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authorWaiman Long <longman@redhat.com>2022-03-22 14:45:44 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-22 15:57:08 -0700
commit405cc51fc1049c73ae03ce3771a2511a7cf8b240 (patch)
treef2a20f0b4f69e2c3ccccdbce390566be79014e3c /mm/list_lru.c
parent89f6c88a6ab4a11deb14c270f7f1454cda4f73d6 (diff)
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.c6
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.
*/