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From:   Alexander Duyck <alexander.duyck@gmail.com>
Date:   Thu, 20 Aug 2020 10:15:17 -0700
Message-ID: <CAKgT0Ueibb_MBvq4CeOO2ZkQfigv5SOC4=13Bfdzdj_9zt4O7Q@mail.gmail.com>
Subject: Re: [RFC PATCH v2 5/5] mm: Split move_pages_to_lru into 3 separate passes
To:     Alex Shi <alex.shi@linux.alibaba.com>
Cc:     Yang Shi <yang.shi@linux.alibaba.com>,
        kbuild test robot <lkp@intel.com>,
        Rong Chen <rong.a.chen@intel.com>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Hugh Dickins <hughd@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        linux-mm <linux-mm@kvack.org>,
        Shakeel Butt <shakeelb@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tejun Heo <tj@kernel.org>, cgroups@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Wei Yang <richard.weiyang@gmail.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
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On Thu, Aug 20, 2020 at 2:58 AM Alex Shi <alex.shi@linux.alibaba.com> wrote=
:
>
>
>
> =E5=9C=A8 2020/8/19 =E4=B8=8B=E5=8D=8810:42, Alexander Duyck =E5=86=99=E9=
=81=93:
> >> It's actually changed the meaning from current func. which I had seen =
a bug if no relock.
> >> but after move to 5.9 kernel, I can not reprodce the bug any more. I a=
m not sure if 5.9 fixed
> >> the problem, and we don't need relock here.
> > So I am not sure what you mean here about "changed the meaning from
> > the current func". Which function are you referring to and what
> > changed?
> >
> > From what I can tell the pages cannot change memcg because they were
> > isolated and had the LRU flag stripped. They shouldn't be able to
> > change destination LRU vector as a result. Assuming that, then they
> > can all be processed under same LRU lock and we can avoid having to
> > release it until we are forced to do so to call putback_lru_page or
> > destroy the compound pages that were freed while we were shrinking the
> > LRU lists.
> >
>
> I had sent a bug which base on 5.8 kernel.
> https://lkml.org/lkml/2020/7/28/465
>
> I am not sure it was fixed in new kernel. The original line was introduce=
d by Hugh Dickins
> I believe it would be great if you can get comments from him.

When I brought this up before you had pointed to the relocking being
due to the fact that the function was reacquiring the lruvec for some
reason. I wonder if the fact that the LRU bit stripping serializing
things made it so that the check for the lruvec after releasing the
lock became redundant.

- Alex