zsmalloc: account the number of compacted pages correctly

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@tcl.com
Fixes: 860c707dca155a56 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 1b69720..7111684 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1078,7 +1078,7 @@ 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));
        up_read(&zram->init_lock);
 

diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
index 4807ca4..2a430e7 100644 (file)
--- a/include/linux/zsmalloc.h
+++ b/include/linux/zsmalloc.h
@@ -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;

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index cdfaaad..7a0b79b 100644 (file)
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -2216,11 +2216,13 @@ 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))) {
@@ -2250,7 +2252,7 @@ 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();
@@ -2261,12 +2263,15 @@ 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];
@@ -2274,10 +2279,11 @@ 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);
 
@@ -2294,13 +2300,12 @@ 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;
 }