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Date: Fri, 26 Mar 2010 10:03:08 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Mel Gorman <mel@....ul.ie> Cc: Andrew Morton <akpm@...ux-foundation.org>, Andrea Arcangeli <aarcange@...hat.com>, Christoph Lameter <cl@...ux-foundation.org>, Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>, David Rientjes <rientjes@...gle.com>, Minchan Kim <minchan.kim@...il.com>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: Re: [PATCH 10/11] Direct compact when a high-order allocation fails On Thu, 25 Mar 2010 10:16:54 +0000 Mel Gorman <mel@....ul.ie> 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@....ul.ie> 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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