From: Longlong Xia zs_lookup_class_index() lets zram recompression decide whether a newly compressed object would use a smaller size class. It currently classifies the payload size directly, while zs_malloc() adds ZS_HANDLE_SIZE before selecting the class. This makes lookup disagree with allocation near size-class boundaries. With 4 KiB pages, CONFIG_ZSMALLOC_CHAIN_SIZE=8, and 64-bit handles, a 1025-to-1024-byte recompression appears to move from class 64 to class 62 although both allocations use class 64. Conversely, a 1049-to-1025-byte recompression appears to stay in class 64 although the allocations move from class 65 to class 64. As a result, zram can accept replacements with no allocation benefit or reject ones that would save memory, potentially marking the object incompressible. Factor size-class selection into lookup_size_class(), account for the handle there, and use the helper for both lookup and allocation. Fixes: 7c2af309abd2 ("zram: add size class equals check into recompression") Assisted-by: Codex:gpt-5.6-sol Cc: stable@vger.kernel.org Signed-off-by: Longlong Xia --- mm/zsmalloc.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 83f5820c45f9..41b03a9ecec2 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -478,6 +478,11 @@ static int get_size_class_index(int size) return min_t(int, ZS_SIZE_CLASSES - 1, idx); } +static struct size_class *lookup_size_class(struct zs_pool *pool, size_t size) +{ + return pool->size_class[get_size_class_index(size + ZS_HANDLE_SIZE)]; +} + static inline void class_stat_add(struct size_class *class, int type, unsigned long cnt) { @@ -1021,7 +1026,7 @@ unsigned int zs_lookup_class_index(struct zs_pool *pool, unsigned int size) { struct size_class *class; - class = pool->size_class[get_size_class_index(size)]; + class = lookup_size_class(pool, size); return class->index; } @@ -1311,9 +1316,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp, if (!handle) return (unsigned long)ERR_PTR(-ENOMEM); - /* extra space in chunk to keep the handle */ - size += ZS_HANDLE_SIZE; - class = pool->size_class[get_size_class_index(size)]; + class = lookup_size_class(pool, size); /* class->lock effectively protects the zpage migration */ spin_lock(&class->lock); -- 2.43.0