First off, sorry for the long delay getting back to you. I was sick for
a few weeks and still catching up. I'm still not 100%.
On Thu, Dec 08, 2022 at 05:51:11PM +0100, Vlastimil Babka wrote:
> On 11/29/22 16:16, Mel Gorman wrote:
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index da746e9eb2cf..e2b65767dda0 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3710,7 +3710,7 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
> > * reserved for high-order atomic allocation, so order-0
> > * request should skip it.
> > */
> > - if (order > 0 && alloc_flags & ALLOC_HARDER)
> > + if (alloc_flags & ALLOC_HIGHATOMIC)
> > page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
> > if (!page) {
> > page = __rmqueue(zone, order, migratetype, alloc_flags);
> > @@ -4028,8 +4028,10 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
> > return true;
> > }
> > #endif
> > - if (alloc_harder && !free_area_empty(area, MIGRATE_HIGHATOMIC))
> > + if ((alloc_flags & ALLOC_HIGHATOMIC) &&
> > + !free_area_empty(area, MIGRATE_HIGHATOMIC)) {
> > return true;
>
> alloc_harder is defined as
> (alloc_flags & (ALLOC_HARDER|ALLOC_OOM));
> AFAICS this means we no longer allow ALLOC_OOM to use the highatomic
> reserve. Isn't that a risk?
>
Yes, it is. I intend to apply the patch below on top. I didn't alter the
first check for ALLOC_HIGHATOMIC as I wanted OOM handling to only use the
high-order reserves if there was no other option. While this is a change
in behaviour, it should be a harmless one. I'll add a note in the changelog.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 50fc1e7cb154..0ef4f3236a5a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3710,6 +3710,16 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
if (!page) {
page = __rmqueue(zone, order, migratetype, alloc_flags);
+
+ /*
+ * If the allocation fails, allow OOM handling access
+ * to HIGHATOMIC reserves as failing now is worse than
+ * failing a high-order atomic allocation in the
+ * future.
+ */
+ if (!page && (alloc_flags & ALLOC_OOM))
+ page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
+
if (!page) {
spin_unlock_irqrestore(&zone->lock, flags);
return NULL;
@@ -4023,7 +4033,7 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
return true;
}
#endif
- if ((alloc_flags & ALLOC_HIGHATOMIC) &&
+ if ((alloc_flags & (ALLOC_HIGHATOMIC|ALLOC_OOM)) &&
!free_area_empty(area, MIGRATE_HIGHATOMIC)) {
return true;
}
--
Mel Gorman
SUSE Labs
