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

From: Christoph Lameter
Date: Fri Nov 06 2015 - 07:56:35 EST

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 using outdated vmstat counters.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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