Am Freitag, den 18.03.2016, 21:58 +0100 schrieb Vlastimil Babka: > On 03/18/2016 03:42 PM, Lucas Stach wrote: > > Am Freitag, den 18.03.2016, 15:10 +0100 schrieb Vlastimil Babka: > >> On 03/17/2016 04:52 PM, Joonsoo Kim wrote: > >> > 2016-03-18 0:43 GMT+09:00 Vlastimil Babka <vbabka@xxxxxxx>: > >> > >> OK, here it is. Hanjun can you please retest this, as I'm not sure if you had > >> the same code due to the followup one-liner patches in the thread. Lucas, see if > >> it helps with your issue as well. Laura and Joonsoo, please also test and review > >> and check changelog if my perception of the problem is accurate :) > >> > > > > This doesn't help for my case, as it is still trying to merge pages in > > isolated ranges. It even tries extra hard at doing so. > > > > With concurrent isolation and frees going on this may lead to the start > > page of the range to be isolated merging into an higher order buddy page > > if it isn't already pageblock aligned, leading both test_pages_isolated > > and isolate_freepages to fail on an otherwise perfectly fine range. > > > > What I am arguing is that if a page is freed into an isolated range we > > should not try merge it with it's buddies at all, by setting max_order = > > order. If the range is isolated because want to isolate freepages from > > it, the work to do the merging is wasted, as isolate_freepages will > > split higher order pages into order-0 pages again. > > > > If we already finished isolating freepages and are in the process of > > undoing the isolation, we don't strictly need to do the merging in > > __free_one_page, but can defer it to unset_migratetype_isolate, allowing > > to simplify those code paths by disallowing any merging of isolated > > pages at all. > > Oh, I think understand now. Yeah, skipping merging for pages in isolated > pageblocks might be a rather elegant solution. But still, we would have to check > buddy's migratetype at order >= pageblock_order like my patch does, which is > annoying. Because even without isolated merging, the buddy might have already > had order>=pageblock_order when it was isolated. > So what if isolation also split existing buddies in the pageblock immediately > when it sets the MIGRATETYPE_ISOLATE on the pageblock? Then we would have it > guaranteed that there's no isolated buddy - a buddy candidate at order >= > pageblock_order either has a smaller order (so it's not a buddy) or is not > MIGRATE_ISOLATE so it's safe to merge with. > > Does that make sense? > This might increase the the overhead of isolation a lot. CMA is also used for small order allocations, so the work of splitting a whole pageblock to allocate a small number of pages out just to merge a lot of them again on unisolation might make this unattractive. My feeling is that checking the buddy migratetype for >=pageblock_order frees might be lower overhead, but I have no hard numbers to back this claim. Then on the other hand moving the work to isolation/unisolation affects only code paths that are expected to be quite slow anyways, doing the check in _free_one_page will affect everyone. Regards, Lucas -- 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>