From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx175.postini.com [74.125.245.175]) by kanga.kvack.org (Postfix) with SMTP id 029A46B004D for ; Thu, 2 Aug 2012 09:53:53 -0400 (EDT) Date: Thu, 2 Aug 2012 15:53:50 +0200 From: Michal Hocko Subject: Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend) Message-ID: <20120802135350.GA18084@dhcp22.suse.cz> References: <50181AA1.0@redhat.com> <20120731200650.GB19524@tiehlicka.suse.cz> <50189857.4000501@redhat.com> <20120801082036.GC4436@tiehlicka.suse.cz> <20120801123209.GK4436@tiehlicka.suse.cz> <501945F9.2030402@redhat.com> <20120802071934.GA7557@dhcp22.suse.cz> <20120802073757.GC29814@suse.de> <20120802123658.GA5194@dhcp22.suse.cz> <20120802133310.GD29814@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120802133310.GD29814@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Larry Woodman , Rik van Riel , Hugh Dickins , Linux-MM , David Gibson , Ken Chen , Cong Wang , LKML 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@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org