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From: Muchun Song <songmuchun@bytedance.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>,
	Shakeel Butt <shakeelb@google.com>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Waiman Long <longman@redhat.com>,
	Linux Memory Management List <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] mm/list_lru: Fix possible race in memcg_reparent_list_lru_node()
Date: Fri, 1 Apr 2022 12:30:19 +0800	[thread overview]
Message-ID: <CAMZfGtUfsGECdA8Nj=_xCurs3LgnB9ATc7J=dFA4_V_Zy-1FnQ@mail.gmail.com> (raw)
In-Reply-To: <20220331181126.815cfe2b05b4281d32b7bf49@linux-foundation.org>

On Fri, Apr 1, 2022 at 9:11 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 31 Mar 2022 09:46:52 +0200 Michal Hocko <mhocko@suse.com> wrote:
>
> > On Thu 31-03-22 06:39:56, Shakeel Butt wrote:
> > > On Wed, Mar 30, 2022 at 07:48:45PM -0700, Roman Gushchin wrote:
> > > >
> > > >
> > > [...]
> > > >
> > > >
> > > > But honestly, I’d drop the original optimization together with
> > > > the fix, if only there is no _real world_ data on the problem and
> > > > the improvement. It seems like it has started as a nice simple
> > > > improvement, but the race makes it complex and probably not worth
> > > > the added complexity and fragility.
> > >
> > > I agree with dropping the original optimization as it is not really
> > > fixing an observed issue which may justify adding some complexity.
> >
> > Completely agreed. The patch as it is proposed is not really acceptable
> > IMHO and I have to say I am worried that this is not the first time we
> > are in a situation when a follow up fixes or unrelated patches are
> > growing in complexity to fit on top of a performance optimizations which
> > do not refer to any actual numbers.
>
> Yup.  I did this:
>
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: mm/list_lru.c: revert "mm/list_lru: optimize memcg_reparent_list_lru_node()"
>
> 405cc51fc1049c73 ("mm/list_lru: optimize memcg_reparent_list_lru_node()")
> has subtle races which are proving ugly to fix.  Revert the original
> optimization.  If quantitative testing indicates that we have a
> significant problem here then other implementations can be looked at.
>
> Fixes: 405cc51fc1049c73 ("mm/list_lru: optimize memcg_reparent_list_lru_node()")
> Cc: Waiman Long <longman@redhat.com>
> Cc: 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>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

  parent reply	other threads:[~2022-04-01  4:31 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-30 17:26 [PATCH v2] mm/list_lru: Fix possible race in memcg_reparent_list_lru_node() Waiman Long
2022-03-30 19:46 ` Roman Gushchin
2022-03-31  2:14 ` Andrew Morton
2022-03-31  2:48   ` Roman Gushchin
2022-03-31  6:39     ` Shakeel Butt
2022-03-31  7:46       ` Michal Hocko
2022-04-01  1:11         ` Andrew Morton
2022-04-01  4:23           ` Shakeel Butt
2022-04-01  4:30           ` Muchun Song [this message]
2022-04-01 11:28           ` Michal Hocko

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