[PATCH v3] mm/slub: free prefilled empty sheaves consistently

[hu.shengming]

From: Shengming Hu <hu.shengming@xxxxxxxxxx>

Empty sheaves allocated by alloc_empty_sheaf() should be released with
free_empty_sheaf().

Move the empty-sheaf capacity initialization into __alloc_empty_sheaf()
and use it for oversized prefilled sheaves as well.

This keeps the prefill paths consistent: after flushing an oversized or
pfmemalloc sheaf, release the now-empty sheaf through free_empty_sheaf()
instead of kfree().

Signed-off-by: Shengming Hu <hu.shengming@xxxxxxxxxx>
---
Changes in v2:
- Rework the change as suggested by Harry.
- Teach __alloc_empty_sheaf() to initialize capacity and pfmemalloc.
- Allocate oversized prefilled sheaves through __alloc_empty_sheaf().
- Free flushed oversized and pfmemalloc sheaves through free_empty_sheaf().
- Link to v1: https://lore.kernel.org/all/20260521195015105Y4zvKHj0TfPZEujixy9Vo@xxxxxxxxxx/

Changes in v3:
- Address Hao's comments:
- Drop the redundant `pfmemalloc` initialization in
  __alloc_empty_sheaf().
- Keep initializing `capacity` and `pfmemalloc` in the normal-sized
  prefill path, since the sheaf may be reused rather than freshly
  allocated.
- Link to v2: https://lore.kernel.org/all/20260522145900248m-nBcy07_SCDk2ATDWfmg@xxxxxxxxxx/

---
 mm/slub.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 04692a6f9128..f4c06bf43f2d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2782,6 +2782,7 @@ static struct slab_sheaf *__alloc_empty_sheaf(struct kmem_cache *s, gfp_t gfp,
 		return NULL;

 	sheaf->cache = s;
+	sheaf->capacity = capacity;

 	stat(s, SHEAF_ALLOC);

@@ -5015,21 +5016,15 @@ kmem_cache_prefill_sheaf(struct kmem_cache *s, gfp_t gfp, unsigned int size)

 	if (unlikely(size > s->sheaf_capacity)) {

-		sheaf = kzalloc_flex(*sheaf, objects, size, gfp);
+		sheaf = __alloc_empty_sheaf(s, gfp, size);
 		if (!sheaf)
 			return NULL;

 		stat(s, SHEAF_PREFILL_OVERSIZE);
-		sheaf->cache = s;
-		sheaf->capacity = size;

-		/*
-		 * we do not need to care about pfmemalloc here because oversize
-		 * sheaves area always flushed and freed when returned
-		 */
 		if (!__kmem_cache_alloc_bulk(s, gfp, size,
 					     &sheaf->objects[0])) {
-			kfree(sheaf);
+			free_empty_sheaf(s, sheaf);
 			return NULL;
 		}

@@ -5097,7 +5092,7 @@ void kmem_cache_return_sheaf(struct kmem_cache *s, gfp_t gfp,
 	if (unlikely((sheaf->capacity != s->sheaf_capacity)
 		     || sheaf->pfmemalloc)) {
 		sheaf_flush_unused(s, sheaf);
-		kfree(sheaf);
+		free_empty_sheaf(s, sheaf);
 		return;
 	}

-- 
2.25.1