linux-kernel - Re: [PATCH 0/3 -v3] GFP

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Message-ID: <20170102154858.GC18048@dhcp22.suse.cz>
Date:   Mon, 2 Jan 2017 16:49:00 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Hillf Danton <hillf.zj@...baba-inc.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3 -v3] GFP_NOFAIL cleanups

On Tue 20-12-16 14:49:01, Michal Hocko wrote:
> Hi,
> This has been posted [1] initially to later be reduced to a single patch
> [2].  Johannes then suggested [3] to split up the second patch and make
> the access to memory reserves by __GF_NOFAIL requests which do not
> invoke the oom killer a separate change. This is patch 3 now.
> 
> Tetsuo has noticed [4] that recent changes have changed GFP_NOFAIL
> semantic for costly order requests. I believe that the primary reason
> why this happened is that our GFP_NOFAIL checks are too scattered
> and it is really easy to forget about adding one. That's why I am
> proposing patch 1 which consolidates all the nofail handling at a single
> place. This should help to make this code better maintainable.
> 
> Patch 2 on top is a further attempt to make GFP_NOFAIL semantic less
> surprising. As things stand currently GFP_NOFAIL overrides the oom killer
> prevention code which is both subtle and not really needed. The patch 2
> has more details about issues this might cause. We have also seen
> a report where __GFP_NOFAIL|GFP_NOFS requests cause the oom killer which
> is premature.
> 
> Patch 3 is an attempt to reduce chances of GFP_NOFAIL requests being
> preempted by other memory consumers by giving them access to memory
> reserves.

a friendly ping on this

> [1] http://lkml.kernel.org/r/20161123064925.9716-1-mhocko@kernel.org
> [2] http://lkml.kernel.org/r/20161214150706.27412-1-mhocko@kernel.org
> [3] http://lkml.kernel.org/r/20161216173151.GA23182@cmpxchg.org
> [4] http://lkml.kernel.org/r/1479387004-5998-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
> 
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-- 
Michal Hocko
SUSE Labs