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

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Message-ID: <87ipdlcwnm.fsf@skywalker.in.ibm.com>
Date:	Wed, 18 Jul 2012 13:45:41 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	David Rientjes <rientjes@...gle.com>,
	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()

David Rientjes <rientjes@...gle.com> writes:

> 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.

Is that true with hugetlb pages ? hugetlbfs_migrate_page doesn't seem to
use the mode argument at all. We do look at MIGRATE_SYNC if we fail to
get page lock, but other than that do we look at mode argument for
hugetlb pages ?

-aneesh

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