Re: [3.13 regression] kswapd0 and ksoftirqd/0 CPU hogs

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Hi Mikael,

On Tue, May 31, 2016 at 12:06 PM, Mikael Pettersson
<mikpelinux@xxxxxxxxx> wrote:
Finn Thain writes:
 > On Sun, 21 Feb 2016, Mikael Pettersson wrote:
 > > I've done two git bisects on this.  The first one was inconclusive
 > > (pointed to a harmless commit), but the second one ended up with:
 > >
 > > # first bad commit: [ac4de9543aca59f2b763746647577302fbedd57e] Merge branch 'akpm' (patches from Andrew Morton)
 > >
 > > That's a big pile of VM changes, so I think it could be the culprit.
 >
 > I think this issue may date back to v2.6.38 or earlier.
 >
 > The redhat.com bug report was closed in 2012 but Fedora users were still
 > seeing the problem after it was supposedly fixed.
 >   https://bugzilla.redhat.com/show_bug.cgi?id=712019
 >
 > That page also has a link to the bug report for Ubuntu:
 >   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/484045
 >
 > BTW, I came across this recently: "Rik van Riel pointed out that [the
 > kswapd thread] tends to be slow for [the purpose of compaction], and it
 > can get stuck in a shrinker somewhere waiting for a lock."
 >   http://lwn.net/Articles/684611/
 >
 > Perhaps a stack trace would help to ascertain whether this is the same
 > known bug or not (?)
 >
 > --

FWIW, my latest round(s) of bisects identified the following:

fdbadebec27cc92358ed4f593e8763cf10b82687 is the first bad commit
commit fdbadebec27cc92358ed4f593e8763cf10b82687
Author: Li Zefan <lizefan@xxxxxxxxxx>
Date:   Thu Sep 12 15:13:19 2013 -0700

    memcg: remove redundant code in mem_cgroup_force_empty_write()

    vfs guarantees the cgroup won't be destroyed, so it's redundant to get a
    css reference.

    Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
    Acked-by: Michal Hocko <mhocko@xxxxxxx>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
    Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
    Cc: Tejun Heo <tj@xxxxxxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

:040000 040000 1f6b5b056995067c7c60e6f87e9cd1f181e8fbeb ea29d63e70ce2320e144fac7b157a146d41360bf M      mm

This appears to be the first commit in the merge (git bisect refuses to
bisect before it), so either it's it or the problem predates the merge.

That's upstream commit c33bd8354f3a3bb26a98d2b6bf600b7b35657328?

Well done! Looks indeed like a suspect for the behavior you're seeing.
I suppose you will follow up with the mm people?

Thx!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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