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From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 7 Sep 2021 11:19:26 -0700
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Subject: Re: [memcg] 0f12156dff: will-it-scale.per_process_ops -33.6% regression
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Minchan Kim <minchan@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        kernel test robot <oliver.sang@intel.com>,
        Vasily Averin <vvs@virtuozzo.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrei Vagin <avagin@gmail.com>,
        Borislav Petkov <bp@alien8.de>, Borislav Petkov <bp@suse.de>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Jeff Layton <jlayton@kernel.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
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        "Huang, Ying" <ying.huang@intel.com>,
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On Tue, Sep 7, 2021 at 10:54 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Tue, Sep 7, 2021 at 9:49 AM Shakeel Butt <shakeelb@google.com> wrote:
> >
> > On Tue, Sep 7, 2021 at 9:40 AM Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> > >
> > > We are worried about them. I'm considering reverting several of them
> > > because I think the problems are
> > >
> > >  (a) big
> > >
> > >  (b) nontrivial
> > >
> > > and the patches clearly weren't ready and people weren't aware of this issue.
> >
> > Sounds good to me. Please let me know which patches you are planning
> > to revert. I will work on the followup to make those acceptable.
>
> The one that looks clear-cut is the one in this thread:
>
>     0f12156dff28 memcg: enable accounting for file lock caches
>
> which seems to result in regressions on multiple machines and just be
> very bad for anything that uses file locking. I'm not entirely sure
> how much that would show up in real life, but I can most definitely
> imagine it being a problem on a real load.
>
> There's a few other regression reports I've seen, like
>
>     5387c90490f7 mm/memcg: improve refill_obj_stock() performance
>
> but that one had mixed reports (it improved another benchmark), and it
> looks like Minchan has a fix for the regression already.
>
> And
>
>     aa48e47e3906 memcg: infrastructure to flush memcg stats
>     b65584344415 memcg: enable accounting for pollfd and select bits arrays
>
> were reported as a regression in -mm, but not in mainline yet.
>
> I assume (but didn't check) that aa48e47e3906 is a bigger deal to revert.
>

I am suspecting aa48e47e3906 might be similar to [1]. I am testing that theory.

[1] https://lore.kernel.org/all/20210811031734.GA5193@xsang-OptiPlex-9020/T/#u