From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx166.postini.com [74.125.245.166]) by kanga.kvack.org (Postfix) with SMTP id 68E076B0027 for ; Wed, 20 Mar 2013 03:41:22 -0400 (EDT) Date: Wed, 20 Mar 2013 08:41:18 +0100 From: Michal Hocko Subject: Re: [PATCH 5/9] migrate: enable migrate_pages() to migrate hugepage Message-ID: <20130320074118.GB20045@dhcp22.suse.cz> References: <1361475708-25991-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1361475708-25991-6-git-send-email-n-horiguchi@ah.jp.nec.com> <20130318154057.GS10192@dhcp22.suse.cz> <1363651636-3lsf20se-mutt-n-horiguchi@ah.jp.nec.com> <20130319071113.GD5112@dhcp22.suse.cz> <1363759974-38t0k25g-mutt-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1363759974-38t0k25g-mutt-n-horiguchi@ah.jp.nec.com> Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: linux-mm@kvack.org, Andrew Morton , Mel Gorman , Hugh Dickins , KOSAKI Motohiro , Andi Kleen , linux-kernel@vger.kernel.org On Wed 20-03-13 02:12:54, Naoya Horiguchi wrote: > On Tue, Mar 19, 2013 at 08:11:13AM +0100, Michal Hocko wrote: > > On Mon 18-03-13 20:07:16, Naoya Horiguchi wrote: > > > On Mon, Mar 18, 2013 at 04:40:57PM +0100, Michal Hocko wrote: > > > > On Thu 21-02-13 14:41:44, Naoya Horiguchi wrote: > ... > > > > > @@ -536,6 +557,11 @@ static inline int check_pmd_range(struct vm_area_struct *vma, pud_t *pud, > > > > > pmd = pmd_offset(pud, addr); > > > > > do { > > > > > next = pmd_addr_end(addr, end); > > > > > + if (pmd_huge(*pmd) && is_vm_hugetlb_page(vma)) { > > > > > > > > Why an explicit check for is_vm_hugetlb_page here? Isn't pmd_huge() > > > > sufficient? > > > > > > I think we need both check here because if we use only pmd_huge(), > > > pmd for thp goes into this branch wrongly. > > > > Bahh. You are right. I thought that pmd_huge is hugetlb thingy but it > > obviously checks only _PAGE_PSE same as pmd_large() which is really > > unfortunate and confusing. Can we make it hugetlb specific? > > I agree that we had better fix this confusion. > > What pmd_huge() (or pmd_large() in some architectures) does is just > checking whether a given pmd is pointing to huge/large page or not. > It does not say which type of hugepage it is. > So it shouldn't be used to decide whether the hugepage are hugetlbfs or not. > I think it would be better to introduce pmd_hugetlb() which has pmd and vma > as arguments and returns true only for hugetlbfs pmd. > Checking pmd_hugetlb() should come before checking pmd_trans_huge() because > pmd_trans_huge() implicitly assumes that the vma which covers the virtual > address of a given pmd is not hugetlbfs vma. > > I'm interested in this cleanup, so will work on it after this patchset. pnd_huge is used only at few places so it shouldn't be very big. On the other hand you do not have vma always available so it is getting tricky. Thanks -- 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