On Mon, May 12, 2014 at 11:09:25AM +0200, Vlastimil Babka wrote: > On 05/08/2014 07:28 AM, Joonsoo Kim wrote: > >On Wed, May 07, 2014 at 02:09:10PM +0200, Vlastimil Babka wrote: > >>The compaction free scanner in isolate_freepages() currently remembers PFN of > >>the highest pageblock where it successfully isolates, to be used as the > >>starting pageblock for the next invocation. The rationale behind this is that > >>page migration might return free pages to the allocator when migration fails > >>and we don't want to skip them if the compaction continues. > >> > >>Since migration now returns free pages back to compaction code where they can > >>be reused, this is no longer a concern. This patch changes isolate_freepages() > >>so that the PFN for restarting is updated with each pageblock where isolation > >>is attempted. Using stress-highalloc from mmtests, this resulted in 10% > >>reduction of the pages scanned by the free scanner. > > > >Hello, > > > >Although this patch could reduce page scanned, it is possible to skip > >scanning fresh pageblock. If there is zone lock contention and we are on > >asyn compaction, we stop scanning this pageblock immediately. And > >then, we will continue to scan next pageblock. With this patch, > >next_free_pfn is updated in this case, so we never come back again to this > >pageblock. Possibly this makes compaction success rate low, doesn't > >it? > > Hm, you're right and thanks for catching that, but I think this is a > sign of a worse and older issue than skipping a pageblock? > When isolate_freepages_block() breaks loop due to lock contention, > then isolate_freepages() (which called it) should also immediately > quit its loop. Trying another pageblock in the same zone with the > same zone->lock makes no sense here? If this is fixed, then the > issue you're pointing out will also be fixed as next_free_pfn will > still point to the pageblock where the break occured. > Yes. It can be fixed by your approach. :) Thanks. -- 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>