linux-kernel - Re: [PATCH] mm: Reduce the amount of work done when updating min_free

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Message-ID: <20111115122315.GD27150@suse.de>
Date:	Tue, 15 Nov 2011 12:23:15 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: Reduce the amount of work done when updating
 min_free_kbytes

On Mon, Nov 14, 2011 at 03:21:00PM -0800, Andrew Morton wrote:
> On Fri, 11 Nov 2011 16:21:19 +0000
> Mel Gorman <mgorman@...e.de> wrote:
> 
> > When min_free_kbytes is updated, some pageblocks are marked MIGRATE_RESERVE.
> > Ordinarily, this work is unnoticable as it happens early in boot but on
> > large machines with 1TB of memory, this has been reported to delay
> > boot times, probably due to the NUMA distances involved.
> > 
> > The bulk of the work is due to calling calling pageblock_is_reserved()
> > an unnecessary amount of times and accessing far more struct page
> > metadata than is necessary. This patch significantly reduces the
> > amount of work done by setup_zone_migrate_reserve() improving boot
> > times on 1TB machines.
> > 
> 
> By how much? :)
> 
> (I mainly ask because I'm curious to know how long the kernel takes to
> boot on a 1TB machine...)
> 


Good question. I don't have access to the machine but based on the dmesg
they posted before and after, this patch reduced boot times by 27
seconds.

With only dmesg, I don't know how long it is taking to start services
and mount of the filesystem but assuming no major problems or timeouts
from drivers it looks like it is taking about 6 minutes to boot.

-- 
Mel Gorman
SUSE Labs
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