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

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Date:	Fri, 22 Jul 2016 19:04:25 +1000
From:	NeilBrown <neilb@...e.com>
To:	Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org
Cc:	Mikulas Patocka <mpatocka@...hat.com>,
	Ondrej Kozina <okozina@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, dm-devel@...hat.com,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [RFC PATCH 2/2] mm, mempool: do not throttle PF_LESS_THROTTLE tasks

On Fri, Jul 22 2016, NeilBrown wrote:

>
> Looking at the current code, __GFP_DIRECT_RECLAIM is disabled the first
> time through, but if the pool is empty, direct-reclaim is allowed on the
> next attempt.  Presumably this is where the throttling comes in ??  I
> suspect that it really shouldn't do that. It should leave kswapd to do
> reclaim (so __GFP_KSWAPD_RECLAIM is appropriate) and only wait in
> mempool_alloc where pool->wait can wake it up.

Actually, thinking about the kswapd connection, it might make sense
for mempool_alloc() to wait in the relevant pgdata->pfmemalloc_wait as
well as waiting on pool->wait.  What way it should be able to proceed as
soon as any memory is available.  I don't know what the correct 'pgdata'
is though.

Just a thought,
NeilBrown

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