On Thu 02-08-12 14:33:10, Mel Gorman wrote: > On Thu, Aug 02, 2012 at 02:36:58PM +0200, Michal Hocko wrote: > > On Thu 02-08-12 08:37:57, Mel Gorman wrote: > > > On Thu, Aug 02, 2012 at 09:19:34AM +0200, Michal Hocko wrote: > > [...] > > > > On the other hand, mine is more coupled with the sharing code so it > > > > makes the code easier to follow and also makes the sharing more > > > > effective because racing processes see pmd populated when checking for > > > > shareable mappings. > > > > > > > > > > It could do with a small comment above huge_pmd_share() explaining that > > > calling pmd_alloc() under the i_mmap_mutex is necessary to prevent two > > > parallel faults missing a sharing opportunity with each other but it's > > > not mandatory. > > > > Sure, that's a good idea. What about the following: > > > > diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c > > index 40b2500..51839d1 100644 > > --- a/arch/x86/mm/hugetlbpage.c > > +++ b/arch/x86/mm/hugetlbpage.c > > @@ -56,7 +56,13 @@ static int vma_shareable(struct vm_area_struct *vma, unsigned long addr) > > } > > > > /* > > - * search for a shareable pmd page for hugetlb. > > + * search for a shareable pmd page for hugetlb. In any case calls > > + * pmd_alloc and returns the corresponding pte. While this not necessary > > + * for the !shared pmd case because we can allocate the pmd later as > > + * well it makes the code much cleaner. pmd allocation is essential for > > + * the shared case though because pud has to be populated inside the > > + * same i_mmap_mutex section otherwise racing tasks could either miss > > + * the sharing (see huge_pte_offset) or selected a bad pmd for sharing. > > */ > > static pte_t* > > huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) > > > > Looks reasonable to me. OK, added to the patch. I will send it to Andrew now. Thanks a lot! -- 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>