> From: Steve Capper [mailto:steve.capper@xxxxxxx] > Sent: Wednesday, April 10, 2013 5:21 PM > To: Chanho Park > Cc: Steve Capper; 'Chanho Park'; linux@xxxxxxxxxxxxxxxx; Catalin Marinas; > 'Inki Dae'; linux-mm@xxxxxxxxx; 'Kyungmin Park'; 'Myungjoo Ham'; linux- > arm-kernel@xxxxxxxxxxxxxxxxxxx; 'Grazvydas Ignotas' > Subject: Re: [PATCH] arm: mm: lockless get_user_pages_fast > > On Wed, Apr 10, 2013 at 08:30:54AM +0100, Chanho Park wrote: > > > Apologies for the tardy response, this patch slipped past me. > > > > Never mind. > > > > > I've tested this patch out, unfortunately it treats huge pmds as > > > regular pmds and attempts to traverse them rather than fall back to a > slow path. > > > The fix for this is very minor, please see my suggestion below. > > OK. I'll fix it. > > > > > > > > As an aside, I would like to extend this fast_gup to include full > > > huge page support and include a __get_user_pages_fast > > > implementation. This will hopefully fix a problem that was brought > > > to my attention by Grazvydas Ignotas whereby a FUTEX_WAIT on a THP > > > tail page will cause an infinite loop due to the stock > > > implementation of __get_user_pages_fast always returning 0. > > > > I'll add the __get_user_pages_fast implementation. BTW, HugeTLB on ARM > > wasn't supported yet. There is no problem to add gup_huge_pmd. But I > > think it need a test for hugepages. > > > > Thanks, that would be helpful. My plan was to then put the huge page > specific bits in, with another patch. That way I can test it all out here. Can I see the patch? I think it will be helpful to implement the gup_huge_pmd. Or how about you think except gup_huge_pmd in this patch? IMO it will be added easily after hugetlb on arm is merged. > > > > I would suggest: > > > if (pmd_none(*pmdp) || pmd_bad(*pmdp)) > > > return 0; > > > as this will pick up pmds that can't be traversed, and fall back to > > > the slow path. > > > > Thanks for your suggestion. > > I'll prepare the v2 patch. > > > > Also, just one more thing. In your gup_pte_range function there is an > smp_rmb() just after the pte is dereferenced. I don't understand why > though? I think it would be needed for 64 bit machine. A pte of 64bit machine consists of low and high value. In this version, there is no need to add it. I'll remove it. Thanks. Best regards, Chanho Park -- 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>