commit 2395928158059b8f9858365fce7713ce7fef62e4 upstream. 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@xxxxxxx Fixes: 860c707dca155a56 ("zsmalloc: account the number of compacted pages") Signed-off-by: Rokudo Yan <wu-yan@xxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/block/zram/zram_drv.c | 2 +- include/linux/zsmalloc.h | 2 +- mm/zsmalloc.c | 17 +++++++++++------ 3 files changed, 13 insertions(+), 8 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 616ee4f9c233..b243452d4788 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -450,7 +450,7 @@ static ssize_t mm_stat_show(struct device *dev, zram->limit_pages << PAGE_SHIFT, max_used << PAGE_SHIFT, (u64)atomic64_read(&zram->stats.zero_pages), - pool_stats.pages_compacted); + atomic_long_read(&pool_stats.pages_compacted)); up_read(&zram->init_lock); return ret; diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h index 34eb16098a33..05ca2acea8dc 100644 --- a/include/linux/zsmalloc.h +++ b/include/linux/zsmalloc.h @@ -36,7 +36,7 @@ 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; diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index c1ea19478119..8ebcab7b4d2f 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1745,11 +1745,13 @@ 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 page *src_page; struct page *dst_page = NULL; + unsigned long pages_freed = 0; spin_lock(&class->lock); while ((src_page = isolate_source_page(class))) { @@ -1780,7 +1782,7 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class) putback_zspage(pool, class, dst_page); if (putback_zspage(pool, class, src_page) == ZS_EMPTY) - pool->stats.pages_compacted += class->pages_per_zspage; + pages_freed += class->pages_per_zspage; spin_unlock(&class->lock); cond_resched(); spin_lock(&class->lock); @@ -1790,12 +1792,15 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class) putback_zspage(pool, class, src_page); 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]; @@ -1803,10 +1808,11 @@ 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); @@ -1823,13 +1829,12 @@ 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; } -- 2.25.1
