On Fri 20-07-12 15:37:53, Mel Gorman wrote: > On Fri, Jul 20, 2012 at 04:29:20PM +0200, Michal Hocko wrote: > > > <SNIP> > > > > > > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > > > > Yes this looks correct. mmap_sem will make sure that unmap_vmas and > > free_pgtables are executed atomicaly wrt. huge_pmd_share so it doesn't > > see non-NULL spte on the way out. > > Yes. > > > I am just wondering whether we need > > the page_table_lock as well. It is not harmful but I guess we can drop > > it because both exit_mmap and shmdt are not taking it and mmap_sem is > > sufficient for them. > > While it is true that we don't *really* need page_table_lock here, we are > still updating page tables and it's in line with the the ordinary locking > rules. There are other cases in hugetlb.c where we do pte_same() checks even > though we are protected from the related races by the instantiation_mutex. > > page_table_lock is actually a bit useless for shared page tables. If shared > page tables were every to be a general thing then I think we'd have to > revisit how PTE update locking is done but I doubt anyone wants to dive > down that rat-hole. > > For now, I'm going to keep taking it even if strictly speaking it's not > necessary. Fair enough -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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>