mirrors/linux
2
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-08-31 14:04:27 -04:00
Code Issues Packages Projects Releases Wiki Activity

zsmalloc: account for handle size in class lookup

Browse Source 
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.

Link: https://lore.kernel.org/20260809115518.3791787-1-xialonglong2025@163.com
Fixes: 7c2af309ab ("zram: add size class equals check into recompression")
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Longlong Xia <xialonglong@kylinos.cn>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Longlong Xia
2026-08-09 19:55:18 +08:00
committed by Andrew Morton
parent 1dea8e081e
commit f7bf5cd5b5
1 changed files with 7 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
mm/zsmalloc.c
View File

@@ -552,6 +552,11 @@ 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)
{
@@ -1117,7 +1122,7 @@ 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;
}
@@ -1407,9 +1412,7 @@ 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);