Hi Vlastimil, Thanks for comment. On 2017/3/13 17:51, Vlastimil Babka wrote: > On 03/10/2017 10:53 AM, Yisheng Xie wrote: >> Hi Vlastimil, >> >> Thanks for comment. >> On 2017/3/10 15:30, Vlastimil Babka wrote: >>> On 03/10/2017 05:20 AM, Yisheng Xie wrote: >>>> If the migrate target is a large free page and we ignore suitable, >>>> it may not good for defrag. So move the ignore block suitable after >>>> check large free page. >>> >>> Right. But in practice I expect close to no impact, because direct >>> compaction shouldn't have to be called if there's a >=pageblock_order >>> page already available. >>> >> Maybe you are right and this change is just based on logical analyses. > > I'm not opposing the change, it might be better for future-proofing the > function, just pointing out that it most likely won't have any visible > effect right now. Get it, maybe I should put these in the change log :) > >> Presently, only in direct compaction, we increase the compaction priority, >> and ignore suitable at MIN_COMPACT_PRIORITY. I have a silly question, can >> we do the similar thing in kcompactd? maybe by doing most work in kcompactd, >> we can get better perf of slow path. > > That would need a very good evaluation at the very least. Migrating > pages into pageblocks other than movable ones brings the danger of later > unmovable/reclaimable allocations having to fallback to movable > pageblocks and causing permanent fragmentation. For direct compaction we > decided that it's better to risk permanent fragmentation than a > premature OOM, but for kcompactd there doesn't seem to be such > compelling reason. Thanks for kindly explain. > >> Thanks >> Yisheng Xie -- 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>
