On Thu, Oct 13, 2016 at 01:05:11PM +0200, Vlastimil Babka wrote: > On 10/13/2016 10:08 AM, js1304@xxxxxxxxx wrote: > >From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > > >We have migratetype facility to minimise fragmentation. It dynamically > >changes migratetype of pageblock based on some criterias but it never > >be perfect. Some migratetype pages are often placed in the other > >migratetype pageblock. We call this pageblock as mixed pageblock. > > > >There are two types of mixed pageblock. Movable page on unmovable > >pageblock and unmovable page on movable pageblock. (I simply ignore > >reclaimble migratetype/pageblock for easy explanation.) Earlier case is > >not a big problem because movable page is reclaimable or migratable. We can > >reclaim/migrate it when necessary so it usually doesn't contribute > >fragmentation. Actual problem is caused by later case. We don't have > >any way to reclaim/migrate this page and it prevents to make high order > >freepage. > > > >This later case happens when there is too less unmovable freepage. When > >unmovable freepage runs out, fallback allocation happens and unmovable > >allocation would be served by movable pageblock. > > > >To solve/prevent this problem, we need to have enough unmovable freepage > >to satisfy all unmovable allocation request by unmovable pageblock. > >If we set enough unmovable pageblock at boot and fix it's migratetype > >until power off, we would have more unmovable freepage during runtime and > >mitigate above problem. > > > >This patch provides a way to set minimum number of unmovable pageblock > >at boot time. In my test, with proper setup, I can't see any mixed > >pageblock where unmovable allocation stay on movable pageblock. > > So if I get this correctly, the fixed-as-unmovable bit doesn't > actually prevent fallbacks to such pageblocks? Then I'm surprised > that's enough to make any difference. Also Johannes's problem is > that there are too many unmovable pageblocks, so I'm a bit skeptical > that simply preallocating some will help his workload. But we'll > see... This patch standalone would not help the Johannes's problem, but, with whole series, it would make some difference. I started this series motivated from Johannes's report but it doesn't totally focus on his problem. Our android system also has a long standing fragmentation problem and I hope that this patchset would help them, too. > > In any case I wouldn't pursue a solution that requires user > configuration, until as a last resort. Hopefully we can make the > heuristics good enough so that's not necessary. Sorry for my mostly > negative feedback to your series, I'm glad you pursuit this as well, > and hope we'll eventually find a good solution :) I'm fine with your feedback. It's valuable. I also doesn't pursue the method that requires your configuration but it would be the case that it is necessary. Amount of allocation request with specific migratetype on our system varies a lot. Migratetype of pageblock would be changed frequently in this situation and frequent changing migratetype would increase mixed pageblock and cause permanent fragmentation. 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>