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

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Date:	Sun, 26 Oct 2008 14:49:06 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	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 Sun, 2008-10-26 at 22:37 +0900, KOSAKI Motohiro wrote:
> Hi Peter,
> 
> >> @@ -611,4 +613,8 @@ void __init swap_setup(void)
> >>  #ifdef CONFIG_HOTPLUG_CPU
> >>       hotcpu_notifier(cpu_swap_callback, 0);
> >>  #endif
> >> +
> >> +     vm_wq = create_workqueue("vm_work");
> >> +     BUG_ON(!vm_wq);
> >> +
> >>  }
> >
> > While I really hate adding yet another per-cpu thread for this, I don't
> > see another way out atm.
> 
> Can I ask the reason of your hate?
> if I don't know it, making improvement patch is very difficult to me.

There seems to be no drive to keep them down, ps -def output it utterly
dominated by kernel threads on a freshly booted machine with many cpus.

And while they are not _that_ expensive to have around, they are not
free either, I imagine the tiny-linux folks having an interest in
keeping these down too.

> > Oleg, Rusty, ego, you lot were discussing a similar extra per-cpu
> > workqueue, can we merge these two?
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