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

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Message-Id: <20161220134904.21023-1-mhocko@kernel.org>
Date:   Tue, 20 Dec 2016 14:49:01 +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: [PATCH 0/3 -v3] GFP_NOFAIL cleanups

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.

[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