The patch titled
Subject: zsmalloc: account the number of compacted pages correctly
has been added to the -mm tree. Its filename is
zsmalloc-account-the-number-of-compacted-pages-correctly.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/zsmalloc-account-the-number-of-compacted-pages-correctly.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/zsmalloc-account-the-number-of-compacted-pages-correctly.patch
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------------------------------------------------------
From: Rokudo Yan <wu-yan@xxxxxxx>
Subject: zsmalloc: account the number of compacted pages correctly
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>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 2 +-
include/linux/zsmalloc.h | 2 +-
mm/zsmalloc.c | 17 +++++++++++------
3 files changed, 13 insertions(+), 8 deletions(-)
--- a/drivers/block/zram/zram_drv.c~zsmalloc-account-the-number-of-compacted-pages-correctly
+++ a/drivers/block/zram/zram_drv.c
@@ -1082,7 +1082,7 @@ static ssize_t mm_stat_show(struct devic
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);
--- a/include/linux/zsmalloc.h~zsmalloc-account-the-number-of-compacted-pages-correctly
+++ a/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;
--- a/mm/zsmalloc.c~zsmalloc-account-the-number-of-compacted-pages-correctly
+++ a/mm/zsmalloc.c
@@ -2212,11 +2212,13 @@ static unsigned long zs_can_compact(stru
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
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
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
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(st
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;
}
_
Patches currently in -mm which might be from wu-yan@xxxxxxx are
mm-compaction-move-high_pfn-to-the-for-loop-scope.patch
zsmalloc-account-the-number-of-compacted-pages-correctly.patch
