Re: [-mm][PATCH 4/5] core of reclaim throttle

[Rik van Riel]

On Sun, 04 May 2008 22:12:12 +0900
KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:

> +	throttle_on = 1;
> +	current->flags |= PF_RECLAIMING;
> +	wait_event(zone->reclaim_throttle_waitq,
> +		 atomic_add_unless(&zone->nr_reclaimers, 1, MAX_RECLAIM_TASKS));

This is a problem.  Processes without __GFP_FS or __GFP_IO cannot wait on
processes that have those flags set in their gfp_mask, and tasks that do
not have __GFP_IO set cannot wait for tasks with it.  This is because the
tasks that have those flags set may grab locks that the tasks without the
flag are holding, causing a deadlock.

The easiest fix would be to only make tasks with both __GFP_FS and __GFP_IO
sleep.  Tasks that call try_to_free_pages without those flags are relatively
rare and should hopefully not cause any issues.

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