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Date: Mon, 24 Apr 2017 15:06:38 +0200
From: Stanislaw Gruszka <sgruszka@redhat.com>
Subject: Re: [PATCH] mm,page_alloc: Split stall warning and failure warning.
Message-ID: <20170424130634.GA6267@redhat.com>
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To: Michal Hocko <mhocko@kernel.org>
Cc: David Rientjes <rientjes@google.com>, Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>, akpm@linux-foundation.org, linux-mm@kvack.org, hannes@cmpxchg.org

On Mon, Apr 24, 2017 at 10:42:17AM +0200, Michal Hocko wrote:
> On Sat 22-04-17 10:10:34, Stanislaw Gruszka wrote:
> [...]
> > > This whole special casing
> > > of debug_guardpage_minorder is just too strange to me. We do have a rate
> > > limit to not flood the log.
> > 
> > I added this check to skip warning if buddy allocator fail, what I
> > considered likely scenario taking the conditions. The check remove
> > warning completely, rate limit only limit the speed warnings shows in
> > logs.
> 
> Yes and this is what I argue against. The feature limits the amount of
> _usable_ memory and as such it changes the behavior of the allocator
> which can lead to all sorts of problems (including high memory pressure,
> stalls, OOM etc.). The warning is there to help debug all those
> problems and removing it just changes that behavior in an unexpected
> way. This is just wrong thing to do IMHO. Even worse so when it
> motivates to make other code in the allocator more complicated.

Allocation problems when using debug_guardpage_minorder should not be
motivation to any mm change. This option is debug only (as name should
suggest already). It purpose is to debug drivers/code that corrupt
memory at random places, it is expected it will cause allocations
problems.

> If there
> is really a problem logs flooded by the allocation failures while using
> the guard page we should address it by a more strict ratelimiting.

Ok, make sense.

Stanislaw

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