[PATCH v2 20/32] mm/madvise: clean up pte_offset_map_lock() scans

Hugh Dickins
2023-06-09T01:34:12Z

Came here to make madvise's several pte_offset_map_lock() scans advance
to next extent on failure, and remove superfluous pmd_trans_unstable()
and pmd_none_or_trans_huge_or_clear_bad() calls. But also did some
nearby cleanup.

swapin_walk_pmd_entry(): don't name an address "index"; don't drop the
lock after every pte, only when calling out to read_swap_cache_async().

madvise_cold_or_pageout_pte_range() and madvise_free_pte_range():
prefer "start_pte" for pointer, orig_pte usually denotes a saved pte
value; leave lazy MMU mode before unlocking; merge the success and
failure paths after split_folio().

Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/madvise.c | 122 ++++++++++++++++++++++++++++-----------------------
1 file changed, 68 insertions(+), 54 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index b5ffbaf616f5..0af64c4a8f82 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -188,37 +188,43 @@ static int madvise_update_vma(struct vm_area_struct *vma,

#ifdef CONFIG_SWAP
static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
- unsigned long end, struct mm_walk *walk)
+ unsigned long end, struct mm_walk *walk)
{
struct vm_area_struct *vma = walk->private;
- unsigned long index;
struct swap_iocb *splug = NULL;
+ pte_t *ptep = NULL;
+ spinlock_t *ptl;
+ unsigned long addr;

- if (pmd_none_or_trans_huge_or_clear_bad(pmd))
- return 0;
-
- for (index = start; index != end; index += PAGE_SIZE) {
+ for (addr = start; addr < end; addr += PAGE_SIZE) {
pte_t pte;
swp_entry_t entry;
struct page *page;
- spinlock_t *ptl;
- pte_t *ptep;

- ptep = pte_offset_map_lock(vma->vm_mm, pmd, index, &ptl);
+ if (!ptep++) {
+ ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ if (!ptep)
+ break;
+ }
+
pte = *ptep;
- pte_unmap_unlock(ptep, ptl);
-
if (!is_swap_pte(pte))
continue;
entry = pte_to_swp_entry(pte);
if (unlikely(non_swap_entry(entry)))
continue;

+ pte_unmap_unlock(ptep, ptl);
+ ptep = NULL;
+
page = read_swap_cache_async(entry, GFP_HIGHUSER_MOVABLE,
- vma, index, false, &splug);
+ vma, addr, false, &splug);
if (page)
put_page(page);
}
+
+ if (ptep)
+ pte_unmap_unlock(ptep, ptl);
swap_read_unplug(splug);
cond_resched();

@@ -340,7 +346,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
bool pageout = private->pageout;
struct mm_struct *mm = tlb->mm;
struct vm_area_struct *vma = walk->vma;
- pte_t *orig_pte, *pte, ptent;
+ pte_t *start_pte, *pte, ptent;
spinlock_t *ptl;
struct folio *folio = NULL;
LIST_HEAD(folio_list);
@@ -422,11 +428,11 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
}

regular_folio:
- if (pmd_trans_unstable(pmd))
- return 0;
#endif
tlb_change_page_size(tlb, PAGE_SIZE);
- orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ if (!start_pte)
+ return 0;
flush_tlb_batched_pending(mm);
arch_enter_lazy_mmu_mode();
for (; addr < end; pte++, addr += PAGE_SIZE) {
@@ -447,25 +453,28 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
* are sure it's worth. Split it if we are only owner.
*/
if (folio_test_large(folio)) {
+ int err;
+
if (folio_mapcount(folio) != 1)
break;
if (pageout_anon_only_filter && !folio_test_anon(folio))
break;
+ if (!folio_trylock(folio))
+ break;
folio_get(folio);
- if (!folio_trylock(folio)) {
- folio_put(folio);
- break;
- }
- pte_unmap_unlock(orig_pte, ptl);
- if (split_folio(folio)) {
- folio_unlock(folio);
- folio_put(folio);
- orig_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
- break;
- }
+ arch_leave_lazy_mmu_mode();
+ pte_unmap_unlock(start_pte, ptl);
+ start_pte = NULL;
+ err = split_folio(folio);
folio_unlock(folio);
folio_put(folio);
- orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ if (err)
+ break;
+ start_pte = pte =
+ pte_offset_map_lock(mm, pmd, addr, &ptl);
+ if (!start_pte)
+ break;
+ arch_enter_lazy_mmu_mode();
pte--;
addr -= PAGE_SIZE;
continue;
@@ -510,8 +519,10 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
folio_deactivate(folio);
}

- arch_leave_lazy_mmu_mode();
- pte_unmap_unlock(orig_pte, ptl);
+ if (start_pte) {
+ arch_leave_lazy_mmu_mode();
+ pte_unmap_unlock(start_pte, ptl);
+ }
if (pageout)
reclaim_pages(&folio_list);
cond_resched();
@@ -612,7 +623,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
struct mm_struct *mm = tlb->mm;
struct vm_area_struct *vma = walk->vma;
spinlock_t *ptl;
- pte_t *orig_pte, *pte, ptent;
+ pte_t *start_pte, *pte, ptent;
struct folio *folio;
int nr_swap = 0;
unsigned long next;
@@ -620,13 +631,12 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
next = pmd_addr_end(addr, end);
if (pmd_trans_huge(*pmd))
if (madvise_free_huge_pmd(tlb, vma, pmd, addr, next))
- goto next;
-
- if (pmd_trans_unstable(pmd))
- return 0;
+ return 0;

tlb_change_page_size(tlb, PAGE_SIZE);
- orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ start_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ if (!start_pte)
+ return 0;
flush_tlb_batched_pending(mm);
arch_enter_lazy_mmu_mode();
for (; addr != end; pte++, addr += PAGE_SIZE) {
@@ -664,23 +674,26 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
* deactivate all pages.
*/
if (folio_test_large(folio)) {
+ int err;
+
if (folio_mapcount(folio) != 1)
- goto out;
+ break;
+ if (!folio_trylock(folio))
+ break;
folio_get(folio);
- if (!folio_trylock(folio)) {
- folio_put(folio);
- goto out;
- }
- pte_unmap_unlock(orig_pte, ptl);
- if (split_folio(folio)) {
- folio_unlock(folio);
- folio_put(folio);
- orig_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
- goto out;
- }
+ arch_leave_lazy_mmu_mode();
+ pte_unmap_unlock(start_pte, ptl);
+ start_pte = NULL;
+ err = split_folio(folio);
folio_unlock(folio);
folio_put(folio);
- orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ if (err)
+ break;
+ start_pte = pte =
+ pte_offset_map_lock(mm, pmd, addr, &ptl);
+ if (!start_pte)
+ break;
+ arch_enter_lazy_mmu_mode();
pte--;
addr -= PAGE_SIZE;
continue;
@@ -725,17 +738,18 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
}
folio_mark_lazyfree(folio);
}
-out:
+
if (nr_swap) {
if (current->mm == mm)
sync_mm_rss(mm);
-
add_mm_counter(mm, MM_SWAPENTS, nr_swap);
}
- arch_leave_lazy_mmu_mode();
- pte_unmap_unlock(orig_pte, ptl);
+ if (start_pte) {
+ arch_leave_lazy_mmu_mode();
+ pte_unmap_unlock(start_pte, ptl);
+ }
cond_resched();
-next:
+
return 0;
}

--
2.35.3