Messages in this thread | | | From | Muchun Song <> | Date | Wed, 23 Mar 2022 09:06:03 +0800 | Subject | Re: [PATCH-mm v3] mm/list_lru: Optimize memcg_reparent_list_lru_node() |
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On Wed, Mar 9, 2022 at 10:40 PM Waiman Long <longman@redhat.com> wrote: > > 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.
Hi Waiman,
Sorry for the late reply. Quick question: what if there is an inflight list_lru_add()? How about the following race?
CPU0: CPU1: list_lru_add() spin_lock(&nlru->lock) l = list_lru_from_kmem(memcg) memcg_reparent_objcgs(memcg) memcg_reparent_list_lrus(memcg) memcg_reparent_list_lru() memcg_reparent_list_lru_node() if (!READ_ONCE(nlru->nr_items)) // Miss reparenting return // Assume 0->1 l->nr_items++ // Assume 0->1 nlru->nr_items++
IIUC, we use nlru->lock to serialise this scenario.
Thanks.
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