Re: mm allocation failure and hang when running xfstests generic/269 on xfs

From	Brian Foster <bfoster@redhat.com>
Newsgroups	linux.kernel
Subject	Re: mm allocation failure and hang when running xfstests generic/269 on xfs
Date	2017-03-02 16:00 +0100
Message-ID	<tgAn0-3FV-5@gated-at.bofh.it> (permalink)
References	(5 earlier) <tgyEx-2Jl-1@gated-at.bofh.it> <tgzqV-2ZE-11@gated-at.bofh.it> <tgzqW-2ZE-25@gated-at.bofh.it> <tgzqW-2ZE-27@gated-at.bofh.it> <tgzqW-2ZE-23@gated-at.bofh.it>
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On Thu, Mar 02, 2017 at 02:50:01PM +0100, Michal Hocko wrote:
> On Thu 02-03-17 08:41:58, Brian Foster wrote:
> > On Thu, Mar 02, 2017 at 02:27:55PM +0100, Michal Hocko wrote:
> [...]
> > > I see your argument about being in sync with other kmem helpers but
> > > those are bit different because regular page/slab allocators allow never
> > > fail semantic (even though this is mostly ignored by those helpers which
> > > implement their own retries but that is a different topic).
> > > 
> > 
> > ... but what I'm trying to understand here is whether this failure
> > scenario is specific to vmalloc() or whether the other kmem_*()
> > functions are susceptible to the same problem. For example, suppose we
> > replaced this kmem_zalloc_greedy() call with a kmem_zalloc(PAGE_SIZE,
> > KM_SLEEP) call. Could we hit the same problem if the process is killed?
> 
> Well, kmem_zalloc uses kmalloc which can also fail when we are out of
> memory but in that case we can expect the OOM killer releasing some
> memory which would allow us to make a forward progress on the next
> retry. So essentially retrying around kmalloc is much more safe in this
> regard. Failing vmalloc might be permanent because there is no vmalloc
> space to allocate from or much more likely due to already mentioned
> patch. So vmalloc is different, really.

Right.. that's why I'm asking. So it's technically possible but highly
unlikely due to the different failure characteristics. That seems
reasonable to me, then. 

To be clear, do we understand what causes the vzalloc() failure to be
effectively permanent in this specific reproducer? I know you mention
above that we could be out of vmalloc space, but that doesn't clarify
whether there are other potential failure paths or then what this has to
do with the fact that the process was killed. Does the pending signal
cause the subsequent failures or are you saying that there is some other
root cause of the failure, this process would effectively be spinning
here anyways, and we're just noticing it because it's trying to exit?

Brian

> -- 
> Michal Hocko
> SUSE Labs
> 
> --
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Thread

Re: mm allocation failure and hang when running xfstests generic/269  on xfs Christoph Hellwig <hch@infradead.org> - 2017-03-02 01:40 +0100
  Re: mm allocation failure and hang when running xfstests generic/269  on xfs Xiong Zhou <xzhou@redhat.com> - 2017-03-02 06:40 +0100
    Re: mm allocation failure and hang when running xfstests generic/269  on xfs Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-03-02 07:50 +0100
      Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 09:50 +0100
        Re: mm allocation failure and hang when running xfstests generic/269  on xfs Xiong Zhou <xzhou@redhat.com> - 2017-03-02 10:30 +0100
    Re: mm allocation failure and hang when running xfstests generic/269  on xfs Bob Liu <liubo95@huawei.com> - 2017-03-02 07:50 +0100
    Re: mm allocation failure and hang when running xfstests generic/269on xfs Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-03-02 12:50 +0100
    Re: mm allocation failure and hang when running xfstests generic/269  on xfs Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-03-02 13:00 +0100
      Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 13:30 +0100
        Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 13:30 +0100
          Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 14:10 +0100
            Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 15:00 +0100
              Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 15:00 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 16:00 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 16:40 +0100
                [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Michal Hocko <mhocko@kernel.org> - 2017-03-02 16:50 +0100
                [PATCH 2/2] xfs: back off from kmem_zalloc_greedy if the task is killed Michal Hocko <mhocko@kernel.org> - 2017-03-02 16:50 +0100
                Re: [PATCH 2/2] xfs: back off from kmem_zalloc_greedy if the task         is killed Christoph Hellwig <hch@lst.de> - 2017-03-02 17:00 +0100
                Re: [PATCH 2/2] xfs: back off from kmem_zalloc_greedy if the task is  killed Brian Foster <bfoster@redhat.com> - 2017-03-02 17:10 +0100
                Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Brian Foster <bfoster@redhat.com> - 2017-03-02 17:10 +0100
                Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Christoph Hellwig <hch@lst.de> - 2017-03-02 17:20 +0100
                Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Michal Hocko <mhocko@kernel.org> - 2017-03-02 17:40 +0100
                Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-03-02 17:50 +0100
                Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Dave Chinner <david@fromorbit.com> - 2017-03-04 00:00 +0100
                Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-03-04 00:30 +0100
                Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Dave Chinner <david@fromorbit.com> - 2017-03-04 05:50 +0100
                Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail Michal Hocko <mhocko@kernel.org> - 2017-03-06 14:30 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 20:20 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Christoph Hellwig <hch@infradead.org> - 2017-03-02 19:00 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 20:20 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 16:00 +0100
                Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 18:40 +0100
              Re: mm allocation failure and hang when running xfstests generic/269  on xfs Brian Foster <bfoster@redhat.com> - 2017-03-02 15:00 +0100
              Re: mm allocation failure and hang when running xfstests generic/269  on xfs Michal Hocko <mhocko@kernel.org> - 2017-03-02 15:10 +0100
              Re: mm allocation failure and hang when running xfstests generic/269 on xfs Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-03-02 17:00 +0100

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