linux-kernel - Re: [PATCH] mm/swap: lru drain on memory reclaim workqueue

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Message-ID: <20160531210116.GA14868@mtj.duckdns.org>
Date:	Tue, 31 May 2016 17:01:16 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Keith Busch <keith.busch@...el.com>
Cc:	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/swap: lru drain on memory reclaim workqueue

On Tue, May 31, 2016 at 02:50:15PM -0600, Keith Busch wrote:
> +	system_mem_wq = alloc_workqueue("events_mem_unbound", WQ_UNBOUND | WQ_MEM_RECLAIM,

So, WQ_MEM_RECLAIM on a shared workqueue doesn't make much sense.
That flag guarantees single concurrency level to the workqueue.  How
would multiple users of a shared workqueue coordinate around that?
What prevents one events_mem_unbound user from depending on, say,
draining lru?  If lru draining requires a rescuer to guarantee forward
progress under memory pressure, that rescuer worker must be dedicated
for that purpose and can't be shared.

Thanks.

-- 
tejun