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

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Message-Id: <20111114152100.1333a015.akpm@linux-foundation.org>
Date:	Mon, 14 Nov 2011 15:21:00 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mgorman@...e.de>
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 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...)

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