On 02/02/2015 02:23 PM, Joonsoo Kim wrote: > 2015-02-02 19:20 GMT+09:00 Vlastimil Babka <vbabka@xxxxxxx>: >> On 02/02/2015 08:15 AM, Joonsoo Kim wrote: >> >> So I've realized that this problaby won't always work as intended :/ Because we >> still differ from what page allocator does. >> Consider we compact for UNMOVABLE allocation. First we try RECLAIMABLE fallback. >> Turns out we could fallback, but not steal, hence we skip it due to >> only_stealable == true. So we try MOVABLE, and turns out we can steal, so we >> finish compaction. >> Then the allocation attempt follows, and it will fallback to RECLAIMABLE, >> without extra stealing. The compaction decision for MOVABLE was moot. >> Is it a big problem? Probably not, the compaction will still perform some extra >> anti-fragmentation on average, but we should consider it. > > Hello, > > First of all, thanks for quick review. :) > > Hmm... I don't get it. Is this case possible in current implementation? > can_steal_fallback() decides whether steal is possible or not, based > on freepage order > and start_migratetype. If fallback freepage is on RECLAIMABLE and > MOVABLE type and > they are same order, can_steal could be true for both or false for > neither. If order is > different, compaction decision would be recognized by > __rmqueue_fallback() since it > try to find freepage from high order to low order. Ah, right, I got confused into thinking that the result of can_steal depends on how many freepages it found within the pageblock to steal. Sorry about the noise. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>