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Date:   Sat, 12 Sep 2020 10:28:29 +0300
From:   Amir Goldstein <>
To:     Michael Larabel <>
Cc:     Linus Torvalds <>,
        "Ted Ts'o" <>,
        Andreas Dilger <>,
        Ext4 Developers List <>,
        Jan Kara <>,
        linux-fsdevel <>
Subject: Re: Kernel Benchmarking

On Sat, Sep 12, 2020 at 1:40 AM Michael Larabel
<> wrote:
> On 9/11/20 5:07 PM, Linus Torvalds wrote:
> > On Fri, Sep 11, 2020 at 9:19 AM Linus Torvalds
> > <> wrote:
> >> Ok, it's probably simply that fairness is really bad for performance
> >> here in general, and that special case is just that - a special case,
> >> not the main issue.
> > Ahh. It turns out that I should have looked more at the fault path
> > after all. It was higher up in the profile, but I ignored it because I
> > found that lock-unlock-lock pattern lower down.
> >
> > The main contention point is actually filemap_fault(). Your apache
> > test accesses the 'test.html' file that is mmap'ed into memory, and
> > all the threads hammer on that one single file concurrently and that
> > seems to be the main page lock contention.
> >
> > Which is really sad - the page lock there isn't really all that
> > interesting, and the normal "read()" path doesn't even take it. But
> > faulting the page in does so because the page will have a long-term
> > existence in the page tables, and so there's a worry about racing with
> > truncate.
> >
> > Interesting, but also very annoying.
> >
> > Anyway, I don't have a solution for it, but thought I'd let you know
> > that I'm still looking at this.
> >
> >                  Linus
> I've been running your EXT4 patch on more systems and with some
> additional workloads today. While not the original problem, the patch
> does seem to help a fair amount for the MariaDB database sever. This
> wasn't one of the workloads regressing on 5.9 but at least with the
> systems tried so far the patch does make a meaningful improvement to the
> performance. I haven't run into any apparent issues with that patch so
> continuing to try it out on more systems and other database/server
> workloads.


Can you please add a reference to the original problem report and
to the offending commit? This conversation appeared on the list without
this information.

Are filesystems other than ext4 also affected by this performance


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