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Date: Tue, 28 Oct 2008 13:45:36 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: kosaki.motohiro@jp.fujitsu.com, heiko.carstens@de.ibm.com, npiggin@suse.de,
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       torvalds@linux-foundation.org, riel@redhat.com, lee.schermerhorn@hp.com,
       linux-mm@kvack.org
Subject: Re: [RFC][PATCH] lru_add_drain_all() don't use
 schedule_on_each_cpu()
Message-Id: <20081028134536.9a7a5351.akpm@linux-foundation.org>
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On Tue, 28 Oct 2008 09:25:31 -0500 (CDT)
Christoph Lameter <cl@linux-foundation.org> wrote:

> On Mon, 27 Oct 2008, Andrew Morton wrote:
> 
> > Can we fix that instead?
> 
> How about this fix?
> 
> 
> 
> Subject: Move migrate_prep out from under mmap_sem
> 
> Move the migrate_prep outside the mmap_sem for the following system calls
> 
> 1. sys_move_pages
> 2. sys_migrate_pages
> 3. sys_mbind()
> 
> It really does not matter when we flush the lru. The system is free to add
> pages onto the lru even during migration which will make the page 
> migration either skip the page (mbind, migrate_pages) or return a busy 
> state (move_pages).
> 

That looks nicer, thanks.  Hopefully it fixes the
lockdep-warning/deadlock...

I guess we should document our newly discovered schedule_on_each_cpu()
problems before we forget about it and later rediscover it.