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From: Andrea Arcangeli <aarcange@redhat.com>
To: Minchan Kim <minchan.kim@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Mel Gorman <mel@csn.ul.ie>,
	Andrew Morton <akpm@linux-foundation.org>,
	Arthur Marsh <arthur.marsh@internode.on.net>,
	Clemens Ladisch <cladisch@googlemail.com>,
	Linux-MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] mm: compaction: Minimise the time IRQs are disabled while isolating pages for migration
Date: Tue, 1 Mar 2011 17:19:00 +0100	[thread overview]
Message-ID: <20110301161900.GA21860@random.random> (raw)
In-Reply-To: <20110301153558.GA2031@barrios-desktop>

On Wed, Mar 02, 2011 at 12:35:58AM +0900, Minchan Kim wrote:
> On Tue, Mar 01, 2011 at 01:49:25PM +0900, KAMEZAWA Hiroyuki wrote:
> > On Tue, 1 Mar 2011 13:11:46 +0900
> > Minchan Kim <minchan.kim@gmail.com> wrote:
> > 
> > > On Tue, Mar 01, 2011 at 08:42:09AM +0900, KAMEZAWA Hiroyuki wrote:
> > > > On Mon, 28 Feb 2011 10:18:27 +0000
> > > > Mel Gorman <mel@csn.ul.ie> wrote:
> > > > 
> > > > > > BTW, can't we drop disable_irq() from all lru_lock related codes ?
> > > > > > 
> > > > > 
> > > > > I don't think so - at least not right now. Some LRU operations such as LRU
> > > > > pagevec draining are run from IPI which is running from an interrupt so
> > > > > minimally spin_lock_irq is necessary.
> > > > > 
> > > > 
> > > > pagevec draining is done by workqueue(schedule_on_each_cpu()). 
> > > > I think only racy case is just lru rotation after writeback.
> > > 
> > > put_page still need irq disable.
> > > 
> > 
> > Aha..ok. put_page() removes a page from LRU via __page_cache_release().
> > Then, we may need to remove a page from LRU under irq context.
> > Hmm...
> 
> But as __page_cache_release's comment said, normally vm doesn't release page in
> irq context. so it would be rare.
> If we can remove it, could we change all of spin_lock_irqsave with spin_lock?
> If it is right, I think it's very desirable to reduce irq latency.
> 
> How about this? It's totally a quick implementation and untested. 
> I just want to hear opinions of you guys if the work is valuable or not before
> going ahead.

pages freed from irq shouldn't be PageLRU.

deferring freeing to workqueue doesn't look ok. firewall loads runs
only from irq and this will cause some more work and a delay in the
freeing. I doubt it's worhwhile especially for the lru_lock.

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  reply	other threads:[~2011-03-01 16:19 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-03-01 15:35 [PATCH 2/2] mm: compaction: Minimise the time IRQs are disabled while isolating pages for migration Minchan Kim
2011-03-01 16:19 ` Andrea Arcangeli [this message]
2011-03-01 22:22   ` Minchan Kim
2011-03-01 22:34     ` Andrew Morton
2011-03-01 22:57       ` Minchan Kim
  -- strict thread matches above, loose matches on Subject: below --
2011-02-25 20:04 [PATCH 0/2] Reduce the amount of time compaction disables IRQs for V2 Mel Gorman
2011-02-25 20:04 ` [PATCH 2/2] mm: compaction: Minimise the time IRQs are disabled while isolating pages for migration Mel Gorman
2011-02-25 22:32   ` Johannes Weiner
2011-02-26  0:16     ` Andrea Arcangeli
2011-02-28  2:17   ` KAMEZAWA Hiroyuki
2011-02-28  5:48     ` Andrea Arcangeli
2011-02-28  5:54       ` KAMEZAWA Hiroyuki
2011-02-28  9:28         ` Mel Gorman
2011-02-28  9:42           ` KAMEZAWA Hiroyuki
2011-02-28 10:18             ` Mel Gorman
2011-02-28 23:42               ` KAMEZAWA Hiroyuki
2011-03-01  4:11                 ` Minchan Kim
2011-03-01  4:49                   ` KAMEZAWA Hiroyuki
2011-02-28 23:01   ` Minchan Kim
2011-02-28 23:07     ` Andrea Arcangeli
2011-02-28 23:25       ` Minchan Kim
2011-03-01 22:15   ` Andrew Morton
2011-02-25 18:00 [PATCH 0/2] Reduce the amount of time compaction disables IRQs for Mel Gorman
2011-02-25 18:00 ` [PATCH 2/2] mm: compaction: Minimise the time IRQs are disabled while isolating pages for migration Mel Gorman

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