linux-kernel - Re: [RFC][PATCH] lru_add_drain_all() don't use schedule_on_each

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Date:	Fri, 24 Oct 2008 06:55:47 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Lee Schermerhorn <lee.schermerhorn@...com>, linux-mm@...ck.org,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [RFC][PATCH] lru_add_drain_all() don't use schedule_on_each_cpu()

On Fri, Oct 24, 2008 at 01:54:46PM +0900, KOSAKI Motohiro wrote:
> > > 
> > > Actually, schedule_on_each_cpu() is very problematic function.
> > > it introduce the dependency of all worker on keventd_wq, 
> > > but we can't know what lock held by worker in kevend_wq because
> > > keventd_wq is widely used out of kernel drivers too.
> > > 
> > > So, the task of any lock held shouldn't wait on keventd_wq.
> > > Its task should use own special purpose work queue.
> > 
> > I don't see a better way to solve it, other than avoiding lru_add_drain_all
> 
> Well,
> 
> Unfortunately, lru_add_drain_all is also used some other VM place
> (page migration and memory hotplug).
> and page migration's usage is the same of this mlock usage.
> (1. grab mmap_sem  2.  call lru_add_drain_all)
> 
> Then, change mlock usage isn't solution ;-)

No, not mlock alone.
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