Messages in this thread | | | Date | Wed, 24 Mar 2010 13:33:47 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 07/11] Memory compaction core |
| |
On Tue, 23 Mar 2010 12:25:42 +0000 Mel Gorman <mel@csn.ul.ie> wrote:
> This patch is the core of a mechanism which compacts memory in a zone by > relocating movable pages towards the end of the zone. > > A single compaction run involves a migration scanner and a free scanner. > Both scanners operate on pageblock-sized areas in the zone. The migration > scanner starts at the bottom of the zone and searches for all movable pages > within each area, isolating them onto a private list called migratelist. > The free scanner starts at the top of the zone and searches for suitable > areas and consumes the free pages within making them available for the > migration scanner. The pages isolated for migration are then migrated to > the newly isolated free pages.
General comment: it looks like there are some codepaths which could hold zone->lock for a long time. It's unclear that they're all constrained by COMPACT_CLUSTER_MAX. Is there a a latency issue here?
> > ... > > +static struct page *compaction_alloc(struct page *migratepage, > + unsigned long data, > + int **result) > +{ > + struct compact_control *cc = (struct compact_control *)data; > + struct page *freepage; > + > + VM_BUG_ON(cc == NULL);
It's a bit strange to test this when we're about to oops anyway. The oops will tell us the same thing.
> + /* Isolate free pages if necessary */ > + if (list_empty(&cc->freepages)) { > + isolate_freepages(cc->zone, cc); > + > + if (list_empty(&cc->freepages)) > + return NULL; > + } > + > + freepage = list_entry(cc->freepages.next, struct page, lru); > + list_del(&freepage->lru); > + cc->nr_freepages--; > + > + return freepage; > +}
| |