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zsmalloc: account the number of compacted pages correctly

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There exists multiple path may do zram compaction concurrently.
1. auto-compaction triggered during memory reclaim
2. userspace utils write zram<id>/compaction node

So, multiple threads may call zs_shrinker_scan/zs_compact concurrently.
But pages_compacted is a per zsmalloc pool variable and modification
of the variable is not serialized(through under class->lock).
There are two issues here:
1. the pages_compacted may not equal to total number of pages
freed(due to concurrently add).
2. zs_shrinker_scan may not return the correct number of pages
freed(issued by current shrinker).

The fix is simple:
1. account the number of pages freed in zs_compact locally.
2. use actomic variable pages_compacted to accumulate total number.

Link: https://lkml.kernel.org/r/20210202122235.26885-1-wu-yan@tcl.com
Fixes: 860c707dca ("zsmalloc: account the number of compacted pages")
Signed-off-by: Rokudo Yan <wu-yan@tcl.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rokudo Yan 2021-02-25 17:18:31 -08:00 committed by Linus Torvalds
parent f0231305ac
commit 2395928158
3 changed files with 13 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/block/zram/zram_drv.c
View File

@ -1081,7 +1081,7 @@ static ssize_t mm_stat_show(struct device *dev,
zram->limit_pages << PAGE_SHIFT,
max_used << PAGE_SHIFT,
(u64)atomic64_read(&zram->stats.same_pages),
pool_stats.pages_compacted,
atomic_long_read(&pool_stats.pages_compacted),
(u64)atomic64_read(&zram->stats.huge_pages),
(u64)atomic64_read(&zram->stats.huge_pages_since));
up_read(&zram->init_lock);

2
include/linux/zsmalloc.h
View File

@ -35,7 +35,7 @@ enum zs_mapmode {
struct zs_pool_stats {
/* How many pages were migrated (freed) */
unsigned long pages_compacted;
atomic_long_t pages_compacted;
};
struct zs_pool;

17
mm/zsmalloc.c
View File

@ -2212,11 +2212,13 @@ static unsigned long zs_can_compact(struct size_class *class)
return obj_wasted * class->pages_per_zspage;
}
static void __zs_compact(struct zs_pool *pool, struct size_class *class)
static unsigned long __zs_compact(struct zs_pool *pool,
struct size_class *class)
{
struct zs_compact_control cc;
struct zspage *src_zspage;
struct zspage *dst_zspage = NULL;
unsigned long pages_freed = 0;
spin_lock(&class->lock);
while ((src_zspage = isolate_zspage(class, true))) {
@ -2246,7 +2248,7 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
putback_zspage(class, dst_zspage);
if (putback_zspage(class, src_zspage) == ZS_EMPTY) {
free_zspage(pool, class, src_zspage);
pool->stats.pages_compacted += class->pages_per_zspage;
pages_freed += class->pages_per_zspage;
}
spin_unlock(&class->lock);
cond_resched();
@ -2257,12 +2259,15 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
putback_zspage(class, src_zspage);
spin_unlock(&class->lock);
return pages_freed;
}
unsigned long zs_compact(struct zs_pool *pool)
{
int i;
struct size_class *class;
unsigned long pages_freed = 0;
for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
class = pool->size_class[i];
@ -2270,10 +2275,11 @@ unsigned long zs_compact(struct zs_pool *pool)
continue;
if (class->index != i)
continue;
__zs_compact(pool, class);
pages_freed += __zs_compact(pool, class);
}
atomic_long_add(pages_freed, &pool->stats.pages_compacted);
return pool->stats.pages_compacted;
return pages_freed;
}
EXPORT_SYMBOL_GPL(zs_compact);
@ -2290,13 +2296,12 @@ static unsigned long zs_shrinker_scan(struct shrinker *shrinker,
struct zs_pool *pool = container_of(shrinker, struct zs_pool,
shrinker);
pages_freed = pool->stats.pages_compacted;
/*
* Compact classes and calculate compaction delta.
* Can run concurrently with a manually triggered
* (by user) compaction.
*/
pages_freed = zs_compact(pool) - pages_freed;
pages_freed = zs_compact(pool);
return pages_freed ? pages_freed : SHRINK_STOP;
}