[PATCH 0/5] mm: swap: small fixes and comment cleanups

[PATCH 0/5] mm: swap: small fixes and comment cleanups

[Youngjun Park]

Hello,
This patch series contains small fixes and cleanups in the swap code.

It includes:
 - A memory leak fix on the error path
 - Minor logic adjustments
 - Removal of redundant or outdated comments

Thank you,
Youngjun Park
                                  
Youngjun Park (5):
  mm, swap: Fix memory leak in setup_clusters() error path
  mm, swap: Use SWP_SOLIDSTATE to determine if swap is rotational
  mm, swap: Remove redundant comment for read_swap_cache_async
  mm: swap: change swap_alloc_slow() to void
  mm: swap: remove scan_swap_map_slots() references from comments

 mm/swap_state.c |  4 ----
 mm/swapfile.c   | 35 ++++++++++++++++-------------------
 2 files changed, 16 insertions(+), 23 deletions(-)

base-commit: f30d294530d939fa4b77d61bc60f25c4284841fa (mm-new)
-- 
2.34.1

[PATCH 1/5] mm, swap: Fix memory leak in setup_clusters() error path

[Youngjun Park]

Some error path neglects to free the allocated 'cluster_info',
causing a memory leak.

Change the error jumps to the 'err_free' label to ensure proper
cleanup.

Fixes: 07adc4cf1ecd ("mm, swap: implement dynamic allocation of swap table")
Signed-off-by: Youngjun Park <youngjun.park@lge.com>
---
 mm/swapfile.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index c35bb8593f50..6dc0e7a738bc 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3339,7 +3339,7 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
 	 */
 	err = swap_cluster_setup_bad_slot(cluster_info, 0);
 	if (err)
-		goto err;
+		goto err_free;
 	for (i = 0; i < swap_header->info.nr_badpages; i++) {
 		unsigned int page_nr = swap_header->info.badpages[i];
 
@@ -3347,12 +3347,12 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
 			continue;
 		err = swap_cluster_setup_bad_slot(cluster_info, page_nr);
 		if (err)
-			goto err;
+			goto err_free;
 	}
 	for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++) {
 		err = swap_cluster_setup_bad_slot(cluster_info, i);
 		if (err)
-			goto err;
+			goto err_free;
 	}
 
 	INIT_LIST_HEAD(&si->free_clusters);
-- 
2.34.1

[PATCH 2/5] mm, swap: Use SWP_SOLIDSTATE to determine if swap is rotational

[Youngjun Park]

The current non rotational check is unreliable
as the device's rotational status can be changed by a user via sysfs.

Use the more reliable SWP_SOLIDSTATE flag which is set at swapon time,
to ensure the nr_rotate_swap count remains consistent.
Plus, it is easy to read and simple.

Signed-off-by: Youngjun Park <youngjun.park@lge.com>
---
 mm/swapfile.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6dc0e7a738bc..b5d42918c01b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2913,7 +2913,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	if (p->flags & SWP_CONTINUED)
 		free_swap_count_continuations(p);
 
-	if (!p->bdev || !bdev_nonrot(p->bdev))
+	if (!(p->flags & SWP_SOLIDSTATE))
 		atomic_dec(&nr_rotate_swap);
 
 	mutex_lock(&swapon_mutex);
-- 
2.34.1

[PATCH 3/5] mm, swap: Remove redundant comment for read_swap_cache_async

[Youngjun Park]

The function now manages get/put_swap_device() internally, making the
comment explaining this behavior to callers unnecessary.

Signed-off-by: Youngjun Park <youngjun.park@lge.com>
---
 mm/swap_state.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index b13e9c4baa90..d20d238109f9 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -509,10 +509,6 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
  * and reading the disk if it is not already cached.
  * A failure return means that either the page allocation failed or that
  * the swap entry is no longer in use.
- *
- * get/put_swap_device() aren't needed to call this function, because
- * __read_swap_cache_async() call them and swap_read_folio() holds the
- * swap cache folio lock.
  */
 struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 		struct vm_area_struct *vma, unsigned long addr,
-- 
2.34.1

[PATCH 4/5] mm: swap: change swap_alloc_slow() to void

[Youngjun Park]

swap_alloc_slow() does not need to return a bool, as all callers
handle allocation results via the entry parameter. Update the
function signature and remove return statements accordingly.

Signed-off-by: Youngjun Park <youngjun.park@lge.com>
---
 mm/swapfile.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index b5d42918c01b..89eb57eee7f7 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1339,7 +1339,7 @@ static bool swap_alloc_fast(swp_entry_t *entry,
 }
 
 /* Rotate the device and switch to a new cluster */
-static bool swap_alloc_slow(swp_entry_t *entry,
+static void swap_alloc_slow(swp_entry_t *entry,
 			    int order)
 {
 	unsigned long offset;
@@ -1356,10 +1356,10 @@ static bool swap_alloc_slow(swp_entry_t *entry,
 			put_swap_device(si);
 			if (offset) {
 				*entry = swp_entry(si->type, offset);
-				return true;
+				return;
 			}
 			if (order)
-				return false;
+				return;
 		}
 
 		spin_lock(&swap_avail_lock);
@@ -1378,7 +1378,6 @@ static bool swap_alloc_slow(swp_entry_t *entry,
 			goto start_over;
 	}
 	spin_unlock(&swap_avail_lock);
-	return false;
 }
 
 /*
-- 
2.34.1

[PATCH 5/5] mm: swap: remove scan_swap_map_slots() references from comments

[Youngjun Park]

The scan_swap_map_slots() helper has been removed, but several comments
still referred to it in swap allocation and reclaim paths. This patch
cleans up those outdated references and reflows the affected comment
blocks to match kernel coding style.

Signed-off-by: Youngjun Park <youngjun.park@lge.com>
---
 mm/swapfile.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 89eb57eee7f7..1dace4356bd1 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -236,11 +236,10 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
 	ret = -nr_pages;
 
 	/*
-	 * When this function is called from scan_swap_map_slots() and it's
-	 * called by vmscan.c at reclaiming folios. So we hold a folio lock
-	 * here. We have to use trylock for avoiding deadlock. This is a special
-	 * case and you should use folio_free_swap() with explicit folio_lock()
-	 * in usual operations.
+	 * We hold a folio lock here. We have to use trylock for
+	 * avoiding deadlock. This is a special case and you should
+	 * use folio_free_swap() with explicit folio_lock() in usual
+	 * operations.
 	 */
 	if (!folio_trylock(folio))
 		goto out;
@@ -1365,14 +1364,13 @@ static void swap_alloc_slow(swp_entry_t *entry,
 		spin_lock(&swap_avail_lock);
 		/*
 		 * if we got here, it's likely that si was almost full before,
-		 * and since scan_swap_map_slots() can drop the si->lock,
 		 * multiple callers probably all tried to get a page from the
 		 * same si and it filled up before we could get one; or, the si
-		 * filled up between us dropping swap_avail_lock and taking
-		 * si->lock. Since we dropped the swap_avail_lock, the
-		 * swap_avail_head list may have been modified; so if next is
-		 * still in the swap_avail_head list then try it, otherwise
-		 * start over if we have not gotten any slots.
+		 * filled up between us dropping swap_avail_lock.
+		 * Since we dropped the swap_avail_lock, the swap_avail_list
+		 * may have been modified; so if next is still in the
+		 * swap_avail_head list then try it, otherwise start over if we
+		 * have not gotten any slots.
 		 */
 		if (plist_node_empty(&si->avail_list))
 			goto start_over;
-- 
2.34.1

Re: [PATCH 1/5] mm, swap: Fix memory leak in setup_clusters() error path

[Kairui Song]

On Wed, Oct 29, 2025 at 8:44 PM Youngjun Park <youngjun.park@lge.com> wrote:
>
> Some error path neglects to free the allocated 'cluster_info',
> causing a memory leak.
>
> Change the error jumps to the 'err_free' label to ensure proper
> cleanup.
>
> Fixes: 07adc4cf1ecd ("mm, swap: implement dynamic allocation of swap table")
> Signed-off-by: Youngjun Park <youngjun.park@lge.com>
> ---
>  mm/swapfile.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index c35bb8593f50..6dc0e7a738bc 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3339,7 +3339,7 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
>          */
>         err = swap_cluster_setup_bad_slot(cluster_info, 0);
>         if (err)
> -               goto err;
> +               goto err_free;
>         for (i = 0; i < swap_header->info.nr_badpages; i++) {
>                 unsigned int page_nr = swap_header->info.badpages[i];
>
> @@ -3347,12 +3347,12 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
>                         continue;
>                 err = swap_cluster_setup_bad_slot(cluster_info, page_nr);
>                 if (err)
> -                       goto err;
> +                       goto err_free;
>         }
>         for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++) {
>                 err = swap_cluster_setup_bad_slot(cluster_info, i);
>                 if (err)
> -                       goto err;
> +                       goto err_free;
>         }
>
>         INIT_LIST_HEAD(&si->free_clusters);
> --
> 2.34.1
>
>

Nice catch.

Maybe it's better to just move free_cluster_info under "err:"? That
might help to avoid more issues like this. free_cluster_info checks if
cluster_info is null already, we just need to initialize *cluster_info
with "= NULL".

Just a nit pick, I'm fine either way.

Reviewed-by: Kairui Song <kasong@tencent.com>

Re: [PATCH 2/5] mm, swap: Use SWP_SOLIDSTATE to determine if swap is rotational

[Kairui Song]

On Wed, Oct 29, 2025 at 05:56:56PM +0800, Youngjun Park wrote:
> The current non rotational check is unreliable
> as the device's rotational status can be changed by a user via sysfs.
> 
> Use the more reliable SWP_SOLIDSTATE flag which is set at swapon time,
> to ensure the nr_rotate_swap count remains consistent.
> Plus, it is easy to read and simple.
> 
> Signed-off-by: Youngjun Park <youngjun.park@lge.com>
> ---
>  mm/swapfile.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 6dc0e7a738bc..b5d42918c01b 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2913,7 +2913,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
>  	if (p->flags & SWP_CONTINUED)
>  		free_swap_count_continuations(p);
>  
> -	if (!p->bdev || !bdev_nonrot(p->bdev))
> +	if (!(p->flags & SWP_SOLIDSTATE))
>  		atomic_dec(&nr_rotate_swap);

Good catch.

Is this introduced by 81a0298bdfab? So we need a Fixes: and backport to stable I think?

>  
>  	mutex_lock(&swapon_mutex);
> -- 
> 2.34.1
> 
> 

Re: [PATCH 4/5] mm: swap: change swap_alloc_slow() to void

[Kairui Song]

On Wed, Oct 29, 2025 at 05:56:58PM +0800, Youngjun Park wrote:
> swap_alloc_slow() does not need to return a bool, as all callers
> handle allocation results via the entry parameter. Update the
> function signature and remove return statements accordingly.
> 
> Signed-off-by: Youngjun Park <youngjun.park@lge.com>
> ---
>  mm/swapfile.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index b5d42918c01b..89eb57eee7f7 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1339,7 +1339,7 @@ static bool swap_alloc_fast(swp_entry_t *entry,
>  }
>  
>  /* Rotate the device and switch to a new cluster */
> -static bool swap_alloc_slow(swp_entry_t *entry,
> +static void swap_alloc_slow(swp_entry_t *entry,
>  			    int order)
>  {
>  	unsigned long offset;
> @@ -1356,10 +1356,10 @@ static bool swap_alloc_slow(swp_entry_t *entry,
>  			put_swap_device(si);
>  			if (offset) {
>  				*entry = swp_entry(si->type, offset);
> -				return true;
> +				return;
>  			}
>  			if (order)
> -				return false;
> +				return;
>  		}
>  
>  		spin_lock(&swap_avail_lock);
> @@ -1378,7 +1378,6 @@ static bool swap_alloc_slow(swp_entry_t *entry,
>  			goto start_over;
>  	}
>  	spin_unlock(&swap_avail_lock);
> -	return false;
>  }
>  

Hi Youngjun,

Thanks for the patch.

I just found a patch from mine series is doing the same thing:
https://lore.kernel.org/linux-mm/20251029-swap-table-p2-v1-15-3d43f3b6ec32@tencent.com/

I'm fine merging your cleanup first, the conflict is really trivial and easy to resolve.

So:

Reviewed-by: Kairui Song <kasong@tencent.com>

>  /*
> -- 
> 2.34.1
> 
> 

Re: [PATCH 1/5] mm, swap: Fix memory leak in setup_clusters() error path

[YoungJun Park]

On Wed, Oct 29, 2025 at 11:41:27PM +0800, Kairui Song wrote:
> On Wed, Oct 29, 2025 at 8:44 PM Youngjun Park <youngjun.park@lge.com> wrote:
> >
> > Some error path neglects to free the allocated 'cluster_info',
> > causing a memory leak.
> >
> > Change the error jumps to the 'err_free' label to ensure proper
> > cleanup.
> >
> > Fixes: 07adc4cf1ecd ("mm, swap: implement dynamic allocation of swap table")
> > Signed-off-by: Youngjun Park <youngjun.park@lge.com>
> > ---
> >  mm/swapfile.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index c35bb8593f50..6dc0e7a738bc 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -3339,7 +3339,7 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
> >          */
> >         err = swap_cluster_setup_bad_slot(cluster_info, 0);
> >         if (err)
> > -               goto err;
> > +               goto err_free;
> >         for (i = 0; i < swap_header->info.nr_badpages; i++) {
> >                 unsigned int page_nr = swap_header->info.badpages[i];
> >
> > @@ -3347,12 +3347,12 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
> >                         continue;
> >                 err = swap_cluster_setup_bad_slot(cluster_info, page_nr);
> >                 if (err)
> > -                       goto err;
> > +                       goto err_free;
> >         }
> >         for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++) {
> >                 err = swap_cluster_setup_bad_slot(cluster_info, i);
> >                 if (err)
> > -                       goto err;
> > +                       goto err_free;
> >         }
> >
> >         INIT_LIST_HEAD(&si->free_clusters);
> > --
> > 2.34.1
> >
> >
> 
> Nice catch.

Hello Kairui.

> Maybe it's better to just move free_cluster_info under "err:"? That
> might help to avoid more issues like this. free_cluster_info checks if
> cluster_info is null already, we just need to initialize *cluster_info
> with "= NULL".

You're right - moving free_cluster_info under 'err:' is cleaner. 
I'll update the code accordingly.

Thanks!
Youngjun Park

> Just a nit pick, I'm fine either way.
> 
> Reviewed-by: Kairui Song <kasong@tencent.com>

Re: [PATCH 2/5] mm, swap: Use SWP_SOLIDSTATE to determine if swap is rotational

[YoungJun Park]

On Thu, Oct 30, 2025 at 12:09:29AM +0800, Kairui Song wrote:
> On Wed, Oct 29, 2025 at 05:56:56PM +0800, Youngjun Park wrote:
> > The current non rotational check is unreliable
> > as the device's rotational status can be changed by a user via sysfs.
> > 
> > Use the more reliable SWP_SOLIDSTATE flag which is set at swapon time,
> > to ensure the nr_rotate_swap count remains consistent.
> > Plus, it is easy to read and simple.
> > 
> > Signed-off-by: Youngjun Park <youngjun.park@lge.com>
> > ---
> >  mm/swapfile.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 6dc0e7a738bc..b5d42918c01b 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -2913,7 +2913,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
> >  	if (p->flags & SWP_CONTINUED)
> >  		free_swap_count_continuations(p);
> >  
> > -	if (!p->bdev || !bdev_nonrot(p->bdev))
> > +	if (!(p->flags & SWP_SOLIDSTATE))
> >  		atomic_dec(&nr_rotate_swap);
> 
> Good catch.
> 
> Is this introduced by 81a0298bdfab? So we need a Fixes: and backport to stable I think?

Okay, I'll add a Fixes tag :)

Thanks,
Youngjun Park

Re: [PATCH 4/5] mm: swap: change swap_alloc_slow() to void

[YoungJun Park]

On Thu, Oct 30, 2025 at 12:13:20AM +0800, Kairui Song wrote:
> On Wed, Oct 29, 2025 at 05:56:58PM +0800, Youngjun Park wrote:
> > swap_alloc_slow() does not need to return a bool, as all callers
> > handle allocation results via the entry parameter. Update the
> > function signature and remove return statements accordingly.
> > 
> > Signed-off-by: Youngjun Park <youngjun.park@lge.com>
> > ---
> >  mm/swapfile.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index b5d42918c01b..89eb57eee7f7 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -1339,7 +1339,7 @@ static bool swap_alloc_fast(swp_entry_t *entry,
> >  }
> >  
> >  /* Rotate the device and switch to a new cluster */
> > -static bool swap_alloc_slow(swp_entry_t *entry,
> > +static void swap_alloc_slow(swp_entry_t *entry,
> >  			    int order)
> >  {
> >  	unsigned long offset;
> > @@ -1356,10 +1356,10 @@ static bool swap_alloc_slow(swp_entry_t *entry,
> >  			put_swap_device(si);
> >  			if (offset) {
> >  				*entry = swp_entry(si->type, offset);
> > -				return true;
> > +				return;
> >  			}
> >  			if (order)
> > -				return false;
> > +				return;
> >  		}
> >  
> >  		spin_lock(&swap_avail_lock);
> > @@ -1378,7 +1378,6 @@ static bool swap_alloc_slow(swp_entry_t *entry,
> >  			goto start_over;
> >  	}
> >  	spin_unlock(&swap_avail_lock);
> > -	return false;
> >  }
> >  
> 
> Hi Youngjun,
> 
> Thanks for the patch.
> 
> I just found a patch from mine series is doing the same thing:
> https://lore.kernel.org/linux-mm/20251029-swap-table-p2-v1-15-3d43f3b6ec32@tencent.com/
> 
> I'm fine merging your cleanup first, the conflict is really trivial and easy to resolve.
> 
> So:
> 
> Reviewed-by: Kairui Song <kasong@tencent.com>
> 
 
Hello Kairui,

Ah, I see you're working on the same area! Thanks for the review and
for being flexible about the merge order. Much appreciated!

Best,
Youngjun Park