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Date: Mon, 7 Mar 2022 20:39:45 -0800 From: Roman Gushchin <roman.gushchin@...ux.dev> To: Waiman Long <longman@...hat.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Muchun Song <songmuchun@...edance.com> Subject: Re: [PATCH] mm/list_lru: Optimize memcg_drain_list_lru_node() On Mon, Mar 07, 2022 at 10:30:09PM -0500, Waiman Long 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_drain_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. > > Signed-off-by: Waiman Long <longman@...hat.com> Hi Waiman! The patch makes total sense to me, however it needs to be rebased at least on top of "mm: list_lru: rename memcg_drain_all_list_lrus to memcg_reparent_list_lrus". Thanks! > --- > mm/list_lru.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/list_lru.c b/mm/list_lru.c > index 0cd5e89ca063..100ca453e885 100644 > --- a/mm/list_lru.c > +++ b/mm/list_lru.c > @@ -518,6 +518,12 @@ static void memcg_drain_list_lru_node(struct list_lru *lru, int nid, > int dst_idx = dst_memcg->kmemcg_id; > 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. > -- > 2.27.0 > >
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