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Re: [PATCH 1/2] mm, oom: introduce oom reaper

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On Thu, Dec 17, 2015 at 5:02 AM, Michal Hocko <mhocko@kernel.org> wrote:
> Ups. You are right. I will go with msleep_interruptible(100).

I don't think that's right.

If a signal happens, that loop is now (again) just busy-looping. That
doesn't sound right, although with the maximum limit of 10 attempts,
maybe it's fine - the thing is technically "busylooping", but it will
definitely not busy-loop for very long.

So maybe that code is fine, but I think the signal case might at least
merit a comment?

Also, if you actually do want UNINTERRUPTIBLE (no reaction to signals
at all), but don't want to be seen as being "load" on the system, you
can use TASK_IDLE, which is a combination of TASK_UNINTERRUPTIBLE |
TASK_NOLOAD.

Because if you sleep interruptibly, you do generally need to handle
signals (although that limit count may make it ok in this case).

There's basically three levels:

 - TASK_UNINTERRUPTIBLE: no signal handling at all

 - TASK_KILLABLE: no normal signal handling, but ok to be killed
(needs to check fatal_signal_pending() and exit)

 - TASK_INTERRUPTIBLE: will react to signals

(and then that TASK_IDLE thing that is semantically the same as
uninterruptible, but doesn't count against the load average).

The main use for TASK_KILLABLE is in places where expected semantics
do not allow a EINTR return, but we know that because the process is
about to be killed, we can ignore that, for the simple reason that
nobody will ever *see* the EINTR.

Btw, I think you might want to re-run your test-case after this
change, since the whole "busy loop vs actually sleeping" might just
have changed the result..

              Linus
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Thread

[PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-15 19:40 +0100
  Re: [PATCH 1/2] mm, oom: introduce oom reaper Andrew Morton <akpm@linux-foundation.org> - 2015-12-17 02:00 +0100
    Re: [PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-17 14:10 +0100
      Re: [PATCH 1/2] mm, oom: introduce oom reaper Linus Torvalds <torvalds@linux-foundation.org> - 2015-12-17 21:00 +0100
        Re: [PATCH 1/2] mm, oom: introduce oom reaper Andrew Morton <akpm@linux-foundation.org> - 2015-12-17 21:10 +0100
          Re: [PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-18 13:00 +0100
            Re: [PATCH 1/2] mm, oom: introduce oom reaper Andrew Morton <akpm@linux-foundation.org> - 2015-12-18 22:20 +0100
              Re: [PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-21 09:40 +0100
      Re: [PATCH 1/2] mm, oom: introduce oom reaper Andrew Morton <akpm@linux-foundation.org> - 2015-12-17 22:20 +0100
        Re: [PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-18 13:20 +0100
      Re: [PATCH 1/2] mm, oom: introduce oom reaper Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-12-18 13:20 +0100
        Re: [PATCH 1/2] mm, oom: introduce oom reaper Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-12-20 08:20 +0100
  Re: [PATCH 1/2] mm, oom: introduce oom reaper Andrew Morton <akpm@linux-foundation.org> - 2015-12-18 01:20 +0100
    Re: [PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-18 12:50 +0100
  Re: [PATCH 1/2] mm, oom: introduce oom reaper Paul Gortmaker <paul.gortmaker@windriver.com> - 2015-12-21 21:40 +0100
  Re: [PATCH 1/2] mm, oom: introduce oom reaper Ross Zwisler <zwisler@gmail.com> - 2015-12-24 00:10 +0100
    Re: [PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-24 10:50 +0100
      Re: [PATCH 1/2] mm, oom: introduce oom reaper Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-12-24 12:10 +0100
        Re: [PATCH 1/2] mm, oom: introduce oom reaper Ross Zwisler <zwisler@gmail.com> - 2015-12-24 22:00 +0100
        Re: [PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-25 12:50 +0100
      Re: [PATCH 1/2] mm, oom: introduce oom reaper Ross Zwisler <zwisler@gmail.com> - 2015-12-24 21:50 +0100
        Re: [PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-25 12:40 +0100
          Re: [PATCH 1/2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-25 12:50 +0100

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