From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754280AbcJKSoe (ORCPT ); Tue, 11 Oct 2016 14:44:34 -0400 Received: from mx2.suse.de ([195.135.220.15]:42815 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753427AbcJKSnj (ORCPT ); Tue, 11 Oct 2016 14:43:39 -0400 Date: Tue, 11 Oct 2016 17:47:50 +0200 From: Jan Kara To: "Kirill A. Shutemov" Cc: "Theodore Ts'o" , Andreas Dilger , Jan Kara , Andrew Morton , Alexander Viro , Hugh Dickins , Andrea Arcangeli , Dave Hansen , Vlastimil Babka , Matthew Wilcox , Ross Zwisler , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org Subject: Re: [PATCHv3 12/41] thp: handle write-protection faults for file THP Message-ID: <20161011154750.GL6952@quack2.suse.cz> References: <20160915115523.29737-1-kirill.shutemov@linux.intel.com> <20160915115523.29737-13-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160915115523.29737-13-kirill.shutemov@linux.intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 15-09-16 14:54:54, Kirill A. Shutemov wrote: > For filesystems that wants to be write-notified (has mkwrite), we will > encount write-protection faults for huge PMDs in shared mappings. > > The easiest way to handle them is to clear the PMD and let it refault as > wriable. > > Signed-off-by: Kirill A. Shutemov > --- > mm/memory.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 83be99d9d8a1..aad8d5c6311f 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3451,8 +3451,17 @@ static int wp_huge_pmd(struct fault_env *fe, pmd_t orig_pmd) > return fe->vma->vm_ops->pmd_fault(fe->vma, fe->address, fe->pmd, > fe->flags); > > + if (fe->vma->vm_flags & VM_SHARED) { > + /* Clear PMD */ > + zap_page_range_single(fe->vma, fe->address, > + HPAGE_PMD_SIZE, NULL); > + VM_BUG_ON(!pmd_none(*fe->pmd)); > + > + /* Refault to establish writable PMD */ > + return 0; > + } > + Since we want to write-protect the page table entry on each page writeback and write-enable then on the next write, this is relatively expensive. Would it be that complicated to handle this fully in ->pmd_fault handler like we do for DAX? Maybe it doesn't have to be done now but longer term I guess it might make sense. Otherwise the patch looks good so feel free to add: Reviewed-by: Jan Kara Honza -- Jan Kara SUSE Labs, CR