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

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Message-Id: <20081027120405.1B45.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Mon, 27 Oct 2008 12:14:52 +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()

> 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.


So I think we have two choices (nick explained it at this thread).

(1) own workqueue (the patch)
(2) avoid lru_add_drain_all completely


if you really strongly hate (1), we should target to (2) IMO.

Thought?



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