Date: Thu, 2 Apr 2015 08:39:02 +1100
From: Dave Chinner <david@fromorbit.com>
To: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Huang Ying <ying.huang@intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Theodore Ts'o" <tytso@mit.edu>
Subject: Re: [patch 00/12] mm: page_alloc: improve OOM mechanism and policy
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 <20150327150509.GA21119@cmpxchg.org>
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On Wed, Apr 01, 2015 at 05:19:20PM +0200, Michal Hocko wrote:
> On Mon 30-03-15 11:32:40, Dave Chinner wrote:
> > On Fri, Mar 27, 2015 at 11:05:09AM -0400, Johannes Weiner wrote:
> [...]
> > > GFP_NOFS sites are currently one of the sites that can deadlock inside
> > > the allocator, even though many of them seem to have fallback code.
> > > My reasoning here is that if you *have* an exit strategy for failing
> > > allocations that is smarter than hanging, we should probably use that.
> > 
> > We already do that for allocations where we can handle failure in
> > GFP_NOFS conditions. It is, however, somewhat useless if we can't
> > tell the allocator to try really hard if we've already had a failure
> > and we are already in memory reclaim conditions (e.g. a shrinker
> > trying to clean dirty objects so they can be reclaimed).
> > 
> > From that perspective, I think that this patch set aims force us
> > away from handling fallbacks ourselves because a) it makes GFP_NOFS
> > more likely to fail, and b) provides no mechanism to "try harder"
> > when we really need the allocation to succeed.
> 
> You can ask for this "try harder" by __GFP_HIGH flag. Would that help
> in your fallback case?

That dips into GFP_ATOMIC reserves, right? What is the impact on the
GFP_ATOMIC allocations that need it? We typically see network cards
fail GFP_ATOMIC allocations before XFS starts complaining about
allocation failures, so i suspect that this might just make things
worse rather than better...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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