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

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Date:	Tue, 6 May 2008 07:23:18 +0900
From:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
To:	"Rik van Riel" <riel@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: [-mm][PATCH 4/5] core of reclaim throttle

>  > +     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.

hmmm, AFAIK,
on current kernel, sometimes __GFP_IO task wait for non __GFP_IO task
by lock_page().
Is this wrong?

therefore my patch care only recursive reclaim situation.
I don't object to your opinion. but I hope understand exactly your opinion.

>  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.

Agreed it's easy.
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