linux-kernel - Re: [PATCH] mm: fix wrong argument of migrate_huge_pages() in soft_offline_huge

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Date:	Tue, 17 Jul 2012 15:29:43 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Joonsoo Kim <js1304@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Christoph Lameter <cl@...ux.com>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH] mm: fix wrong argument of migrate_huge_pages() in
 soft_offline_huge_page()

On Tue, 17 Jul 2012, Andrew Morton wrote:

> > > Commit a6bc32b899223a877f595ef9ddc1e89ead5072b8 ('mm: compaction: introduce
> > > sync-light migration for use by compaction') change declaration of
> > > migrate_pages() and migrate_huge_pages().
> > > But, it miss changing argument of migrate_huge_pages()
> > > in soft_offline_huge_page(). In this case, we should call with MIGRATE_SYNC.
> > > So change it.
> > > 
> > > Additionally, there is mismatch between type of argument and function
> > > declaration for migrate_pages(). So fix this simple case, too.
> > > 
> > > Signed-off-by: Joonsoo Kim <js1304@...il.com>
> > 
> > Acked-by: David Rientjes <rientjes@...gle.com>
> > 
> > Should be cc'd to stable for 3.3+.
> 
> Well, why?  I'm suspecting a switch from MIGRATE_SYNC_LIGHT to
> MIGRATE_SYNC will have no discernable effect.  Unless it triggers hitherto
> unknkown about deadlocks...
> 
> For a -stable backport we should have a description of the end-user
> visible effects of the bug.  This changelog lacked such a description.
> 

I would put this:

MIGRATE_SYNC_LIGHT will not aggressively attempt to defragment memory when 
allocating hugepages for migration with MIGRATE_SYNC_LIGHT, such as not 
defragmenting dirty pages, so MADV_SOFT_OFFLINE and 
/sys/devices/system/memory/soft_offline_page would be significantly 
less successful without this patch.
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