From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932205AbdBHOIj (ORCPT ); Wed, 8 Feb 2017 09:08:39 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40016 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753915AbdBHOIh (ORCPT ); Wed, 8 Feb 2017 09:08:37 -0500 Date: Wed, 8 Feb 2017 14:45:18 +0100 From: Andrea Arcangeli To: "Kirill A. Shutemov" Cc: Andrew Morton , "Kirill A. Shutemov" , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mprotect: drop overprotective lock_pte_protection() Message-ID: <20170208134518.GM25530@redhat.com> References: <20170207143347.123871-1-kirill.shutemov@linux.intel.com> <20170207134454.7af755ae379ca9d016b5c15a@linux-foundation.org> <20170208120421.GE5578@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170208120421.GE5578@node.shutemov.name> User-Agent: Mutt/1.7.2 (2016-11-26) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Wed, 08 Feb 2017 13:45:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 08, 2017 at 03:04:21PM +0300, Kirill A. Shutemov wrote: > On Tue, Feb 07, 2017 at 01:44:54PM -0800, Andrew Morton wrote: > > On Tue, 7 Feb 2017 17:33:47 +0300 "Kirill A. Shutemov" wrote: > > > > > lock_pte_protection() uses pmd_lock() to make sure that we have stable > > > PTE page table before walking pte range. > > > > > > That's not necessary. We only need to make sure that PTE page table is > > > established. It cannot vanish under us as long as we hold mmap_sem at > > > least for read. > > > > > > And we already have helper for that -- pmd_trans_unstable(). > > > > http://ozlabs.org/~akpm/mmots/broken-out/mm-mprotect-use-pmd_trans_unstable-instead-of-taking-the-pmd_lock.patch > > already did this? > > Right. Except, it doesn't drop unneeded pmd_trans_unstable(pmd) check after > __split_huge_pmd(). > > Could you fold this part of my patch into Andrea's? Reviewed-by: Andrea Arcangeli > > diff --git a/mm/mprotect.c b/mm/mprotect.c > index f9c07f54dd62..e919e4613eab 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -177,8 +149,6 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma, > if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) { > if (next - addr != HPAGE_PMD_SIZE) { > __split_huge_pmd(vma, pmd, addr, false, NULL); > - if (pmd_trans_unstable(pmd)) > - continue; > } else { > int nr_ptes = change_huge_pmd(vma, pmd, addr, > newprot, prot_numa); Yes this check was an harmless noop, but it's definitely good to clean up this bit too after the other more important change that has a positive runtime effect, or it could be a source of confusion to the reader if left in there. Thanks! Andrea