On Fri, Dec 04, 2015 at 09:52:27AM +0100, Michal Hocko wrote: > On Fri 04-12-15 14:35:15, Minchan Kim wrote: > > On Thu, Dec 03, 2015 at 04:47:29PM +0100, Michal Hocko wrote: > > > On Thu 03-12-15 15:58:50, Michal Hocko wrote: > > > [....] > > > > Warning, this looks ugly as hell. > > > > > > I was thinking about it some more and it seems that we should rather not > > > bother with partial thp at all and keep it in the original memcg > > > instead. It is way much less code and I do not think this will be too > > > disruptive. Somebody should be holding the thp head, right? > > > > > > Minchan, does this fix the issue you are seeing. > > > > This patch solves the issue but not sure it's right approach. > > I think it could make regression that in old, we could charge > > a THP page but we can't now. > > The page would still get charged when allocated. It just wouldn't get > moved when mapped only partially. IIUC there will be still somebody > mapping the THP head via pmd, right? That process will move the page to If I read code correctly, No. The split_huge_pmd splits just pmd, not page itself. IOW, it could be possible !pmd_trans_huge(pmd) && PageTransHuge although there is only process owns the page. > the new memcg when moved. Or is it possible that we will end up only > with pte mapped THP from all processes? Kirill? I'm not Kirill but I think it's possible. If so, a thing we can use is page_mapcount(page) == 1. With that, it could gaurantee only a process owns the page so charge 512 instead of 1? > > If not then I think it is reasonable to expect that partially mapped THP > is not moved during task migration. I will post an official patch after > Kirill confirms my understanding. > > Anyway thanks for the testing and pointing me to right direction > Minchan! Thanks for the quick patch and feedback, Michal. > > -- > Michal Hocko > SUSE Labs -- Kind regards, Minchan Kim -- 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>