linux-kernel - Re: [RFC PATCH v2 0/7] xfs: reflink & dedupe for fsdax (read/write path).

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Message-ID: <2737c6f6-5cca-2b92-edff-fb9227ccc6d1@cn.fujitsu.com>
Date:   Thu, 31 Oct 2019 12:54:54 +0800
From:   Shiyang Ruan <ruansy.fnst@...fujitsu.com>
To:     Goldwyn Rodrigues <rgoldwyn@...e.de>
CC:     <linux-xfs@...r.kernel.org>, <linux-nvdimm@...ts.01.org>,
        <darrick.wong@...cle.com>, <hch@...radead.org>,
        <david@...morbit.com>, <linux-kernel@...r.kernel.org>,
        <gujx@...fujitsu.com>, <qi.fuli@...itsu.com>,
        <caoj.fnst@...fujitsu.com>
Subject: Re: [RFC PATCH v2 0/7] xfs: reflink & dedupe for fsdax (read/write
 path).



On 10/30/19 7:48 PM, Goldwyn Rodrigues wrote:
> On 12:13 30/10, Shiyang Ruan wrote:
>> This patchset aims to take care of this issue to make reflink and dedupe
>> work correctly (actually in read/write path, there still has some problems,
>> such as the page->mapping and page->index issue, in mmap path) in XFS under
>> fsdax mode.
> 
> Have you managed to solve the problem of multi-mapped pages? I don't
> think we can include this until we solve that problem. This is the
> problem I faced when I was doing the btrfs dax support.

That problem still exists, didn't be solved in this patchset.  But I am 
also looking into it.  As you know, it's a bit difficult.

Since the iomap for cow is merged in for-next tree, I think it's time to 
update this in order to get some comments.

> 
> Suppose there is an extent shared with multiple files. You map data for
> both files. Which inode should page->mapping->host (precisely
> page->mapping) point to? As Dave pointed out, this needs to be fixed at
> the mm level, and will not only benefit dax with CoW but other
> areas such as overlayfs and possibly containers.

Yes, I will try to figure out a solution.
> 

-- 
Thanks,
Shiyang Ruan.