On Sat, Jan 31, 2015 at 11:58:03PM +0800, Zhang Yanfei wrote: > At 2015/1/30 20:34, Joonsoo Kim wrote: > > From: Joonsoo <iamjoonsoo....@lge.com> > > > > Compaction has anti fragmentation algorithm. It is that freepage > > should be more than pageblock order to finish the compaction if we don't > > find any freepage in requested migratetype buddy list. This is for > > mitigating fragmentation, but, there is a lack of migratetype > > consideration and it is too excessive compared to page allocator's anti > > fragmentation algorithm. > > > > Not considering migratetype would cause premature finish of compaction. > > For example, if allocation request is for unmovable migratetype, > > freepage with CMA migratetype doesn't help that allocation and > > compaction should not be stopped. But, current logic regards this > > situation as compaction is no longer needed, so finish the compaction. > > > > Secondly, condition is too excessive compared to page allocator's logic. > > We can steal freepage from other migratetype and change pageblock > > migratetype on more relaxed conditions in page allocator. This is designed > > to prevent fragmentation and we can use it here. Imposing hard constraint > > only to the compaction doesn't help much in this case since page allocator > > would cause fragmentation again. > > Changing both two behaviours in compaction may change the high order > allocation > behaviours in the buddy allocator slowpath, so just as Vlastimil suggested, > some data from allocator should be necessary and helpful, IMHO.
As Vlastimil said, fragmentation effect should be checked. I will do it and report the result on next version. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
