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Subject[v7 PATCH 10/12] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers
Date
Now nr_deferred is available on per memcg level for memcg aware shrinkers, so don't need
allocate shrinker->nr_deferred for such shrinkers anymore.

The prealloc_memcg_shrinker() would return -ENOSYS if !CONFIG_MEMCG or memcg is disabled
by kernel command line, then shrinker's SHRINKER_MEMCG_AWARE flag would be cleared.
This makes the implementation of this patch simpler.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
mm/vmscan.c | 33 ++++++++++++++++++---------------
1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 748aa6e90f83..dfde6e7fd7f5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -338,6 +338,9 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
{
int id, ret = -ENOMEM;

+ if (mem_cgroup_disabled())
+ return -ENOSYS;
+
down_write(&shrinker_rwsem);
/* This may call shrinker, so it must use down_read_trylock() */
id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
@@ -417,7 +420,7 @@ static bool writeback_throttling_sane(struct scan_control *sc)
#else
static int prealloc_memcg_shrinker(struct shrinker *shrinker)
{
- return 0;
+ return -ENOSYS;
}

static void unregister_memcg_shrinker(struct shrinker *shrinker)
@@ -528,8 +531,18 @@ unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone
*/
int prealloc_shrinker(struct shrinker *shrinker)
{
- unsigned int size = sizeof(*shrinker->nr_deferred);
+ unsigned int size;
+ int err;

+ if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
+ err = prealloc_memcg_shrinker(shrinker);
+ if (err != -ENOSYS)
+ return err;
+
+ shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
+ }
+
+ size = sizeof(*shrinker->nr_deferred);
if (shrinker->flags & SHRINKER_NUMA_AWARE)
size *= nr_node_ids;

@@ -537,26 +550,16 @@ int prealloc_shrinker(struct shrinker *shrinker)
if (!shrinker->nr_deferred)
return -ENOMEM;

- if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
- if (prealloc_memcg_shrinker(shrinker))
- goto free_deferred;
- }

return 0;
-
-free_deferred:
- kfree(shrinker->nr_deferred);
- shrinker->nr_deferred = NULL;
- return -ENOMEM;
}

void free_prealloced_shrinker(struct shrinker *shrinker)
{
- if (!shrinker->nr_deferred)
- return;
-
- if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+ if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
unregister_memcg_shrinker(shrinker);
+ return;
+ }

kfree(shrinker->nr_deferred);
shrinker->nr_deferred = NULL;
--
2.26.2
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