From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198])
	by kanga.kvack.org (Postfix) with ESMTP id 4CFD76B025F
	for <linux-mm@kvack.org>; Tue, 25 Jul 2017 10:31:31 -0400 (EDT)
Received: by mail-pf0-f198.google.com with SMTP id h29so158579234pfd.2
        for <linux-mm@kvack.org>; Tue, 25 Jul 2017 07:31:31 -0700 (PDT)
Received: from mail-pg0-x243.google.com (mail-pg0-x243.google.com. [2607:f8b0:400e:c05::243])
        by mx.google.com with ESMTPS id p129si8143549pfp.193.2017.07.25.07.31.30
        for <linux-mm@kvack.org>
        (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
        Tue, 25 Jul 2017 07:31:30 -0700 (PDT)
Received: by mail-pg0-x243.google.com with SMTP id v190so14659526pgv.1
        for <linux-mm@kvack.org>; Tue, 25 Jul 2017 07:31:30 -0700 (PDT)
Date: Tue, 25 Jul 2017 17:31:20 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH v5 1/5] mm: add vm_insert_mixed_mkwrite()
Message-ID: <20170725143120.fyjcxwsoff34vqoj@node.shutemov.name>
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>
 <20170725125037.GH19943@quack2.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170725125037.GH19943@quack2.suse.cz>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>, Ross Zwisler <ross.zwisler@linux.intel.com>, Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, "Darrick J. Wong" <darrick.wong@oracle.com>, Theodore Ts'o <tytso@mit.edu>, Alexander Viro <viro@zeniv.linux.org.uk>, Andreas Dilger <adilger.kernel@dilger.ca>, Dan Williams <dan.j.williams@intel.com>, Dave Chinner <david@fromorbit.com>, Ingo Molnar <mingo@redhat.com>, Jonathan Corbet <corbet@lwn.net>, Matthew Wilcox <mawilcox@microsoft.com>, Steven Rostedt <rostedt@goodmis.org>, 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, Jul 25, 2017 at 02:50:37PM +0200, Jan Kara wrote:
> 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.

Yes. I was confused on how COW is handled.

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov

--
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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>