[PATCH] mm/shmem: drop the second folio batch from shmem_undo_range()

[PATCH] mm/shmem: drop the second folio batch from shmem_undo_range()

[Qiliang Yuan]

shmem_undo_range() keeps a folio_batch and an array of FOLIO_BATCH_SIZE
indices on its stack. Removing truncated folios from the page cache in
batches added a second folio_batch to collect the folios to delete.

That grows the stack frame by about 200 bytes, past the 1024 byte limit
of mips eyeq6_defconfig built with clang.

Pass fbatch itself to delete_from_page_cache_batch() once the swap
entries are gone, as truncate_inode_pages_range() does. Undoing a failed
fallocate() only removes the folios that are not uptodate, so remove
those one at a time with truncate_inode_folio() as before.

Stack frame of shmem_undo_range() built with clang 18:

  config                before (bytes)  after (bytes)  change
  mips eyeq6_defconfig             928            720    -22%
  x86_64                           920            712    -23%

Fixes: b97fbd541ecba ("mm/shmem: remove truncated folios from the page cache in batches")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202611112032.TMyPU6Rm-lkp@intel.com/
Signed-off-by: Qiliang Yuan <qiliang.yuan@linux.dev>
---
David, this applies on top of b97fbd541ecba in shmem-7.5.misc; please
fold it in if you prefer.
---
 mm/shmem.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 156469423a866..5bcbdd6078a73 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1352,9 +1352,6 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend,
 	index = start;
 	while (index < end && find_lock_entries(mapping, &index, end - 1,
 			&fbatch, indices)) {
-		struct folio_batch remove;
-
-		folio_batch_init(&remove);
 		for (i = 0; i < folio_batch_count(&fbatch); i++) {
 			folio = fbatch.folios[i];
 
@@ -1366,13 +1363,14 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend,
 				continue;
 			}
 
-			if (!unfalloc || !folio_test_uptodate(folio)) {
+			if (!unfalloc)
 				truncate_cleanup_folio(folio);
-				folio_batch_add(&remove, folio);
-			}
+			else if (!folio_test_uptodate(folio))
+				truncate_inode_folio(mapping, folio);
 		}
-		delete_from_page_cache_batch(mapping, &remove);
 		folio_batch_remove_exceptionals(&fbatch);
+		if (!unfalloc)
+			delete_from_page_cache_batch(mapping, &fbatch);
 		for (i = 0; i < folio_batch_count(&fbatch); i++)
 			folio_unlock(fbatch.folios[i]);
 		folio_batch_release(&fbatch);

---
base-commit: b97fbd541ecba5d6640077618e9dfec6f5e71132
change-id: 20261111-bug-mm-shmem-undo-frame-66828e197ad5

Best regards,
-- 
Qiliang Yuan <qiliang.yuan@linux.dev>

Re: [PATCH] mm/shmem: drop the second folio batch from shmem_undo_range()

[Baolin Wang]

On 11/12/26 11:39 AM, Qiliang Yuan wrote:
> shmem_undo_range() keeps a folio_batch and an array of FOLIO_BATCH_SIZE
> indices on its stack. Removing truncated folios from the page cache in
> batches added a second folio_batch to collect the folios to delete.
> 
> That grows the stack frame by about 200 bytes, past the 1024 byte limit
> of mips eyeq6_defconfig built with clang.
> 
> Pass fbatch itself to delete_from_page_cache_batch() once the swap
> entries are gone, as truncate_inode_pages_range() does. Undoing a failed
> fallocate() only removes the folios that are not uptodate, so remove
> those one at a time with truncate_inode_folio() as before.
> 
> Stack frame of shmem_undo_range() built with clang 18:
> 
>    config                before (bytes)  after (bytes)  change
>    mips eyeq6_defconfig             928            720    -22%
>    x86_64                           920            712    -23%
> 
> Fixes: b97fbd541ecba ("mm/shmem: remove truncated folios from the page cache in batches")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202611112032.TMyPU6Rm-lkp@intel.com/
> Signed-off-by: Qiliang Yuan <qiliang.yuan@linux.dev>
> ---
> David, this applies on top of b97fbd541ecba in shmem-7.5.misc; please
> fold it in if you prefer.
> ---

I think you should send out a complete v2, and David could queue your 
new version.

Re: [PATCH] mm/shmem: drop the second folio batch from shmem_undo_range()

[David Hildenbrand (Arm)]

On 11/12/26 09:05, Baolin Wang wrote:
> 
> 
> On 11/12/26 11:39 AM, Qiliang Yuan wrote:
>> shmem_undo_range() keeps a folio_batch and an array of FOLIO_BATCH_SIZE
>> indices on its stack. Removing truncated folios from the page cache in
>> batches added a second folio_batch to collect the folios to delete.
>>
>> That grows the stack frame by about 200 bytes, past the 1024 byte limit
>> of mips eyeq6_defconfig built with clang.
>>
>> Pass fbatch itself to delete_from_page_cache_batch() once the swap
>> entries are gone, as truncate_inode_pages_range() does. Undoing a failed
>> fallocate() only removes the folios that are not uptodate, so remove
>> those one at a time with truncate_inode_folio() as before.
>>
>> Stack frame of shmem_undo_range() built with clang 18:
>>
>>    config                before (bytes)  after (bytes)  change
>>    mips eyeq6_defconfig             928            720    -22%
>>    x86_64                           920            712    -23%
>>
>> Fixes: b97fbd541ecba ("mm/shmem: remove truncated folios from the page cache
>> in batches")
>> Reported-by: kernel test robot <lkp@intel.com>
>> Closes: https://lore.kernel.org/oe-kbuild-all/202611112032.TMyPU6Rm-
>> lkp@intel.com/
>> Signed-off-by: Qiliang Yuan <qiliang.yuan@linux.dev>
>> ---
>> David, this applies on top of b97fbd541ecba in shmem-7.5.misc; please
>> fold it in if you prefer.
>> ---
> 
> I think you should send out a complete v2, and David could queue your new version.

Yes please. I'll drop the old patch from core.git. Should be gone later today.

-- 
Cheers,

David

Re: [PATCH] mm/shmem: drop the second folio batch from shmem_undo_range()

[Qiliang Yuan]

On Thu, Nov 12, 2026 at 09:33:00AM +0100, David Hildenbrand (Arm) wrote:
> On 11/12/26 09:05, Baolin Wang wrote:
>> I think you should send out a complete v2, and David could queue your new version.
>
> Yes please. I'll drop the old patch from core.git. Should be gone later today.

Thanks. This patch is superseded by v3, the complete patch rebuilt from
the v2 in shmem-7.5.misc with this fix folded in. It fixes the stack
frame warning reported at
https://lore.kernel.org/oe-kbuild-all/202611112032.TMyPU6Rm-lkp@intel.com/

v3: https://lore.kernel.org/r/20261112-bug-mm-shmem-undo-batch-v3-1-212db8c24058@linux.dev