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

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Message-Id: <20081027193918.9667.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Mon, 27 Oct 2008 19:42:40 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Nick Piggin <npiggin@...e.de>, 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>,
	Gautham Shenoy <ego@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	Rusty Russell <rusty@...tcorp.com.au>, mpm <mpm@...enic.com>
Subject: Re: [RFC][PATCH] lru_add_drain_all() don't use schedule_on_each_cpu()

> > On Mon, 2008-10-27 at 12:14 +0900, KOSAKI Motohiro wrote:
> > > > Right, and would be about 4k+sizeof(task_struct), some people might be
> > > > bothered, but most won't care.
> > > > 
> > > > > Perhaps, I misunderstand your intension. so can you point your
> > > > > previous discussion url?
> > > > 
> > > > my google skillz fail me, but once in a while people complain that we
> > > > have too many kernel threads.
> > > > 
> > > > Anyway, if we can re-use this per-cpu workqueue for more goals, I guess
> > > > there is even less of an objection.
> > > 
> > > In general, you are right.
> > > but this is special case. mmap_sem is really widely used various subsystem and drivers.
> > > (because page fault via copy_user introduce to depend on mmap_sem)
> > > 
> > > Then, any work-queue reu-sing can cause similar dead-lock easily.
> > 
> > Yeah, I know, and the cpu-hotplug discussion needed another thread due
> > to yet another locking incident. I was hoping these two could go
> > together.
> 
> Yeah, I found its thread. (I think it is "work_on_cpu: helper for doing task on a CPU.", right?)
> So I'll read it soon.
> 
> Please wait a bit.

Done.

Now, I think smp_call_function() is better for this issue.
I'll try it.

Thanks a lot.

> > Neither are general-purpose workqueues, both need to stay away from the
> > normal eventd due to deadlocks.
> > 
> > ego, does you extra thread ever use mmap_sem?
> 
> 
> 



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