Re: [PATCH v4 06/11] mm/migrate: make a standard migration target allocation function

[Joonsoo Kim]

2020ë 7ì 8ì (ì) ìì 4:00, Michal Hocko <mhocko@xxxxxxxxxx>ëì ìì:
>
> On Tue 07-07-20 16:49:51, Vlastimil Babka wrote:
> > On 7/7/20 9:44 AM, js1304@xxxxxxxxx wrote:
> > > From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > >
> > > There are some similar functions for migration target allocation.  Since
> > > there is no fundamental difference, it's better to keep just one rather
> > > than keeping all variants.  This patch implements base migration target
> > > allocation function.  In the following patches, variants will be converted
> > > to use this function.
> > >
> > > Changes should be mechanical but there are some differences. First, Some
> > > callers' nodemask is assgined to NULL since NULL nodemask will be
> > > considered as all available nodes, that is, &node_states[N_MEMORY].
> > > Second, for hugetlb page allocation, gfp_mask is ORed since a user could
> > > provide a gfp_mask from now on.
> >
> > I think that's wrong. See how htlb_alloc_mask() determines between
> > GFP_HIGHUSER_MOVABLE and GFP_HIGHUSER, but then you OR it with __GFP_MOVABLE so
> > it's always GFP_HIGHUSER_MOVABLE.

Indeed.

> Right you are! Not that it would make any real difference because only
> migrateable hugetlb pages will get __GFP_MOVABLE and so we shouldn't
> really end up here for !movable pages in the first place (not sure about
> soft offlining at this moment). But yeah it would be simply better to
> override gfp mask for hugetlb which we have been doing anyway.

Override gfp mask doesn't work since some users will call this function with
__GFP_THISNODE.  I will use hugepage_movable_supported() here and
clear __GFP_MOVABLE if needed.

Thanks.

Thanks.