| Message ID | 20200630142639.22770-6-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm / virtio-mem: support ZONE_MOVABLE | expand |
On 30.06.20 16:26, David Hildenbrand wrote: > We can already have pages that can be offlined but not allocated in > ZONE_MOVABLE - PageHWPoison pages. While these pages can be skipped when > offlining ("moving them to /dev/null"), we cannot move them when > allocating. > > virtio-mem managed memory is similar. The logical memory holes > corresponding to unplug memory ranges can be skipped when offlining, > however, the pages cannot be moved. Currently, virtio-mem special-cases > ZONE_MOVABLE, such that: > - partially plugged memory blocks it added to Linux cannot be onlined to > ZONE_MOVABLE > - when unplugging memory, it will never consider memory blocks that were > onlined to ZONE_MOVABLE > > We also want to support ZONE_MOVABLE in virtio-mem for both cases. Note > that virtio-mem does not blindly try to unplug random pages within its > managed memory region. It always plugs memory left-to-right and tries to > unplug memory right-to-left - in roughly MAX_ORDER - 1 granularity. In > theory, the movable ZONE part would only shrink when unplugging memory > from ZONE_MOVABLE. > > Let's perform the ZONE_MOVABLE optimization only for memory offlining, > such that we reduce the number of false positives from > has_unmovable_pages() in case of alloc_contig_range() on ZONE_MOVABLE. > > Note: We currently don't seem to have any user of alloc_contig_range() > that actually uses ZONE_MOVABLE. This change is mostly valuable for the > documentation. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Michal Hocko <mhocko@suse.com> > Cc: Michael S. Tsirkin <mst@redhat.com> > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > mm/page_alloc.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index bd3ebf08f09b9..45077d74d975d 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -8237,9 +8237,12 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page, > /* > * If the zone is movable and we have ruled out all reserved > * pages then it should be reasonably safe to assume the rest > - * is movable. > + * is movable. As we can have some pages in the movable zone > + * that are only considered movable for memory offlining (esp., > + * PageHWPoison and PageOffline that will be skipped), we > + * perform this optimization only for memory offlining. > */ > - if (zone_idx(zone) == ZONE_MOVABLE) > + if ((flags & MEMORY_OFFLINE) && zone_idx(zone) == ZONE_MOVABLE) > continue; > > /* > So, as we don't have any alloc_contig_range() users that use ZONE_MOVABLE for now, and virtio-mem will be the only one for now (which accounts for 50% of the special cases - PG_offline), I think we might drop this patch. Worst think is that if we ever have other alloc_contig_range() users, that we return "false" from has_unmovable_pages() and fail later when trying to migrate/isolate all pages. This should, however, only happen in rare cases (and there are already other cases where we have basically unmovable data - long-term pinnings). On the plus side, keeping the ZONE_MOVABLE optimizations here also allows virtio-mem to better tolerate unstable page flags when trying to alloc_contig_range(). Thoughts?
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index bd3ebf08f09b9..45077d74d975d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8237,9 +8237,12 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page, /* * If the zone is movable and we have ruled out all reserved * pages then it should be reasonably safe to assume the rest - * is movable. + * is movable. As we can have some pages in the movable zone + * that are only considered movable for memory offlining (esp., + * PageHWPoison and PageOffline that will be skipped), we + * perform this optimization only for memory offlining. */ - if (zone_idx(zone) == ZONE_MOVABLE) + if ((flags & MEMORY_OFFLINE) && zone_idx(zone) == ZONE_MOVABLE) continue; /*
We can already have pages that can be offlined but not allocated in ZONE_MOVABLE - PageHWPoison pages. While these pages can be skipped when offlining ("moving them to /dev/null"), we cannot move them when allocating. virtio-mem managed memory is similar. The logical memory holes corresponding to unplug memory ranges can be skipped when offlining, however, the pages cannot be moved. Currently, virtio-mem special-cases ZONE_MOVABLE, such that: - partially plugged memory blocks it added to Linux cannot be onlined to ZONE_MOVABLE - when unplugging memory, it will never consider memory blocks that were onlined to ZONE_MOVABLE We also want to support ZONE_MOVABLE in virtio-mem for both cases. Note that virtio-mem does not blindly try to unplug random pages within its managed memory region. It always plugs memory left-to-right and tries to unplug memory right-to-left - in roughly MAX_ORDER - 1 granularity. In theory, the movable ZONE part would only shrink when unplugging memory from ZONE_MOVABLE. Let's perform the ZONE_MOVABLE optimization only for memory offlining, such that we reduce the number of false positives from has_unmovable_pages() in case of alloc_contig_range() on ZONE_MOVABLE. Note: We currently don't seem to have any user of alloc_contig_range() that actually uses ZONE_MOVABLE. This change is mostly valuable for the documentation. Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> --- mm/page_alloc.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)