From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f200.google.com (mail-wr0-f200.google.com [209.85.128.200]) by kanga.kvack.org (Postfix) with ESMTP id 63C0F6B025F for ; Tue, 25 Jul 2017 08:50:45 -0400 (EDT) Received: by mail-wr0-f200.google.com with SMTP id r7so28217696wrb.0 for ; Tue, 25 Jul 2017 05:50:45 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id u74si7353056wmf.54.2017.07.25.05.50.43 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 25 Jul 2017 05:50:44 -0700 (PDT) Date: Tue, 25 Jul 2017 14:50:37 +0200 From: Jan Kara Subject: Re: [PATCH v5 1/5] mm: add vm_insert_mixed_mkwrite() Message-ID: <20170725125037.GH19943@quack2.suse.cz> References: <20170724170616.25810-1-ross.zwisler@linux.intel.com> <20170724170616.25810-2-ross.zwisler@linux.intel.com> <20170724221400.pcq5zvke7w2yfkxi@node.shutemov.name> <20170725080158.GA5374@lst.de> <20170725093508.GA19943@quack2.suse.cz> <20170725121522.GA13457@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170725121522.GA13457@lst.de> Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Hellwig Cc: Jan Kara , "Kirill A. Shutemov" , Ross Zwisler , Andrew Morton , linux-kernel@vger.kernel.org, "Darrick J. Wong" , Theodore Ts'o , Alexander Viro , Andreas Dilger , Dan Williams , Dave Chinner , Ingo Molnar , Jonathan Corbet , Matthew Wilcox , Steven Rostedt , linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-xfs@vger.kernel.org On Tue 25-07-17 14:15:22, Christoph Hellwig wrote: > On Tue, Jul 25, 2017 at 11:35:08AM +0200, Jan Kara wrote: > > On Tue 25-07-17 10:01:58, Christoph Hellwig wrote: > > > On Tue, Jul 25, 2017 at 01:14:00AM +0300, Kirill A. Shutemov wrote: > > > > I guess it's up to filesystem if it wants to reuse the same spot to write > > > > data or not. I think your assumptions works for ext4 and xfs. I wouldn't > > > > be that sure for btrfs or other filesystems with CoW support. > > > > > > Or XFS with reflinks for that matter. Which currently can't be > > > combined with DAX, but I had a somewhat working version a few month > > > ago. > > > > But in cases like COW when the block mapping changes, the process > > must run unmap_mapping_range() before installing the new PTE so that all > > processes mapping this file offset actually refault and see the new > > mapping. So this would go through pte_none() case. Am I missing something? > > Yes, for DAX COW mappings we'd probably need something like this, unlike > the pagecache COW handling for which only the underlying block change, > but not the page. Right. So again nothing where the WARN_ON should trigger. That being said I don't care about the WARN_ON too deeply but it can help to catch DAX bugs so if we can keep it I'd prefer to do so... Honza -- Jan Kara SUSE Labs, CR -- 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