Messages in this thread | | | Date | Mon, 20 Oct 2014 11:44:18 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH 5/5] mm, compaction: more focused lru and pcplists draining |
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On 10/07/2014 11:33 AM, Vlastimil Babka wrote: > The goal of memory compaction is to create high-order freepages through page > migration. Page migration however puts pages on the per-cpu lru_add cache, > which is later flushed to per-cpu pcplists, and only after pcplists are > drained the pages can actually merge. This can happen due to the per-cpu > caches becoming full through further freeing, or explicitly. > > During direct compaction, it is useful to do the draining explicitly so that > pages merge as soon as possible and compaction can detect success immediately > and keep the latency impact at minimum. However the current implementation is > far from ideal. Draining is done only in __alloc_pages_direct_compact(), > after all zones were already compacted, and the decisions to continue or stop > compaction in individual zones was done without the last batch of migrations > being merged. It is also missing the draining of lru_add cache before the > pcplists. > > This patch moves the draining for direct compaction into compact_zone(). It > adds the missing lru_cache draining and uses the newly introduced single zone > pcplists draining to reduce overhead and avoid impact on unrelated zones. > Draining is only performed when it can actually lead to merging of a page of > desired order (passed by cc->order). This means it is only done when migration > occurred in the previously scanned cc->order aligned block(s) and the > migration scanner is now pointing to the next cc->order aligned block.
Acked-by: Rik van Riel <riel@redhat.com>
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