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Re: [PATCH v2 3/3] percpu: improve allocation success rate for non-GFP_KERNEL callers

From Tahsin Erdogan <tahsin@google.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2 3/3] percpu: improve allocation success rate for non-GFP_KERNEL callers
Date 2017-02-27 18:10 +0100
Message-ID <tfwYa-b8-15@gated-at.bofh.it> (permalink)
References <teVce-7pj-3@gated-at.bofh.it> <teYWt-1zx-1@gated-at.bofh.it> <tfqzo-491-15@gated-at.bofh.it> <tftdU-5Yo-25@gated-at.bofh.it> <tfvpn-7rK-5@gated-at.bofh.it>
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On Mon, Feb 27, 2017 at 7:25 AM, Michal Hocko <mhocko@kernel.org> wrote:
>         /*
>          * No space left.  Create a new chunk.  We don't want multiple
>          * tasks to create chunks simultaneously.  Serialize and create iff
>          * there's still no empty chunk after grabbing the mutex.
>          */
>         if (is_atomic)
>                 goto fail;
>
> right before pcpu_populate_chunk so is this actually a problem?

Yes, this prevents adding more pcpu chunks and so cause "atomic" allocations
to fail more easily.

>> By the way, I now noticed the might_sleep() in alloc_vmap_area() which makes
>> it unsafe to call vmalloc* in GFP_ATOMIC contexts. It was added recently:
>
> Do we call alloc_vmap_area from true atomic contexts (aka from under
> spinlocks etc)? I thought this was a nogo and GFP_NOWAIT resp.
> GFP_ATOMIC was more about optimistic request resp. access to memory
> reserves rather than true atomicity requirements.

In the call path that I am trying to fix, the caller uses GFP_NOWAIT mask.
The caller is holding a spinlock (request_queue->queue_lock) so we can't afford
to sleep.

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[PATCH 3/3] percpu: improve allocation success rate for non-GFP_KERNEL callers Tahsin Erdogan <tahsin@google.com> - 2017-02-25 22:10 +0100
  Re: [PATCH 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers kbuild test robot <lkp@intel.com> - 2017-02-26 01:00 +0100
  Re: [PATCH 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers kbuild test robot <lkp@intel.com> - 2017-02-26 01:50 +0100
    [PATCH v2 3/3] percpu: improve allocation success rate for non-GFP_KERNEL callers Tahsin Erdogan <tahsin@google.com> - 2017-02-26 05:50 +0100
      Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Michal Hocko <mhocko@kernel.org> - 2017-02-27 11:20 +0100
        Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tahsin Erdogan <tahsin@google.com> - 2017-02-27 14:10 +0100
          Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Michal Hocko <mhocko@kernel.org> - 2017-02-27 16:30 +0100
            Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Michal Hocko <mhocko@kernel.org> - 2017-02-27 18:10 +0100
              Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Michal Hocko <mhocko@kernel.org> - 2017-02-27 18:40 +0100
                Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tahsin Erdogan <tahsin@google.com> - 2017-02-27 20:40 +0100
                Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Michal Hocko <mhocko@kernel.org> - 2017-02-27 20:50 +0100
            Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tahsin Erdogan <tahsin@google.com> - 2017-02-27 18:10 +0100
          Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tahsin Erdogan <tahsin@google.com> - 2017-02-27 21:30 +0100
            Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tejun Heo <tj@kernel.org> - 2017-02-27 21:40 +0100
              Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tahsin Erdogan <tahsin@google.com> - 2017-02-27 21:50 +0100
                Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tahsin Erdogan <tahsin@google.com> - 2017-02-27 22:20 +0100
                Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tejun Heo <tj@kernel.org> - 2017-02-27 22:40 +0100
                Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tejun Heo <tj@kernel.org> - 2017-02-27 23:40 +0100
          Re: [PATCH v2 3/3] percpu: improve allocation success rate for  non-GFP_KERNEL callers Tejun Heo <tj@kernel.org> - 2017-02-27 23:40 +0100

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