linux-kernel - Re: [RFC PATCH 2/3] mm: Drop use of test_and_set

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Date:   Fri, 14 Aug 2020 14:15:08 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>,
        kbuild test robot <lkp@...el.com>,
        Rong Chen <rong.a.chen@...el.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Hugh Dickins <hughd@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux-mm <linux-mm@...ck.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wei Yang <richard.weiyang@...il.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [RFC PATCH 2/3] mm: Drop use of test_and_set_skip in favor of
 just setting skip

On Fri, Aug 14, 2020 at 7:24 AM Alexander Duyck
<alexander.duyck@...il.com> wrote:
>
> On Fri, Aug 14, 2020 at 12:19 AM Alex Shi <alex.shi@...ux.alibaba.com> wrote:
> >
> >
> >
> > 在 2020/8/13 下午12:02, Alexander Duyck 写道:
> > >
> > > Since we have dropped the late abort case we can drop the code that was
> > > clearing the LRU flag and calling page_put since the abort case will now
> > > not be holding a reference to a page.
> > >
> > > Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> >
> > seems the case-lru-file-mmap-read case drop about 3% on this patch in a rough testing.
> > on my 80 core machine.
>
> I'm not sure how it could have that much impact on the performance
> since the total effect would just be dropping what should be a
> redundant test since we tested the skip bit before we took the LRU
> bit, so we shouldn't need to test it again after.
>
> I finally got my test setup working last night. I'll have to do some
> testing in my environment and I can start trying to see what is going
> on.

So I ran the case-lru-file-mmap-read a few times and I don't see how
it is supposed to be testing the compaction code. It doesn't seem like
compaction is running at least on my system as a result of the test
script. I wonder if testing this code wouldn't be better done using
something like thpscale from the
mmtests(https://github.com/gormanm/mmtests)? It seems past changes to
the compaction code were tested using that, and the config script for
the test explains that it is designed specifically to stress the
compaction code. I have the test up and running now and hope to
collect results over the weekend.

There is one change I will probably make to this patch and that is to
place the new code that is setting skip_updated where the old code was
calling test_and_set_skip_bit. By doing that we can avoid extra checks
and it should help to reduce possible collisions when setting the skip
bit in the pageblock flags.

Thanks.

- Alex