On Thu, 25 Mar 2010 10:16:54 +0000 Mel Gorman <mel@xxxxxxxxx> wrote: > On Thu, Mar 25, 2010 at 06:50:21PM +0900, KAMEZAWA Hiroyuki wrote: > > On Thu, 25 Mar 2010 09:48:26 +0000 > > Mel Gorman <mel@xxxxxxxxx> wrote: > > > > > > In that case, compact_finished() can't > > > > find there is a free chunk and do more work. How about using a function like > > > > free_pcppages_bulk(zone, pcp->batch, pcp); > > > > to bypass pcp list and freeing pages at once ? > > > > > > > > > > I think you mean to drain the PCP lists while compaction is happening > > > but is it justified? It's potentially a lot of IPI calls just to check > > > if compaction can finish a little earlier. If the pages on the PCP lists > > > are making that much of a difference to high-order page availability, it > > > implies that the zone is pretty full and it's likely that compaction was > > > avoided and we direct reclaimed. > > > > > Ah, sorry for my short word again. I mean draining "local" pcp list because > > a thread which run direct-compaction freed pages. IPI is not necessary and > > overkill. > > > > Ah, I see now. There are two places that pages get freed. release_freepages() > at the end of compaction when it's too late for compact_finished() to be > helped and within migration itself. Migration frees with either > free_page() or more commonly put_page() with put_page() being the most > frequently used. As free_page() is called on failure to migrate (rare), > there is little help in changing it and I'd rather not modify how > put_page() works. > > I could add a variant of drain_local_pages() that drains just the local PCP of > a given zone before compact_finished() is called. The cost would be a doubling > of the number of times zone->lock is taken to do the drain. Is it > justified? It seems overkill to me to take the zone->lock just in case > compaction can finish a little earlier. It feels like it would be adding > a guaranteed cost for a potential saving. > If you want to keep code comapct, I don't ask more. I worried about that just because memory hot-unplug were suffered by pagevec and pcp list before using MIGRATE_ISOLATE and proper lru_add_drain(). Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>