linux-kernel - Re: [PATCH] mm/list_lru: Optimize memcg_drain_list_lru

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Message-ID: <YifyG3ak3oNOjELK@carbon.dhcp.thefacebook.com>
Date:   Tue, 8 Mar 2022 16:17:31 -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 Tue, Mar 08, 2022 at 10:41:38AM -0500, Waiman Long wrote:
> On 3/7/22 23:39, Roman Gushchin wrote:
> > 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!
> > 
> > 
> This patch was based on the current linux-next tree which includes commit
> ff221bc26bdd ("mm: list_lru: rename memcg_drain_all_list_lrus to
> memcg_reparent_list_lrus"). I do remember to double-check linux-next before
> sending this patch out. In fact, the same patch can be applied to both linux
> and linux-next tree without problem.

I'm looking at the mm tree (https://github.com/hnaz/linux-mm.git) and clearly
see that commit "mm: list_lru: rename memcg_drain_all_list_lrus to
memcg_reparent_list_lrus" eliminated the function with the name
memcg_drain_list_lru_node(), which your patch is touching.
Currently the function is located in list_lru.c and is named
memcg_reparent_list_lru_node().

linux-next is sometimes a bit behind the mm tree.

Thanks!