Re: [PATCH] mm: fix wrong argument of migrate_huge_pages() in soft_offline_huge_page()

[Aneesh Kumar K.V]

David Rientjes <rientjes@xxxxxxxxxx> 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@xxxxxxxxx>
>> > 
>> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
>> > 
>> > 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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