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| author |   Waiman Long <longman@redhat.com> | 2022-03-22 14:45:44 -0700 |
|---|---|---|
| committer |   Linus Torvalds <torvalds@linux-foundation.org> | 2022-03-22 15:57:08 -0700 |
| commit | 405cc51fc1049c73ae03ce3771a2511a7cf8b240 (patch) | |
| tree | f2a20f0b4f69e2c3ccccdbce390566be79014e3c /mm/list_lru.c | |
| parent | mm: __isolate_lru_page_prepare() in isolate_migratepages_block() (diff) | |
| download | linux-dev-405cc51fc1049c73ae03ce3771a2511a7cf8b240.tar.xz linux-dev-405cc51fc1049c73ae03ce3771a2511a7cf8b240.zip | |
mm/list_lru: optimize memcg_reparent_list_lru_node()
Since commit 2c80cd57c743 ("mm/list_lru.c: fix list_lru_count_node() to
be race free"), we are tracking the total number of lru entries in a
list_lru_node in its nr_items field.
In the case of memcg_reparent_list_lru_node(), there is nothing to be
done if nr_items is 0. We don't even need to take the nlru->lock as no
new lru entry could be added by a racing list_lru_add() to the draining
src_idx memcg at this point.
On systems that serve a lot of containers, it is possible that there can
be thousands of list_lru's present due to the fact that each container
may mount its own container specific filesystems. As a typical
container uses only a few cpus, it is likely that only the list_lru_node
that contains those cpus will be utilized while the rests may be empty.
In other words, there can be a lot of list_lru_node with 0 nr_items.
By skipping a lock/unlock operation and loading a cacheline from
memcg_lrus, a sizeable number of cpu cycles can be saved. That can be
substantial if we are talking about thousands of list_lru_node's with 0
nr_items.
Link: https://lkml.kernel.org/r/20220309144000.1470138-1-longman@redhat.com
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/list_lru.c')
| -rw-r--r-- | mm/list_lru.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/list_lru.c b/mm/list_lru.c index ba76428ceece..c669d87001a6 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -395,6 +395,12 @@ static void memcg_reparent_list_lru_node(struct list_lru *lru, int nid, struct list_lru_one *src, *dst; /* + * If there is no lru entry in this nlru, we can skip it immediately. + */ + if (!READ_ONCE(nlru->nr_items)) + return; + + /* * Since list_lru_{add,del} may be called under an IRQ-safe lock, * we have to use IRQ-safe primitives here to avoid deadlock. */ |