linux-kernel - Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle PF_LESS

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Date:   Mon, 28 Nov 2016 15:06:51 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Mel Gorman <mgorman@...e.de>, NeilBrown <neilb@...e.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        "dm-devel@...hat.com David Rientjes" <rientjes@...gle.com>,
        Ondrej Kozina <okozina@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Douglas Anderson <dianders@...omium.org>, shli@...nel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle
 PF_LESS_THROTTLE tasks

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