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Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically

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On 12/01/2016 04:25 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> __alloc_pages_may_oom makes sure to skip the OOM killer depending on
> the allocation request. This includes lowmem requests, costly high
> order requests and others. For a long time __GFP_NOFAIL acted as an
> override for all those rules. This is not documented and it can be quite
> surprising as well. E.g. GFP_NOFS requests are not invoking the OOM
> killer but GFP_NOFS|__GFP_NOFAIL does so if we try to convert some of
> the existing open coded loops around allocator to nofail request (and we
> have done that in the past) then such a change would have a non trivial
> side effect which is not obvious. Note that the primary motivation for
> skipping the OOM killer is to prevent from pre-mature invocation.
>
> The exception has been added by 82553a937f12 ("oom: invoke oom killer
> for __GFP_NOFAIL"). The changelog points out that the oom killer has to
> be invoked otherwise the request would be looping for ever. But this
> argument is rather weak because the OOM killer doesn't really guarantee
> any forward progress for those exceptional cases - e.g. it will hardly
> help to form costly order - I believe we certainly do not want to kill
> all processes and eventually panic the system just because there is a
> nasty driver asking for order-9 page with GFP_NOFAIL not realizing all
> the consequences - it is much better this request would loop for ever
> than the massive system disruption, lowmem is also highly unlikely to be
> freed during OOM killer and GFP_NOFS request could trigger while there
> is still a lot of memory pinned by filesystems.
>
> This patch simply removes the __GFP_NOFAIL special case in order to have
> a more clear semantic without surprising side effects. Instead we do
> allow nofail requests to access memory reserves to move forward in both
> cases when the OOM killer is invoked and when it should be supressed.
> __alloc_pages_nowmark helper has been introduced for that purpose.
>
> Signed-off-by: Michal Hocko <mhocko@suse.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

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[PATCH 0/2] GFP_NOFAIL cleanups Michal Hocko <mhocko@kernel.org> - 2016-12-01 16:30 +0100
  [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically Michal Hocko <mhocko@kernel.org> - 2016-12-01 16:30 +0100
    Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Vlastimil Babka <vbabka@suse.cz> - 2016-12-02 08:30 +0100
    Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-12-05 14:50 +0100
      Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Michal Hocko <mhocko@kernel.org> - 2016-12-05 15:20 +0100
        Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Michal Hocko <mhocko@kernel.org> - 2016-12-06 09:50 +0100
        Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-12-06 11:40 +0100
          Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Vlastimil Babka <vbabka@suse.cz> - 2016-12-06 12:10 +0100
            Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Michal Hocko <mhocko@kernel.org> - 2016-12-06 20:30 +0100
          Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Michal Hocko <mhocko@kernel.org> - 2016-12-06 20:30 +0100
            Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2016-12-08 14:00 +0100
              Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL  automatically Michal Hocko <mhocko@kernel.org> - 2016-12-08 14:50 +0100
  [PATCH 1/2] mm: consolidate GFP_NOFAIL checks in the allocator slowpath Michal Hocko <mhocko@kernel.org> - 2016-12-01 16:30 +0100

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