On Mon 19-02-24 20:37:17, Donet Tom wrote:
>
> On 2/19/24 19:50, Michal Hocko wrote:
> > On Sat 17-02-24 01:31:35, Donet Tom wrote:
> > [...]
> > > +static inline bool mpol_preferred_should_numa_migrate(int exec_node, int folio_node,
> > > + struct mempolicy *pol)
> > > +{
> > > + /* if the executing node is in the policy node mask, migrate */
> > > + if (node_isset(exec_node, pol->nodes))
> > > + return true;
> > > +
> > > + /* If the folio node is in policy node mask, don't migrate */
> > > + if (node_isset(folio_node, pol->nodes))
> > > + return false;
> > > + /*
> > > + * both the folio node and executing node are outside the policy nodemask,
> > > + * migrate as normal numa fault migration.
> > > + */
> > > + return true;
> > > +}
> > I have looked at this again and only now noticed that this doesn't
> > really work as one would expected.
> >
> > case MPOL_PREFERRED_MANY:
> > /*
> > * use current page if in policy nodemask,
> > * else select nearest allowed node, if any.
> > * If no allowed nodes, use current [!misplaced].
> > */
> > if (node_isset(curnid, pol->nodes))
> > goto out;
> > z = first_zones_zonelist(
> > node_zonelist(numa_node_id(), GFP_HIGHUSER),
> > gfp_zone(GFP_HIGHUSER),
> > &pol->nodes);
> > polnid = zone_to_nid(z->zone);
> > break;
> >
> > Will collapse the whole MPOL_PREFERRED_MANY nodemask into the first
> > notde into that mask. Is that really what we want here? Shouldn't we use
> > the full nodemask as the migration target?
>
> With this patch it will take full nodemask and find out the correct migration target. It will not collapse into first node.
Correct me if I am wrong, but mpol_misplaced will return the first node
of the preffered node mask and then migrate_misplaced_folio would use
it as a target node for alloc_misplaced_dst_folio which performs
__GFP_THISNODE allocation so it won't fall back to a different node.
--
Michal Hocko
SUSE Labs
