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Date: Mon, 28 Nov 2016 15:06:51 +0100
From: Michal Hocko <mhocko@kernel.org>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>, NeilBrown <neilb@suse.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        "dm-devel@redhat.com David Rientjes" <rientjes@google.com>,
        Ondrej Kozina <okozina@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Douglas Anderson <dianders@chromium.org>, shli@kernel.org,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>
Subject: Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle
 PF_LESS_THROTTLE tasks
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On Thu 24-11-16 12:10:08, Mikulas Patocka wrote:
> 
> 
> On Thu, 24 Nov 2016, Michal Hocko wrote:
[...]
> > Please note that even
> > GFP_NOWAIT allocations will wake up kspwad which should clean up that
> 
> The mempool is also using GFP_NOIO allocations - so do you claim that it 
> should not use GFP_NOIO too?

No, I am not claiming that. The last time I have asked the throttling
didn't seem to serious enough to cause any problems. If the memory
reclaim throttling is serious enough then let's measure and evaluate it.

> You should provide a clear API that the block device drivers should use to 
> allocate memory - not to apply band aid to vm throttling problems as they 
> are being discovered.

This is easier said than done, I am afraid. We have been using GFP_NOIO
in mempool for years and there were no major complains.
-- 
Michal Hocko
SUSE Labs