal, swp_entries, order);
> + /*
> + * For order 0 allocation, try best to fill the request
> + * as it's used by slot cache.
> + *
> + * For mTHP allocation, it always have n_goal == 1,
> + * and falling a mTHP swapin will just make the caller
> + * fallback to order 0 allocation, so just bail out.
> + */
> + n_ret += scan_swap_map_slots(si, SWAP_HAS_CACHE, n_goal,
> + swp_entries + n_ret, order);
> put_swap_device(si);
> if (n_ret || size > 1)
> - goto check_out;
> + goto out;
> }
>
> spin_lock(&swap_avail_lock);
> @@ -1234,12 +1299,10 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
> if (plist_node_empty(&next->avail_lists[node]))
> goto start_over;
> }
> -
> spin_unlock(&swap_avail_lock);
> -
> -check_out:
> +out:
> + local_unlock(&percpu_swap_cluster.lock);
> atomic_long_sub(n_ret * size, &nr_swap_pages);
> -
> return n_ret;
> }
>
> @@ -2725,8 +2788,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
> arch_swap_invalidate_area(p->type);
> zswap_swapoff(p->type);
> mutex_unlock(&swapon_mutex);
> - free_percpu(p->percpu_cluster);
> - p->percpu_cluster = NULL;
> kfree(p->global_cluster);
> p->global_cluster = NULL;
> vfree(swap_map);
> @@ -3125,7 +3186,7 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
> unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
> struct swap_cluster_info *cluster_info;
> unsigned long i, j, idx;
> - int cpu, err = -ENOMEM;
> + int err = -ENOMEM;
>
> cluster_info = kvcalloc(nr_clusters, sizeof(*cluster_info), GFP_KERNEL);
> if (!cluster_info)
> @@ -3134,20 +3195,7 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
> for (i = 0; i < nr_clusters; i++)
> spin_lock_init(&cluster_info[i].lock);
>
> - if (si->flags & SWP_SOLIDSTATE) {
> - si->percpu_cluster = alloc_percpu(struct percpu_cluster);
> - if (!si->percpu_cluster)
> - goto err_free;
> -
> - for_each_possible_cpu(cpu) {
> - struct percpu_cluster *cluster;
> -
> - cluster = per_cpu_ptr(si->percpu_cluster, cpu);
> - for (i = 0; i < SWAP_NR_ORDERS; i++)
> - cluster->next[i] = SWAP_ENTRY_INVALID;
> - local_lock_init(&cluster->lock);
> - }
> - } else {
> + if (!(si->flags & SWP_SOLIDSTATE)) {
> si->global_cluster = kmalloc(sizeof(*si->global_cluster),
> GFP_KERNEL);
> if (!si->global_cluster)
> @@ -3424,8 +3472,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> bad_swap_unlock_inode:
> inode_unlock(inode);
> bad_swap:
> - free_percpu(si->percpu_cluster);
> - si->percpu_cluster = NULL;
> kfree(si->global_cluster);
> si->global_cluster = NULL;
> inode = NULL;
> --
> 2.48.1
>
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH v2 5/7] mm, swap: use percpu cluster as allocation fast path
2025-02-24 18:02 ` [PATCH v2 5/7] mm, swap: use percpu cluster as allocation fast path Kairui Song
2025-02-25 4:01 ` Baoquan He
@ 2025-02-25 6:38 ` Baoquan He
2025-03-07 2:54 ` Kairui Song
2 siblings, 0 replies; 14+ messages in thread
From: Baoquan He @ 2025-02-25 6:38 UTC (permalink / raw)
To: Kairui Song
Cc: linux-mm, Andrew Morton, Chris Li, Barry Song, Hugh Dickins,
Yosry Ahmed, Huang, Ying, Nhat Pham, Johannes Weiner,
Baolin Wang, Kalesh Singh, Matthew Wilcox, linux-kernel
On 02/25/25 at 02:02am, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
>
> Current allocation workflow first traverses the plist with a global lock
> held, after choosing a device, it uses the percpu cluster on that swap
> device. This commit moves the percpu cluster variable out of being tied
> to individual swap devices, making it a global percpu variable, and will
> be used directly for allocation as a fast path.
>
> The global percpu cluster variable will never point to a HDD device, and
> allocations on a HDD device are still globally serialized.
>
> This improves the allocator performance and prepares for removal of the
> slot cache in later commits. There shouldn't be much observable behavior
> change, except one thing: this changes how swap device allocation
> rotation works.
>
> Currently, each allocation will rotate the plist, and because of the
> existence of slot cache (one order 0 allocation usually returns 64
> entries), swap devices of the same priority are rotated for every 64
> order 0 entries consumed. High order allocations are different, they
> will bypass the slot cache, and so swap device is rotated for every
> 16K, 32K, or up to 2M allocation.
>
> The rotation rule was never clearly defined or documented, it was changed
> several times without mentioning.
>
> After this commit, and once slot cache is gone in later commits, swap
> device rotation will happen for every consumed cluster. Ideally non-HDD
> devices will be rotated if 2M space has been consumed for each order.
> Fragmented clusters will rotate the device faster, which seems OK.
> HDD devices is rotated for every allocation regardless of the allocation
> order, which should be OK too and trivial.
>
> This commit also slightly changes allocation behaviour for slot cache.
> The new added cluster allocation fast path may allocate entries from
> different device to the slot cache, this is not observable from user
> space, only impact performance very slightly, and slot cache will be
> just gone in next commit, so this can be ignored.
>
> Signed-off-by: Kairui Song <kasong@tencent.com>
> ---
> include/linux/swap.h | 11 ++--
> mm/swapfile.c | 136 +++++++++++++++++++++++++++++--------------
> 2 files changed, 95 insertions(+), 52 deletions(-)
Reviewed-by: Baoquan He <bhe@redhat.com>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v2 5/7] mm, swap: use percpu cluster as allocation fast path
2025-02-24 18:02 ` [PATCH v2 5/7] mm, swap: use percpu cluster as allocation fast path Kairui Song
2025-02-25 4:01 ` Baoquan He
2025-02-25 6:38 ` Baoquan He
@ 2025-03-07 2:54 ` Kairui Song
2 siblings, 0 replies; 14+ messages in thread
From: Kairui Song @ 2025-03-07 2:54 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Chris Li, Barry Song, Hugh Dickins, Yosry Ahmed,
Huang, Ying, Baoquan He, Nhat Pham, Johannes Weiner, Baolin Wang,
Kalesh Singh, Matthew Wilcox, linux-kernel, Kairui Song
On Tue, Feb 25, 2025 at 2:03 AM Kairui Song <ryncsn@gmail.com> wrote:
>
> From: Kairui Song <kasong@tencent.com>
>
> Current allocation workflow first traverses the plist with a global lock
> held, after choosing a device, it uses the percpu cluster on that swap
> device. This commit moves the percpu cluster variable out of being tied
> to individual swap devices, making it a global percpu variable, and will
> be used directly for allocation as a fast path.
>
> The global percpu cluster variable will never point to a HDD device, and
> allocations on a HDD device are still globally serialized.
>
> This improves the allocator performance and prepares for removal of the
> slot cache in later commits. There shouldn't be much observable behavior
> change, except one thing: this changes how swap device allocation
> rotation works.
>
> Currently, each allocation will rotate the plist, and because of the
> existence of slot cache (one order 0 allocation usually returns 64
> entries), swap devices of the same priority are rotated for every 64
> order 0 entries consumed. High order allocations are different, they
> will bypass the slot cache, and so swap device is rotated for every
> 16K, 32K, or up to 2M allocation.
>
> The rotation rule was never clearly defined or documented, it was changed
> several times without mentioning.
>
> After this commit, and once slot cache is gone in later commits, swap
> device rotation will happen for every consumed cluster. Ideally non-HDD
> devices will be rotated if 2M space has been consumed for each order.
> Fragmented clusters will rotate the device faster, which seems OK.
> HDD devices is rotated for every allocation regardless of the allocation
> order, which should be OK too and trivial.
>
> This commit also slightly changes allocation behaviour for slot cache.
> The new added cluster allocation fast path may allocate entries from
> different device to the slot cache, this is not observable from user
> space, only impact performance very slightly, and slot cache will be
> just gone in next commit, so this can be ignored.
>
> Signed-off-by: Kairui Song <kasong@tencent.com>
> ---
> include/linux/swap.h | 11 ++--
> mm/swapfile.c | 136 +++++++++++++++++++++++++++++--------------
> 2 files changed, 95 insertions(+), 52 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 2fe91c293636..374bffc87427 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -284,12 +284,10 @@ enum swap_cluster_flags {
> #endif
>
> /*
> - * We assign a cluster to each CPU, so each CPU can allocate swap entry from
> - * its own cluster and swapout sequentially. The purpose is to optimize swapout
> - * throughput.
> + * We keep using same cluster for rotational device so IO will be sequential.
> + * The purpose is to optimize SWAP throughput on these device.
> */
> -struct percpu_cluster {
> - local_lock_t lock; /* Protect the percpu_cluster above */
> +struct swap_sequential_cluster {
> unsigned int next[SWAP_NR_ORDERS]; /* Likely next allocation offset */
> };
>
> @@ -315,8 +313,7 @@ struct swap_info_struct {
> atomic_long_t frag_cluster_nr[SWAP_NR_ORDERS];
> unsigned int pages; /* total of usable pages of swap */
> atomic_long_t inuse_pages; /* number of those currently in use */
> - struct percpu_cluster __percpu *percpu_cluster; /* per cpu's swap location */
> - struct percpu_cluster *global_cluster; /* Use one global cluster for rotating device */
> + struct swap_sequential_cluster *global_cluster; /* Use one global cluster for rotating device */
> spinlock_t global_cluster_lock; /* Serialize usage of global cluster */
> struct rb_root swap_extent_root;/* root of the swap extent rbtree */
> struct block_device *bdev; /* swap device or bdev of swap file */
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index db836670c334..7caaaea95408 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -116,6 +116,18 @@ static atomic_t proc_poll_event = ATOMIC_INIT(0);
>
> atomic_t nr_rotate_swap = ATOMIC_INIT(0);
>
> +struct percpu_swap_cluster {
> + struct swap_info_struct *si[SWAP_NR_ORDERS];
> + unsigned long offset[SWAP_NR_ORDERS];
> + local_lock_t lock;
> +};
> +
> +static DEFINE_PER_CPU(struct percpu_swap_cluster, percpu_swap_cluster) = {
> + .si = { NULL },
> + .offset = { SWAP_ENTRY_INVALID },
> + .lock = INIT_LOCAL_LOCK(),
> +};
> +
> static struct swap_info_struct *swap_type_to_swap_info(int type)
> {
> if (type >= MAX_SWAPFILES)
> @@ -539,7 +551,7 @@ static bool swap_do_scheduled_discard(struct swap_info_struct *si)
> ci = list_first_entry(&si->discard_clusters, struct swap_cluster_info, list);
> /*
> * Delete the cluster from list to prepare for discard, but keep
> - * the CLUSTER_FLAG_DISCARD flag, there could be percpu_cluster
> + * the CLUSTER_FLAG_DISCARD flag, percpu_swap_cluster could be
> * pointing to it, or ran into by relocate_cluster.
> */
> list_del(&ci->list);
> @@ -805,10 +817,12 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si,
> out:
> relocate_cluster(si, ci);
> unlock_cluster(ci);
> - if (si->flags & SWP_SOLIDSTATE)
> - __this_cpu_write(si->percpu_cluster->next[order], next);
> - else
> + if (si->flags & SWP_SOLIDSTATE) {
> + __this_cpu_write(percpu_swap_cluster.si[order], si);
> + __this_cpu_write(percpu_swap_cluster.offset[order], next);
> + } else {
> si->global_cluster->next[order] = next;
> + }
> return found;
> }
>
> @@ -862,9 +876,8 @@ static void swap_reclaim_work(struct work_struct *work)
> }
>
> /*
> - * Try to get swap entries with specified order from current cpu's swap entry
> - * pool (a cluster). This might involve allocating a new cluster for current CPU
> - * too.
> + * Try to allocate swap entries with specified order and try set a new
> + * cluster for current CPU too.
> */
> static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int order,
> unsigned char usage)
> @@ -872,18 +885,12 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
> struct swap_cluster_info *ci;
> unsigned int offset, found = 0;
>
> - if (si->flags & SWP_SOLIDSTATE) {
> - /* Fast path using per CPU cluster */
> - local_lock(&si->percpu_cluster->lock);
> - offset = __this_cpu_read(si->percpu_cluster->next[order]);
> - } else {
> + if (!(si->flags & SWP_SOLIDSTATE)) {
> /* Serialize HDD SWAP allocation for each device. */
> spin_lock(&si->global_cluster_lock);
> offset = si->global_cluster->next[order];
> - }
> -
> - if (offset) {
> ci = lock_cluster(si, offset);
> +
> /* Cluster could have been used by another order */
> if (cluster_is_usable(ci, order)) {
> if (cluster_is_empty(ci))
> @@ -973,9 +980,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
> }
> }
> done:
> - if (si->flags & SWP_SOLIDSTATE)
> - local_unlock(&si->percpu_cluster->lock);
> - else
> + if (!(si->flags & SWP_SOLIDSTATE))
> spin_unlock(&si->global_cluster_lock);
> return found;
> }
> @@ -1196,6 +1201,49 @@ static bool get_swap_device_info(struct swap_info_struct *si)
> return true;
> }
>
> +/*
> + * Fast path try to get swap entries with specified order from current
> + * CPU's swap entry pool (a cluster).
> + */
> +static int swap_alloc_fast(swp_entry_t entries[],
> + unsigned char usage,
> + int order, int n_goal)
> +{
> + struct swap_cluster_info *ci;
> + struct swap_info_struct *si;
> + unsigned int offset, found;
> + int n_ret = 0;
> +
> + n_goal = min(n_goal, SWAP_BATCH);
> +
> + /*
> + * Once allocated, swap_info_struct will never be completely freed,
> + * so checking it's liveness by get_swap_device_info is enough.
> + */
> + si = __this_cpu_read(percpu_swap_cluster.si[order]);
> + offset = __this_cpu_read(percpu_swap_cluster.offset[order]);
> + if (!si || !offset || !get_swap_device_info(si))
> + return 0;
Found one issue with this intermediate patch, "si" will be reused upon
swapoff & swapon again. So after the reuse, get_swap_device_info()
returns true and `offset` is not 0, but `offset` is invalid, it could
point to a value larger than si->max if the previous device is larger.
To fix it, need to squash this onto it:
(also include a code fix for cluster_is_usable check, this code error
is fixed by 7/7 but shouldn't be here in the first place)
(replacing __this_cpu_xx with this_cpu_xx because the swapoff flush
will access other CPU's variable now)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 7caaaea95408..68b40e74be93 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -818,8 +818,8 @@ static unsigned int alloc_swap_scan_cluster(struct
swap_info_struct *si,
relocate_cluster(si, ci);
unlock_cluster(ci);
if (si->flags & SWP_SOLIDSTATE) {
- __this_cpu_write(percpu_swap_cluster.si[order], si);
- __this_cpu_write(percpu_swap_cluster.offset[order], next);
+ this_cpu_write(percpu_swap_cluster.si[order], si);
+ this_cpu_write(percpu_swap_cluster.offset[order], next);
} else {
si->global_cluster->next[order] = next;
}
@@ -1220,15 +1220,17 @@ static int swap_alloc_fast(swp_entry_t entries[],
* Once allocated, swap_info_struct will never be completely freed,
* so checking it's liveness by get_swap_device_info is enough.
*/
- si = __this_cpu_read(percpu_swap_cluster.si[order]);
- offset = __this_cpu_read(percpu_swap_cluster.offset[order]);
+ si = this_cpu_read(percpu_swap_cluster.si[order]);
+ offset = this_cpu_read(percpu_swap_cluster.offset[order]);
if (!si || !offset || !get_swap_device_info(si))
return 0;
while (offset) {
ci = lock_cluster(si, offset);
- if (!cluster_is_usable(ci, order))
+ if (!cluster_is_usable(ci, order)) {
+ unlock_cluster(ci);
break;
+ }
if (cluster_is_empty(ci))
offset = cluster_offset(si, ci);
found = alloc_swap_scan_cluster(si, ci, offset, order, usage);
@@ -1237,7 +1239,7 @@ static int swap_alloc_fast(swp_entry_t entries[],
entries[n_ret++] = swp_entry(si->type, found);
if (n_ret == n_goal)
break;
- offset = __this_cpu_read(percpu_swap_cluster.offset[order]);
+ offset = this_cpu_read(percpu_swap_cluster.offset[order]);
}
put_swap_device(si);
@@ -2660,6 +2662,27 @@ static void wait_for_allocation(struct
swap_info_struct *si)
}
}
+/*
+ * Called after swap devices reference count is dead, so
+ * neither scan or allocation will go into it.
+ */
+static void flush_percpu_swap_cluster(struct swap_info_struct *si)
+{
+ int cpu;
+ struct swap_info_struct **pcp_si;
+
+ for_each_possible_cpu(cpu) {
+ pcp_si = per_cpu_ptr(percpu_swap_cluster.si, cpu);
+ /*
+ * Invalidate the percpu swap cluster, si->users
+ * is dead, so no new users will point to it, flush any
+ * existing cache is enough.
+ */
+ cmpxchg(pcp_si, si, NULL);
+ }
+}
+
+
SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
{
struct swap_info_struct *p = NULL;
@@ -2761,6 +2784,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
flush_work(&p->discard_work);
flush_work(&p->reclaim_work);
+ flush_percpu_swap_cluster(p);
destroy_swap_extents(p);
if (p->flags & SWP_CONTINUED)
---
There will be minor conflict in the next commit after this squash, I
will send a V3 shortly to resolve this if there is no objection on
this.
^ permalink raw reply [flat|nested] 14+ messages in thread
* [PATCH v2 6/7] mm, swap: remove swap slot cache
2025-02-24 18:02 [PATCH v2 0/7] mm, swap: remove swap slot cache Kairui Song
` (4 preceding siblings ...)
2025-02-24 18:02 ` [PATCH v2 5/7] mm, swap: use percpu cluster as allocation fast path Kairui Song
@ 2025-02-24 18:02 ` Kairui Song
2025-02-25 6:39 ` Baoquan He
2025-02-24 18:02 ` [PATCH v2 7/7] mm, swap: simplify folio swap allocation Kairui Song
6 siblings, 1 reply; 14+ messages in thread
From: Kairui Song @ 2025-02-24 18:02 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Chris Li, Barry Song, Hugh Dickins, Yosry Ahmed,
Huang, Ying, Baoquan He, Nhat Pham, Johannes Weiner, Baolin Wang,
Kalesh Singh, Matthew Wilcox, linux-kernel, Kairui Song
From: Kairui Song <kasong@tencent.com>
Slot cache is no longer needed now, removing it and all related code.
- vm-scalability with: `usemem --init-time -O -y -x -R -31 1G`,
12G memory cgroup using simulated pmem as SWAP (32G pmem, 32 CPUs),
16 test runs for each case, measuring the total throughput:
Before (KB/s) (stdev) After (KB/s) (stdev)
Random (4K): 424907.60 (24410.78) 414745.92 (34554.78)
Random (64K): 163308.82 (11635.72) 167314.50 (18434.99)
Sequential (4K, !-R): 6150056.79 (103205.90) 6321469.06 (115878.16)
The performance changes are below noise level.
- Build linux kernel with make -j96, using 4K folio with 1.5G memory
cgroup limit and 64K folio with 2G memory cgroup limit, on top of tmpfs,
12 test runs, measuring the system time:
Before (s) (stdev) After (s) (stdev)
make -j96 (4K): 6445.69 (61.95) 6408.80 (69.46)
make -j96 (64K): 6841.71 (409.04) 6437.99 (435.55)
Similar to above, 64k mTHP case showed a slight improvement.
Signed-off-by: Kairui Song <kasong@tencent.com>
---
include/linux/swap.h | 2 -
include/linux/swap_slots.h | 28 ----
mm/Makefile | 2 +-
mm/swap_slots.c | 295 -------------------------------------
mm/swap_state.c | 8 +-
mm/swapfile.c | 193 +++++++++---------------
6 files changed, 71 insertions(+), 457 deletions(-)
delete mode 100644 include/linux/swap_slots.h
delete mode 100644 mm/swap_slots.c
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 374bffc87427..a0a262bcaf41 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -465,7 +465,6 @@ void free_pages_and_swap_cache(struct encoded_page **, int);
extern atomic_long_t nr_swap_pages;
extern long total_swap_pages;
extern atomic_t nr_rotate_swap;
-extern bool has_usable_swap(void);
/* Swap 50% full? Release swapcache more aggressively.. */
static inline bool vm_swap_full(void)
@@ -489,7 +488,6 @@ extern void swap_shmem_alloc(swp_entry_t, int);
extern int swap_duplicate(swp_entry_t);
extern int swapcache_prepare(swp_entry_t entry, int nr);
extern void swap_free_nr(swp_entry_t entry, int nr_pages);
-extern void swapcache_free_entries(swp_entry_t *entries, int n);
extern void free_swap_and_cache_nr(swp_entry_t entry, int nr);
int swap_type_of(dev_t device, sector_t offset);
int find_first_swap(dev_t *device);
diff --git a/include/linux/swap_slots.h b/include/linux/swap_slots.h
deleted file mode 100644
index 840aec3523b2..000000000000
--- a/include/linux/swap_slots.h
+++ /dev/null
@@ -1,28 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _LINUX_SWAP_SLOTS_H
-#define _LINUX_SWAP_SLOTS_H
-
-#include <linux/swap.h>
-#include <linux/spinlock.h>
-#include <linux/mutex.h>
-
-#define SWAP_SLOTS_CACHE_SIZE SWAP_BATCH
-#define THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE (5*SWAP_SLOTS_CACHE_SIZE)
-#define THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE (2*SWAP_SLOTS_CACHE_SIZE)
-
-struct swap_slots_cache {
- bool lock_initialized;
- struct mutex alloc_lock; /* protects slots, nr, cur */
- swp_entry_t *slots;
- int nr;
- int cur;
- int n_ret;
-};
-
-void disable_swap_slots_cache_lock(void);
-void reenable_swap_slots_cache_unlock(void);
-void enable_swap_slots_cache(void);
-
-extern bool swap_slot_cache_enabled;
-
-#endif /* _LINUX_SWAP_SLOTS_H */
diff --git a/mm/Makefile b/mm/Makefile
index 4510a9869e77..e7f6bbf8ae5f 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -75,7 +75,7 @@ ifdef CONFIG_MMU
obj-$(CONFIG_ADVISE_SYSCALLS) += madvise.o
endif
-obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o swap_slots.o
+obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
obj-$(CONFIG_ZSWAP) += zswap.o
obj-$(CONFIG_HAS_DMA) += dmapool.o
obj-$(CONFIG_HUGETLBFS) += hugetlb.o
diff --git a/mm/swap_slots.c b/mm/swap_slots.c
deleted file mode 100644
index 9c7c171df7ba..000000000000
--- a/mm/swap_slots.c
+++ /dev/null
@@ -1,295 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * Manage cache of swap slots to be used for and returned from
- * swap.
- *
- * Copyright(c) 2016 Intel Corporation.
- *
- * Author: Tim Chen <tim.c.chen@linux.intel.com>
- *
- * We allocate the swap slots from the global pool and put
- * it into local per cpu caches. This has the advantage
- * of no needing to acquire the swap_info lock every time
- * we need a new slot.
- *
- * There is also opportunity to simply return the slot
- * to local caches without needing to acquire swap_info
- * lock. We do not reuse the returned slots directly but
- * move them back to the global pool in a batch. This
- * allows the slots to coalesce and reduce fragmentation.
- *
- * The swap entry allocated is marked with SWAP_HAS_CACHE
- * flag in map_count that prevents it from being allocated
- * again from the global pool.
- *
- * The swap slots cache is protected by a mutex instead of
- * a spin lock as when we search for slots with scan_swap_map,
- * we can possibly sleep.
- */
-
-#include <linux/swap_slots.h>
-#include <linux/cpu.h>
-#include <linux/cpumask.h>
-#include <linux/slab.h>
-#include <linux/vmalloc.h>
-#include <linux/mutex.h>
-#include <linux/mm.h>
-
-static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
-static bool swap_slot_cache_active;
-bool swap_slot_cache_enabled;
-static bool swap_slot_cache_initialized;
-static DEFINE_MUTEX(swap_slots_cache_mutex);
-/* Serialize swap slots cache enable/disable operations */
-static DEFINE_MUTEX(swap_slots_cache_enable_mutex);
-
-static void __drain_swap_slots_cache(void);
-
-#define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_enabled)
-
-static void deactivate_swap_slots_cache(void)
-{
- mutex_lock(&swap_slots_cache_mutex);
- swap_slot_cache_active = false;
- __drain_swap_slots_cache();
- mutex_unlock(&swap_slots_cache_mutex);
-}
-
-static void reactivate_swap_slots_cache(void)
-{
- mutex_lock(&swap_slots_cache_mutex);
- swap_slot_cache_active = true;
- mutex_unlock(&swap_slots_cache_mutex);
-}
-
-/* Must not be called with cpu hot plug lock */
-void disable_swap_slots_cache_lock(void)
-{
- mutex_lock(&swap_slots_cache_enable_mutex);
- swap_slot_cache_enabled = false;
- if (swap_slot_cache_initialized) {
- /* serialize with cpu hotplug operations */
- cpus_read_lock();
- __drain_swap_slots_cache();
- cpus_read_unlock();
- }
-}
-
-static void __reenable_swap_slots_cache(void)
-{
- swap_slot_cache_enabled = has_usable_swap();
-}
-
-void reenable_swap_slots_cache_unlock(void)
-{
- __reenable_swap_slots_cache();
- mutex_unlock(&swap_slots_cache_enable_mutex);
-}
-
-static bool check_cache_active(void)
-{
- long pages;
-
- if (!swap_slot_cache_enabled)
- return false;
-
- pages = get_nr_swap_pages();
- if (!swap_slot_cache_active) {
- if (pages > num_online_cpus() *
- THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE)
- reactivate_swap_slots_cache();
- goto out;
- }
-
- /* if global pool of slot caches too low, deactivate cache */
- if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE)
- deactivate_swap_slots_cache();
-out:
- return swap_slot_cache_active;
-}
-
-static int alloc_swap_slot_cache(unsigned int cpu)
-{
- struct swap_slots_cache *cache;
- swp_entry_t *slots;
-
- /*
- * Do allocation outside swap_slots_cache_mutex
- * as kvzalloc could trigger reclaim and folio_alloc_swap,
- * which can lock swap_slots_cache_mutex.
- */
- slots = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
- GFP_KERNEL);
- if (!slots)
- return -ENOMEM;
-
- mutex_lock(&swap_slots_cache_mutex);
- cache = &per_cpu(swp_slots, cpu);
- if (cache->slots) {
- /* cache already allocated */
- mutex_unlock(&swap_slots_cache_mutex);
-
- kvfree(slots);
-
- return 0;
- }
-
- if (!cache->lock_initialized) {
- mutex_init(&cache->alloc_lock);
- cache->lock_initialized = true;
- }
- cache->nr = 0;
- cache->cur = 0;
- cache->n_ret = 0;
- /*
- * We initialized alloc_lock and free_lock earlier. We use
- * !cache->slots or !cache->slots_ret to know if it is safe to acquire
- * the corresponding lock and use the cache. Memory barrier below
- * ensures the assumption.
- */
- mb();
- cache->slots = slots;
- mutex_unlock(&swap_slots_cache_mutex);
- return 0;
-}
-
-static void drain_slots_cache_cpu(unsigned int cpu, bool free_slots)
-{
- struct swap_slots_cache *cache;
-
- cache = &per_cpu(swp_slots, cpu);
- if (cache->slots) {
- mutex_lock(&cache->alloc_lock);
- swapcache_free_entries(cache->slots + cache->cur, cache->nr);
- cache->cur = 0;
- cache->nr = 0;
- if (free_slots && cache->slots) {
- kvfree(cache->slots);
- cache->slots = NULL;
- }
- mutex_unlock(&cache->alloc_lock);
- }
-}
-
-static void __drain_swap_slots_cache(void)
-{
- unsigned int cpu;
-
- /*
- * This function is called during
- * 1) swapoff, when we have to make sure no
- * left over slots are in cache when we remove
- * a swap device;
- * 2) disabling of swap slot cache, when we run low
- * on swap slots when allocating memory and need
- * to return swap slots to global pool.
- *
- * We cannot acquire cpu hot plug lock here as
- * this function can be invoked in the cpu
- * hot plug path:
- * cpu_up -> lock cpu_hotplug -> cpu hotplug state callback
- * -> memory allocation -> direct reclaim -> folio_alloc_swap
- * -> drain_swap_slots_cache
- *
- * Hence the loop over current online cpu below could miss cpu that
- * is being brought online but not yet marked as online.
- * That is okay as we do not schedule and run anything on a
- * cpu before it has been marked online. Hence, we will not
- * fill any swap slots in slots cache of such cpu.
- * There are no slots on such cpu that need to be drained.
- */
- for_each_online_cpu(cpu)
- drain_slots_cache_cpu(cpu, false);
-}
-
-static int free_slot_cache(unsigned int cpu)
-{
- mutex_lock(&swap_slots_cache_mutex);
- drain_slots_cache_cpu(cpu, true);
- mutex_unlock(&swap_slots_cache_mutex);
- return 0;
-}
-
-void enable_swap_slots_cache(void)
-{
- mutex_lock(&swap_slots_cache_enable_mutex);
- if (!swap_slot_cache_initialized) {
- int ret;
-
- ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
- alloc_swap_slot_cache, free_slot_cache);
- if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
- "without swap slots cache.\n", __func__))
- goto out_unlock;
-
- swap_slot_cache_initialized = true;
- }
-
- __reenable_swap_slots_cache();
-out_unlock:
- mutex_unlock(&swap_slots_cache_enable_mutex);
-}
-
-/* called with swap slot cache's alloc lock held */
-static int refill_swap_slots_cache(struct swap_slots_cache *cache)
-{
- if (!use_swap_slot_cache)
- return 0;
-
- cache->cur = 0;
- if (swap_slot_cache_active)
- cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE,
- cache->slots, 0);
-
- return cache->nr;
-}
-
-swp_entry_t folio_alloc_swap(struct folio *folio)
-{
- swp_entry_t entry;
- struct swap_slots_cache *cache;
-
- entry.val = 0;
-
- if (folio_test_large(folio)) {
- if (IS_ENABLED(CONFIG_THP_SWAP))
- get_swap_pages(1, &entry, folio_order(folio));
- goto out;
- }
-
- /*
- * Preemption is allowed here, because we may sleep
- * in refill_swap_slots_cache(). But it is safe, because
- * accesses to the per-CPU data structure are protected by the
- * mutex cache->alloc_lock.
- *
- * The alloc path here does not touch cache->slots_ret
- * so cache->free_lock is not taken.
- */
- cache = raw_cpu_ptr(&swp_slots);
-
- if (likely(check_cache_active() && cache->slots)) {
- mutex_lock(&cache->alloc_lock);
- if (cache->slots) {
-repeat:
- if (cache->nr) {
- entry = cache->slots[cache->cur];
- cache->slots[cache->cur++].val = 0;
- cache->nr--;
- } else if (refill_swap_slots_cache(cache)) {
- goto repeat;
- }
- }
- mutex_unlock(&cache->alloc_lock);
- if (entry.val)
- goto out;
- }
-
- get_swap_pages(1, &entry, 0);
-out:
- if (mem_cgroup_try_charge_swap(folio, entry)) {
- put_swap_folio(folio, entry);
- entry.val = 0;
- }
- return entry;
-}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 50840a2887a5..2b5744e211cd 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -20,7 +20,6 @@
#include <linux/blkdev.h>
#include <linux/migrate.h>
#include <linux/vmalloc.h>
-#include <linux/swap_slots.h>
#include <linux/huge_mm.h>
#include <linux/shmem_fs.h>
#include "internal.h"
@@ -447,13 +446,8 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
/*
* Just skip read ahead for unused swap slot.
- * During swap_off when swap_slot_cache is disabled,
- * we have to handle the race between putting
- * swap entry in swap cache and marking swap slot
- * as SWAP_HAS_CACHE. That's done in later part of code or
- * else swap_off will be aborted if we return NULL.
*/
- if (!swap_entry_swapped(si, entry) && swap_slot_cache_enabled)
+ if (!swap_entry_swapped(si, entry))
goto put_and_return;
/*
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 7caaaea95408..1ba916109d99 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -37,7 +37,6 @@
#include <linux/oom.h>
#include <linux/swapfile.h>
#include <linux/export.h>
-#include <linux/swap_slots.h>
#include <linux/sort.h>
#include <linux/completion.h>
#include <linux/suspend.h>
@@ -885,6 +884,13 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
struct swap_cluster_info *ci;
unsigned int offset, found = 0;
+ /*
+ * Swapfile is not block device so unable
+ * to allocate large entries.
+ */
+ if (order && !(si->flags & SWP_BLKDEV))
+ return 0;
+
if (!(si->flags & SWP_SOLIDSTATE)) {
/* Serialize HDD SWAP allocation for each device. */
spin_lock(&si->global_cluster_lock);
@@ -1148,43 +1154,6 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
swap_usage_sub(si, nr_entries);
}
-static int scan_swap_map_slots(struct swap_info_struct *si,
- unsigned char usage, int nr,
- swp_entry_t slots[], int order)
-{
- unsigned int nr_pages = 1 << order;
- int n_ret = 0;
-
- if (order > 0) {
- /*
- * Should not even be attempting large allocations when huge
- * page swap is disabled. Warn and fail the allocation.
- */
- if (!IS_ENABLED(CONFIG_THP_SWAP) ||
- nr_pages > SWAPFILE_CLUSTER) {
- VM_WARN_ON_ONCE(1);
- return 0;
- }
-
- /*
- * Swapfile is not block device so unable
- * to allocate large entries.
- */
- if (!(si->flags & SWP_BLKDEV))
- return 0;
- }
-
- while (n_ret < nr) {
- unsigned long offset = cluster_alloc_swap_entry(si, order, usage);
-
- if (!offset)
- break;
- slots[n_ret++] = swp_entry(si->type, offset);
- }
-
- return n_ret;
-}
-
static bool get_swap_device_info(struct swap_info_struct *si)
{
if (!percpu_ref_tryget_live(&si->users))
@@ -1205,16 +1174,13 @@ static bool get_swap_device_info(struct swap_info_struct *si)
* Fast path try to get swap entries with specified order from current
* CPU's swap entry pool (a cluster).
*/
-static int swap_alloc_fast(swp_entry_t entries[],
+static int swap_alloc_fast(swp_entry_t *entry,
unsigned char usage,
- int order, int n_goal)
+ int order)
{
struct swap_cluster_info *ci;
struct swap_info_struct *si;
- unsigned int offset, found;
- int n_ret = 0;
-
- n_goal = min(n_goal, SWAP_BATCH);
+ unsigned int offset, found = SWAP_ENTRY_INVALID;
/*
* Once allocated, swap_info_struct will never be completely freed,
@@ -1223,44 +1189,48 @@ static int swap_alloc_fast(swp_entry_t entries[],
si = __this_cpu_read(percpu_swap_cluster.si[order]);
offset = __this_cpu_read(percpu_swap_cluster.offset[order]);
if (!si || !offset || !get_swap_device_info(si))
- return 0;
+ return false;
- while (offset) {
- ci = lock_cluster(si, offset);
- if (!cluster_is_usable(ci, order))
- break;
+ ci = lock_cluster(si, offset);
+ if (cluster_is_usable(ci, order)) {
if (cluster_is_empty(ci))
offset = cluster_offset(si, ci);
found = alloc_swap_scan_cluster(si, ci, offset, order, usage);
- if (!found)
- break;
- entries[n_ret++] = swp_entry(si->type, found);
- if (n_ret == n_goal)
- break;
- offset = __this_cpu_read(percpu_swap_cluster.offset[order]);
+ if (found)
+ *entry = swp_entry(si->type, found);
+ } else {
+ unlock_cluster(ci);
}
put_swap_device(si);
- return n_ret;
+ return !!found;
}
-int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
+swp_entry_t folio_alloc_swap(struct folio *folio)
{
- int order = swap_entry_order(entry_order);
- unsigned long size = 1 << order;
+ unsigned int order = folio_order(folio);
+ unsigned int size = 1 << order;
struct swap_info_struct *si, *next;
- int n_ret = 0;
+ swp_entry_t entry = {};
+ unsigned long offset;
int node;
+ if (order) {
+ /*
+ * Should not even be attempting large allocations when huge
+ * page swap is disabled. Warn and fail the allocation.
+ */
+ if (!IS_ENABLED(CONFIG_THP_SWAP) || size > SWAPFILE_CLUSTER) {
+ VM_WARN_ON_ONCE(1);
+ return entry;
+ }
+ }
+
/* Fast path using percpu cluster */
local_lock(&percpu_swap_cluster.lock);
- n_ret = swap_alloc_fast(swp_entries,
- SWAP_HAS_CACHE,
- order, n_goal);
- if (n_ret == n_goal)
- goto out;
+ if (swap_alloc_fast(&entry, SWAP_HAS_CACHE, order))
+ goto out_alloced;
- n_goal = min_t(int, n_goal - n_ret, SWAP_BATCH);
/* Rotate the device and switch to a new cluster */
spin_lock(&swap_avail_lock);
start_over:
@@ -1269,19 +1239,14 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
spin_unlock(&swap_avail_lock);
if (get_swap_device_info(si)) {
- /*
- * For order 0 allocation, try best to fill the request
- * as it's used by slot cache.
- *
- * For mTHP allocation, it always have n_goal == 1,
- * and falling a mTHP swapin will just make the caller
- * fallback to order 0 allocation, so just bail out.
- */
- n_ret += scan_swap_map_slots(si, SWAP_HAS_CACHE, n_goal,
- swp_entries + n_ret, order);
+ offset = cluster_alloc_swap_entry(si, order, SWAP_HAS_CACHE);
put_swap_device(si);
- if (n_ret || size > 1)
- goto out;
+ if (offset) {
+ entry = swp_entry(si->type, offset);
+ goto out_alloced;
+ }
+ if (order)
+ goto out_failed;
}
spin_lock(&swap_avail_lock);
@@ -1300,10 +1265,20 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
goto start_over;
}
spin_unlock(&swap_avail_lock);
-out:
+out_failed:
+ local_unlock(&percpu_swap_cluster.lock);
+ return entry;
+
+out_alloced:
local_unlock(&percpu_swap_cluster.lock);
- atomic_long_sub(n_ret * size, &nr_swap_pages);
- return n_ret;
+ if (mem_cgroup_try_charge_swap(folio, entry)) {
+ put_swap_folio(folio, entry);
+ entry.val = 0;
+ } else {
+ atomic_long_sub(size, &nr_swap_pages);
+ }
+
+ return entry;
}
static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
@@ -1599,25 +1574,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
unlock_cluster(ci);
}
-void swapcache_free_entries(swp_entry_t *entries, int n)
-{
- int i;
- struct swap_cluster_info *ci;
- struct swap_info_struct *si = NULL;
-
- if (n <= 0)
- return;
-
- for (i = 0; i < n; ++i) {
- si = _swap_info_get(entries[i]);
- if (si) {
- ci = lock_cluster(si, swp_offset(entries[i]));
- swap_entry_range_free(si, ci, entries[i], 1);
- unlock_cluster(ci);
- }
- }
-}
-
int __swap_count(swp_entry_t entry)
{
struct swap_info_struct *si = swp_swap_info(entry);
@@ -1858,6 +1814,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr)
swp_entry_t get_swap_page_of_type(int type)
{
struct swap_info_struct *si = swap_type_to_swap_info(type);
+ unsigned long offset;
swp_entry_t entry = {0};
if (!si)
@@ -1865,8 +1822,13 @@ swp_entry_t get_swap_page_of_type(int type)
/* This is called for allocating swap entry, not cache */
if (get_swap_device_info(si)) {
- if ((si->flags & SWP_WRITEOK) && scan_swap_map_slots(si, 1, 1, &entry, 0))
- atomic_long_dec(&nr_swap_pages);
+ if (si->flags & SWP_WRITEOK) {
+ offset = cluster_alloc_swap_entry(si, 0, 1);
+ if (offset) {
+ entry = swp_entry(si->type, offset);
+ atomic_long_dec(&nr_swap_pages);
+ }
+ }
put_swap_device(si);
}
fail:
@@ -2627,21 +2589,6 @@ static void reinsert_swap_info(struct swap_info_struct *si)
spin_unlock(&swap_lock);
}
-static bool __has_usable_swap(void)
-{
- return !plist_head_empty(&swap_active_head);
-}
-
-bool has_usable_swap(void)
-{
- bool ret;
-
- spin_lock(&swap_lock);
- ret = __has_usable_swap();
- spin_unlock(&swap_lock);
- return ret;
-}
-
/*
* Called after clearing SWP_WRITEOK, ensures cluster_alloc_range
* see the updated flags, so there will be no more allocations.
@@ -2732,8 +2679,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
wait_for_allocation(p);
- disable_swap_slots_cache_lock();
-
set_current_oom_origin();
err = try_to_unuse(p->type);
clear_current_oom_origin();
@@ -2741,12 +2686,9 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
if (err) {
/* re-insert swap space back into swap_list */
reinsert_swap_info(p);
- reenable_swap_slots_cache_unlock();
goto out_dput;
}
- reenable_swap_slots_cache_unlock();
-
/*
* Wait for swap operations protected by get/put_swap_device()
* to complete. Because of synchronize_rcu() here, all swap
@@ -3495,8 +3437,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
putname(name);
if (inode)
inode_unlock(inode);
- if (!error)
- enable_swap_slots_cache();
return error;
}
@@ -3892,6 +3832,11 @@ static void free_swap_count_continuations(struct swap_info_struct *si)
}
#if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
+static bool __has_usable_swap(void)
+{
+ return !plist_head_empty(&swap_active_head);
+}
+
void __folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
{
struct swap_info_struct *si, *next;
--
2.48.1
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH v2 6/7] mm, swap: remove swap slot cache
2025-02-24 18:02 ` [PATCH v2 6/7] mm, swap: remove swap slot cache Kairui Song
@ 2025-02-25 6:39 ` Baoquan He
0 siblings, 0 replies; 14+ messages in thread
From: Baoquan He @ 2025-02-25 6:39 UTC (permalink / raw)
To: Kairui Song
Cc: linux-mm, Andrew Morton, Chris Li, Barry Song, Hugh Dickins,
Yosry Ahmed, Huang, Ying, Nhat Pham, Johannes Weiner,
Baolin Wang, Kalesh Singh, Matthew Wilcox, linux-kernel
On 02/25/25 at 02:02am, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
>
> Slot cache is no longer needed now, removing it and all related code.
>
> - vm-scalability with: `usemem --init-time -O -y -x -R -31 1G`,
> 12G memory cgroup using simulated pmem as SWAP (32G pmem, 32 CPUs),
> 16 test runs for each case, measuring the total throughput:
>
> Before (KB/s) (stdev) After (KB/s) (stdev)
> Random (4K): 424907.60 (24410.78) 414745.92 (34554.78)
> Random (64K): 163308.82 (11635.72) 167314.50 (18434.99)
> Sequential (4K, !-R): 6150056.79 (103205.90) 6321469.06 (115878.16)
>
> The performance changes are below noise level.
>
> - Build linux kernel with make -j96, using 4K folio with 1.5G memory
> cgroup limit and 64K folio with 2G memory cgroup limit, on top of tmpfs,
> 12 test runs, measuring the system time:
>
> Before (s) (stdev) After (s) (stdev)
> make -j96 (4K): 6445.69 (61.95) 6408.80 (69.46)
> make -j96 (64K): 6841.71 (409.04) 6437.99 (435.55)
>
> Similar to above, 64k mTHP case showed a slight improvement.
>
> Signed-off-by: Kairui Song <kasong@tencent.com>
> ---
> include/linux/swap.h | 2 -
> include/linux/swap_slots.h | 28 ----
> mm/Makefile | 2 +-
> mm/swap_slots.c | 295 -------------------------------------
> mm/swap_state.c | 8 +-
> mm/swapfile.c | 193 +++++++++---------------
> 6 files changed, 71 insertions(+), 457 deletions(-)
> delete mode 100644 include/linux/swap_slots.h
> delete mode 100644 mm/swap_slots.c
Reviewed-by: Baoquan He <bhe@redhat.com>
^ permalink raw reply [flat|nested] 14+ messages in thread
* [PATCH v2 7/7] mm, swap: simplify folio swap allocation
2025-02-24 18:02 [PATCH v2 0/7] mm, swap: remove swap slot cache Kairui Song
` (5 preceding siblings ...)
2025-02-24 18:02 ` [PATCH v2 6/7] mm, swap: remove swap slot cache Kairui Song
@ 2025-02-24 18:02 ` Kairui Song
2025-02-25 6:43 ` Baoquan He
6 siblings, 1 reply; 14+ messages in thread
From: Kairui Song @ 2025-02-24 18:02 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Chris Li, Barry Song, Hugh Dickins, Yosry Ahmed,
Huang, Ying, Baoquan He, Nhat Pham, Johannes Weiner, Baolin Wang,
Kalesh Singh, Matthew Wilcox, linux-kernel, Kairui Song
From: Kairui Song <kasong@tencent.com>
With slot cache gone, clean up the allocation helpers even more.
folio_alloc_swap will be the only entry for allocation and adding
the folio to swap cache (except suspend), making it opposite of
folio_free_swap.
Signed-off-by: Kairui Song <kasong@tencent.com>
---
include/linux/swap.h | 8 ++--
mm/shmem.c | 21 +++------
mm/swap.h | 6 ---
mm/swap_state.c | 57 ----------------------
mm/swapfile.c | 110 ++++++++++++++++++++++++++++---------------
mm/vmscan.c | 16 ++++++-
6 files changed, 94 insertions(+), 124 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index a0a262bcaf41..3a68da686c4e 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -478,7 +478,7 @@ static inline long get_nr_swap_pages(void)
}
extern void si_swapinfo(struct sysinfo *);
-swp_entry_t folio_alloc_swap(struct folio *folio);
+int folio_alloc_swap(struct folio *folio, gfp_t gfp_mask);
bool folio_free_swap(struct folio *folio);
void put_swap_folio(struct folio *folio, swp_entry_t entry);
extern swp_entry_t get_swap_page_of_type(int);
@@ -587,11 +587,9 @@ static inline int swp_swapcount(swp_entry_t entry)
return 0;
}
-static inline swp_entry_t folio_alloc_swap(struct folio *folio)
+static int folio_alloc_swap(struct folio *folio, gfp_t gfp_mask)
{
- swp_entry_t entry;
- entry.val = 0;
- return entry;
+ return -EINVAL;
}
static inline bool folio_free_swap(struct folio *folio)
diff --git a/mm/shmem.c b/mm/shmem.c
index 45dbcb69da0c..aad02132b75a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1546,7 +1546,6 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
struct inode *inode = mapping->host;
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
- swp_entry_t swap;
pgoff_t index;
int nr_pages;
bool split = false;
@@ -1628,14 +1627,6 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
folio_mark_uptodate(folio);
}
- swap = folio_alloc_swap(folio);
- if (!swap.val) {
- if (nr_pages > 1)
- goto try_split;
-
- goto redirty;
- }
-
/*
* Add inode to shmem_unuse()'s list of swapped-out inodes,
* if it's not already there. Do it now before the folio is
@@ -1648,20 +1639,20 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
if (list_empty(&info->swaplist))
list_add(&info->swaplist, &shmem_swaplist);
- if (add_to_swap_cache(folio, swap,
- __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN,
- NULL) == 0) {
+ if (!folio_alloc_swap(folio, __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN)) {
shmem_recalc_inode(inode, 0, nr_pages);
- swap_shmem_alloc(swap, nr_pages);
- shmem_delete_from_page_cache(folio, swp_to_radix_entry(swap));
+ swap_shmem_alloc(folio->swap, nr_pages);
+ shmem_delete_from_page_cache(folio, swp_to_radix_entry(folio->swap));
mutex_unlock(&shmem_swaplist_mutex);
BUG_ON(folio_mapped(folio));
return swap_writepage(&folio->page, wbc);
}
+ list_del_init(&info->swaplist);
mutex_unlock(&shmem_swaplist_mutex);
- put_swap_folio(folio, swap);
+ if (nr_pages > 1)
+ goto try_split;
redirty:
folio_mark_dirty(folio);
if (wbc->for_reclaim)
diff --git a/mm/swap.h b/mm/swap.h
index ad2f121de970..0abb68091b4f 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -50,7 +50,6 @@ static inline pgoff_t swap_cache_index(swp_entry_t entry)
}
void show_swap_cache_info(void);
-bool add_to_swap(struct folio *folio);
void *get_shadow_from_swap_cache(swp_entry_t entry);
int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
gfp_t gfp, void **shadowp);
@@ -163,11 +162,6 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping,
return filemap_get_folio(mapping, index);
}
-static inline bool add_to_swap(struct folio *folio)
-{
- return false;
-}
-
static inline void *get_shadow_from_swap_cache(swp_entry_t entry)
{
return NULL;
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 2b5744e211cd..68fd981b514f 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -166,63 +166,6 @@ void __delete_from_swap_cache(struct folio *folio,
__lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr);
}
-/**
- * add_to_swap - allocate swap space for a folio
- * @folio: folio we want to move to swap
- *
- * Allocate swap space for the folio and add the folio to the
- * swap cache.
- *
- * Context: Caller needs to hold the folio lock.
- * Return: Whether the folio was added to the swap cache.
- */
-bool add_to_swap(struct folio *folio)
-{
- swp_entry_t entry;
- int err;
-
- VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
- VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
-
- entry = folio_alloc_swap(folio);
- if (!entry.val)
- return false;
-
- /*
- * XArray node allocations from PF_MEMALLOC contexts could
- * completely exhaust the page allocator. __GFP_NOMEMALLOC
- * stops emergency reserves from being allocated.
- *
- * TODO: this could cause a theoretical memory reclaim
- * deadlock in the swap out path.
- */
- /*
- * Add it to the swap cache.
- */
- err = add_to_swap_cache(folio, entry,
- __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
- if (err)
- goto fail;
- /*
- * Normally the folio will be dirtied in unmap because its
- * pte should be dirty. A special case is MADV_FREE page. The
- * page's pte could have dirty bit cleared but the folio's
- * SwapBacked flag is still set because clearing the dirty bit
- * and SwapBacked flag has no lock protected. For such folio,
- * unmap will not set dirty bit for it, so folio reclaim will
- * not write the folio out. This can cause data corruption when
- * the folio is swapped in later. Always setting the dirty flag
- * for the folio solves the problem.
- */
- folio_mark_dirty(folio);
-
- return true;
-
-fail:
- put_swap_folio(folio, entry);
- return false;
-}
-
/*
* This must be called only on folios that have
* been verified to be in the swap cache and locked.
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1ba916109d99..628f67974a7c 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1174,9 +1174,9 @@ static bool get_swap_device_info(struct swap_info_struct *si)
* Fast path try to get swap entries with specified order from current
* CPU's swap entry pool (a cluster).
*/
-static int swap_alloc_fast(swp_entry_t *entry,
- unsigned char usage,
- int order)
+static bool swap_alloc_fast(swp_entry_t *entry,
+ unsigned char usage,
+ int order)
{
struct swap_cluster_info *ci;
struct swap_info_struct *si;
@@ -1206,47 +1206,31 @@ static int swap_alloc_fast(swp_entry_t *entry,
return !!found;
}
-swp_entry_t folio_alloc_swap(struct folio *folio)
+/* Rotate the device and switch to a new cluster */
+static bool swap_alloc_slow(swp_entry_t *entry,
+ unsigned char usage,
+ int order)
{
- unsigned int order = folio_order(folio);
- unsigned int size = 1 << order;
- struct swap_info_struct *si, *next;
- swp_entry_t entry = {};
- unsigned long offset;
int node;
+ unsigned long offset;
+ struct swap_info_struct *si, *next;
- if (order) {
- /*
- * Should not even be attempting large allocations when huge
- * page swap is disabled. Warn and fail the allocation.
- */
- if (!IS_ENABLED(CONFIG_THP_SWAP) || size > SWAPFILE_CLUSTER) {
- VM_WARN_ON_ONCE(1);
- return entry;
- }
- }
-
- /* Fast path using percpu cluster */
- local_lock(&percpu_swap_cluster.lock);
- if (swap_alloc_fast(&entry, SWAP_HAS_CACHE, order))
- goto out_alloced;
-
- /* Rotate the device and switch to a new cluster */
+ node = numa_node_id();
spin_lock(&swap_avail_lock);
start_over:
- node = numa_node_id();
plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
+ /* Rotate the device and switch to a new cluster */
plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
spin_unlock(&swap_avail_lock);
if (get_swap_device_info(si)) {
offset = cluster_alloc_swap_entry(si, order, SWAP_HAS_CACHE);
put_swap_device(si);
if (offset) {
- entry = swp_entry(si->type, offset);
- goto out_alloced;
+ *entry = swp_entry(si->type, offset);
+ return true;
}
if (order)
- goto out_failed;
+ return false;
}
spin_lock(&swap_avail_lock);
@@ -1265,20 +1249,68 @@ swp_entry_t folio_alloc_swap(struct folio *folio)
goto start_over;
}
spin_unlock(&swap_avail_lock);
-out_failed:
+ return false;
+}
+
+/**
+ * folio_alloc_swap - allocate swap space for a folio
+ * @folio: folio we want to move to swap
+ * @gfp: gfp mask for shadow nodes
+ *
+ * Allocate swap space for the folio and add the folio to the
+ * swap cache.
+ *
+ * Context: Caller needs to hold the folio lock.
+ * Return: Whether the folio was added to the swap cache.
+ */
+int folio_alloc_swap(struct folio *folio, gfp_t gfp)
+{
+ unsigned int order = folio_order(folio);
+ unsigned int size = 1 << order;
+ swp_entry_t entry = {};
+
+ VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+ VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
+
+ /*
+ * Should not even be attempting large allocations when huge
+ * page swap is disabled. Warn and fail the allocation.
+ */
+ if (order && (!IS_ENABLED(CONFIG_THP_SWAP) || size > SWAPFILE_CLUSTER)) {
+ VM_WARN_ON_ONCE(1);
+ return -EINVAL;
+ }
+
+ local_lock(&percpu_swap_cluster.lock);
+ if (swap_alloc_fast(&entry, SWAP_HAS_CACHE, order))
+ goto out_alloced;
+ if (swap_alloc_slow(&entry, SWAP_HAS_CACHE, order))
+ goto out_alloced;
local_unlock(&percpu_swap_cluster.lock);
- return entry;
+ return -ENOMEM;
out_alloced:
local_unlock(&percpu_swap_cluster.lock);
- if (mem_cgroup_try_charge_swap(folio, entry)) {
- put_swap_folio(folio, entry);
- entry.val = 0;
- } else {
- atomic_long_sub(size, &nr_swap_pages);
- }
+ if (mem_cgroup_try_charge_swap(folio, entry))
+ goto out_free;
- return entry;
+ /*
+ * XArray node allocations from PF_MEMALLOC contexts could
+ * completely exhaust the page allocator. __GFP_NOMEMALLOC
+ * stops emergency reserves from being allocated.
+ *
+ * TODO: this could cause a theoretical memory reclaim
+ * deadlock in the swap out path.
+ */
+ if (add_to_swap_cache(folio, entry, gfp | __GFP_NOMEMALLOC, NULL))
+ goto out_free;
+
+ atomic_long_sub(size, &nr_swap_pages);
+ return 0;
+
+out_free:
+ put_swap_folio(folio, entry);
+ return -ENOMEM;
}
static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index fcca38bc640f..be00af3763b5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1289,7 +1289,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
split_folio_to_list(folio, folio_list))
goto activate_locked;
}
- if (!add_to_swap(folio)) {
+ if (folio_alloc_swap(folio, __GFP_HIGH | __GFP_NOWARN)) {
int __maybe_unused order = folio_order(folio);
if (!folio_test_large(folio))
@@ -1305,9 +1305,21 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
}
#endif
count_mthp_stat(order, MTHP_STAT_SWPOUT_FALLBACK);
- if (!add_to_swap(folio))
+ if (folio_alloc_swap(folio, __GFP_HIGH | __GFP_NOWARN))
goto activate_locked_split;
}
+ /*
+ * Normally the folio will be dirtied in unmap because its
+ * pte should be dirty. A special case is MADV_FREE page. The
+ * page's pte could have dirty bit cleared but the folio's
+ * SwapBacked flag is still set because clearing the dirty bit
+ * and SwapBacked flag has no lock protected. For such folio,
+ * unmap will not set dirty bit for it, so folio reclaim will
+ * not write the folio out. This can cause data corruption when
+ * the folio is swapped in later. Always setting the dirty flag
+ * for the folio solves the problem.
+ */
+ folio_mark_dirty(folio);
}
}
--
2.48.1
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH v2 7/7] mm, swap: simplify folio swap allocation
2025-02-24 18:02 ` [PATCH v2 7/7] mm, swap: simplify folio swap allocation Kairui Song
@ 2025-02-25 6:43 ` Baoquan He
0 siblings, 0 replies; 14+ messages in thread
From: Baoquan He @ 2025-02-25 6:43 UTC (permalink / raw)
To: Kairui Song
Cc: linux-mm, Andrew Morton, Chris Li, Barry Song, Hugh Dickins,
Yosry Ahmed, Huang, Ying, Nhat Pham, Johannes Weiner,
Baolin Wang, Kalesh Singh, Matthew Wilcox, linux-kernel
On 02/25/25 at 02:02am, Kairui Song wrote:
......snip...
> @@ -1265,20 +1249,68 @@ swp_entry_t folio_alloc_swap(struct folio *folio)
> goto start_over;
> }
> spin_unlock(&swap_avail_lock);
> -out_failed:
> + return false;
> +}
> +
> +/**
> + * folio_alloc_swap - allocate swap space for a folio
> + * @folio: folio we want to move to swap
> + * @gfp: gfp mask for shadow nodes
> + *
> + * Allocate swap space for the folio and add the folio to the
> + * swap cache.
> + *
> + * Context: Caller needs to hold the folio lock.
> + * Return: Whether the folio was added to the swap cache.
If only returning on whether folio being added or not, it's better to
return bool value for now. Anyway, this is trivial. This whole
patch looks good to me.
Reviewed-by: Baoquan He <bhe@redhat.com>
> + */
> +int folio_alloc_swap(struct folio *folio, gfp_t gfp)
> +{
> + unsigned int order = folio_order(folio);
> + unsigned int size = 1 << order;
> + swp_entry_t entry = {};
> +
> + VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
> + VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
> +
> + /*
> + * Should not even be attempting large allocations when huge
> + * page swap is disabled. Warn and fail the allocation.
> + */
> + if (order && (!IS_ENABLED(CONFIG_THP_SWAP) || size > SWAPFILE_CLUSTER)) {
> + VM_WARN_ON_ONCE(1);
> + return -EINVAL;
> + }
> +
> + local_lock(&percpu_swap_cluster.lock);
> + if (swap_alloc_fast(&entry, SWAP_HAS_CACHE, order))
> + goto out_alloced;
> + if (swap_alloc_slow(&entry, SWAP_HAS_CACHE, order))
> + goto out_alloced;
> local_unlock(&percpu_swap_cluster.lock);
> - return entry;
> + return -ENOMEM;
>
> out_alloced:
> local_unlock(&percpu_swap_cluster.lock);
> - if (mem_cgroup_try_charge_swap(folio, entry)) {
> - put_swap_folio(folio, entry);
> - entry.val = 0;
> - } else {
> - atomic_long_sub(size, &nr_swap_pages);
> - }
> + if (mem_cgroup_try_charge_swap(folio, entry))
> + goto out_free;
>
> - return entry;
> + /*
> + * XArray node allocations from PF_MEMALLOC contexts could
> + * completely exhaust the page allocator. __GFP_NOMEMALLOC
> + * stops emergency reserves from being allocated.
> + *
> + * TODO: this could cause a theoretical memory reclaim
> + * deadlock in the swap out path.
> + */
> + if (add_to_swap_cache(folio, entry, gfp | __GFP_NOMEMALLOC, NULL))
> + goto out_free;
> +
> + atomic_long_sub(size, &nr_swap_pages);
> + return 0;
> +
> +out_free:
> + put_swap_folio(folio, entry);
> + return -ENOMEM;
> }
>
> static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
....snip....
^ permalink raw reply [flat|nested] 14+ messages in thread