linux-kernel - Re: [PATCH] vmscan: do not throttle kthreads due to too_many

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Message-ID: <5655D789.80201@suse.cz>
Date:	Wed, 25 Nov 2015 16:45:13 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vmscan: do not throttle kthreads due to too_many_isolated

On 11/25/2015 04:36 PM, Vladimir Davydov wrote:
> Block device drivers often hand off io request processing to kernel
> threads (example: device mapper). If such a thread calls kmalloc, it can
> dive into direct reclaim path and end up waiting for too_many_isolated
> to return false, blocking writeback. This can lead to a dead lock if the

Shouldn't such allocation lack __GFP_IO to prevent this and other kinds of
deadlocks? And/or have mempools? PF_KTHREAD looks like a big hammer to me that
will solve only one potential problem...

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