Re: [RFC 04/13] mm, page_alloc: restructure direct compaction handling in slowpath

Michal Hocko
2016-05-13T08:31:19Z

On Fri 13-05-16 10:10:50, Vlastimil Babka wrote:
> On 05/12/2016 03:29 PM, Michal Hocko wrote:
> > On Tue 10-05-16 09:35:54, Vlastimil Babka wrote:
> > > This patch attempts to restructure the code with only minimal functional
> > > changes. The call to the first compaction and THP-specific checks are now
> > > placed above the retry loop, and the "noretry" direct compaction is removed.
> > >
> > > The initial compaction is additionally restricted only to costly orders, as we
> > > can expect smaller orders to be held back by watermarks, and only larger orders
> > > to suffer primarily from fragmentation. This better matches the checks in
> > > reclaim's shrink_zones().
> > >
> > > There are two other smaller functional changes. One is that the upgrade from
> > > async migration to light sync migration will always occur after the initial
> > > compaction.
> >
> > I do not think this belongs to the patch. There are two reasons. First
> > we do not need to do potentially more expensive sync mode when async is
> > able to make some progress and the second
>
> My concern was that __GFP_NORETRY non-costly allocations wouldn't otherwise
> get a MIGRATE_SYNC_LIGHT pass at all. Previously they would get it in the
> noretry: label.

OK, I haven't considered this. So scratch this then.
--
Michal Hocko
SUSE Labs