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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC][PATCH] lru_add_drain_all() don't use schedule_on_each_cpu()
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> 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.


> 
> 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?