linux-kernel - Re: [patch 3/3] vmstat: Create our own workqueue

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Date:	Fri, 6 Nov 2015 06:56:28 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
cc:	htejun@...il.com, akpm@...ux-foundation.org, mhocko@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, hannes@...xchg.org, mgorman@...e.de
Subject: Re: [patch 3/3] vmstat: Create our own workqueue

On Fri, 6 Nov 2015, Tetsuo Handa wrote:

> So, if you refer to the blocking of the execution of vmstat updates,
> description for patch 3/3 sould be updated to something like below?

Ok that is much better.

> ----------
> Since __GFP_WAIT memory allocations do not call schedule()
> when there is nothing to reclaim, and workqueue does not kick
> remaining workqueue items unless in-flight workqueue item calls
> schedule(), __GFP_WAIT memory allocation requests by workqueue
> items can block vmstat_update work item forever.
>
> Since zone_reclaimable() decision depends on vmstat counters
> to be up to dated, a silent lockup occurs because a workqueue
> item doing a __GFP_WAIT memory allocation request continues
> using outdated vmstat counters.
>
> In order to fix this problem, we need to allocate a dedicated
> workqueue for vmstat. Note that this patch itself does not fix
> lockup problem. Tejun will develop a patch which detects lockup
> situation and kick remaining workqueue items.
> ----------
>
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