[Devel] Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag

[Mel Gorman]

On Tue, Sep 18, 2012 at 06:04:02PM +0400, Glauber Costa wrote:
> This flag is used to indicate to the callees that this allocation is a
> kernel allocation in process context, and should be accounted to
> current's memcg. It takes numerical place of the of the recently removed
> __GFP_NO_KSWAPD.
> 
> Signed-off-by: Glauber Costa <glommer at parallels.com>
> CC: Christoph Lameter <cl at linux.com>
> CC: Pekka Enberg <penberg at cs.helsinki.fi>
> CC: Michal Hocko <mhocko at suse.cz>
> CC: Johannes Weiner <hannes at cmpxchg.org>
> CC: Suleiman Souhlal <suleiman at google.com>
> CC: Rik van Riel <riel at redhat.com>
> CC: Mel Gorman <mel at csn.ul.ie>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>

I agree with Christophs recommendation that this flag always exist instead
of being 0 in the !MEMCG_KMEM case. If __GFP_KMEMCG ever is used in another
part of the VM (which would be unexpected but still) then the behaviour
might differ too much between MEMCG_KMEM and !MEMCG_KMEM cases. As unlikely
as the case is, it's not impossible.

For tracing __GFP_KMEMCG should have an entry in
include/trace/events/gfpflags.h

Get rid of the CONFIG_MEMCG_KMEM check and update
include/trace/events/gfpflags.h and then feel free to stick my Acked-by
on it.

-- 
Mel Gorman
SUSE Labs