linux-kernel - Re: [PATCH] Add ability to dump mapped pages with /proc/sys/vm/drop

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Message-ID: <20071001033605.GA11497@redhat.com>
Date:	Sun, 30 Sep 2007 23:36:05 -0400
From:	Dave Jones <davej@...hat.com>
To:	Soeren Sandmann <sandmann@...mi.au.dk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Add ability to dump mapped pages with
	/proc/sys/vm/drop_caches

On Sun, Sep 30, 2007 at 08:03:51PM +0200, Soeren Sandmann wrote:
 > This patch adds the ability to drop mapped pages with
 > /proc/sys/vm/drop_caches. This is useful to get repeatable
 > measurements of startup time for applications. 
 > 
 > Without it, pages that are mapped in already-running applications will
 > not get dropped, so the time measured will not be a true cold-cache
 > time.
 > 
 > Rik pointed out that "be_atomic" is a bit pointless since there is a
 > race on SMP anyway where pages can be added. However, it is there in
 > the existing code, so I added it for the new code as well. Does anyone
 > know why it's there?
 
this cset added it (and has a pretty explanatory commit msg)

	Dave

commit fc9a07e7bf1a76e710f5df017abb07628db1781d
Author: Andrew Morton <akpm@...ux-foundation.org>
Date:   Sun Jul 15 23:38:14 2007 -0700

    invalidate_mapping_pages(): add cond_resched
    
    invalidate_mapping_pages() can sometimes take a long time (millions of pages
    to free).  Long enough for the softlockup detector to trigger.
    
    We used to have a cond_resched() in there but I took it out because the
    drop_caches code calls invalidate_mapping_pages() under inode_lock.
    
    The patch adds a nasty flag and puts the cond_resched() back.



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