On Thu 03-12-15 11:10:06, Minchan Kim wrote: > On Thu, Dec 03, 2015 at 10:34:04AM +0900, Minchan Kim wrote: > > On Wed, Dec 02, 2015 at 11:16:43AM +0100, Michal Hocko wrote: > > > On Tue 01-12-15 22:34:55, Minchan Kim wrote: > > > > With new test on mmotm-2015-11-25-17-08, I saw below WARNING message > > > > several times. I couldn't see it with reverting new THP refcount > > > > redesign. > > > > > > Just a wild guess. What prevents migration/compaction from calling > > > split_huge_page on thp zero page? There is VM_BUG_ON but it is not clear > > > > I guess migration should work with LRU pages now but zero page couldn't > > stay there. Ahh, you are right. I have missed PageLRU check in isolate_migratepages_block pfn walker. > > > whether you run with CONFIG_DEBUG_VM enabled. > > > > I enabled VM_DEBUG_VM. > > > > > > > > Also, how big is the underflow? [...] > > nr_pages 293 new -324 > > nr_pages 16 new -340 > > nr_pages 342 new -91 > > nr_pages 246 new -337 > > nr_pages 15 new -352 > > nr_pages 15 new -367 They are quite large but that is not that surprising if we consider that we are batching many uncharges at once. > My guess is that it's related to new feature of Kirill's THP 'PageDoubleMap' > so a THP page could be mapped a pte but !pmd_trans_huge(*pmd) so memcg > precharge in move_charge should handle it? I am not familiar with the current state of THP after the rework unfortunately. So if I got you right then you are saying that pmd_trans_huge_lock fails to notice a THP so we will not charge it as THP and only charge one head page and then the tear down path will correctly recognize it as a THP and uncharge the full size, right? I have to admit I have no idea how PageDoubleMap works and how can pmd_trans_huge fail. -- Michal Hocko SUSE Labs -- 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>