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Date:   Fri, 14 Aug 2020 14:15:08 -0700
From:   Alexander Duyck <>
To:     Alex Shi <>
Cc:     Yang Shi <>,
        kbuild test robot <>,
        Rong Chen <>,
        Konstantin Khlebnikov <>,
        "Kirill A. Shutemov" <>,
        Hugh Dickins <>,
        LKML <>,
        Daniel Jordan <>,
        linux-mm <>,
        Shakeel Butt <>,
        Matthew Wilcox <>,
        Johannes Weiner <>,
        Tejun Heo <>,,
        Andrew Morton <>,
        Wei Yang <>,
        Mel Gorman <>,
        Joonsoo Kim <>
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
<> wrote:
> On Fri, Aug 14, 2020 at 12:19 AM Alex Shi <> 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 <>
> >
> > 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( 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.


- Alex

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