linux-kernel - Re: [RFC PATCH 0/8] fsdax: introduce FS query interface to support reflink

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Message-ID: <9673ed3c-9e42-3d01-000b-b01cda9832ce@cn.fujitsu.com>
Date:   Mon, 10 Aug 2020 16:15:50 +0800
From:   Ruan Shiyang <ruansy.fnst@...fujitsu.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-xfs@...r.kernel.org>,
        <linux-nvdimm@...ts.01.org>, <linux-mm@...ck.org>,
        <linux-fsdevel@...r.kernel.org>, <darrick.wong@...cle.com>,
        <dan.j.williams@...el.com>, <david@...morbit.com>, <hch@....de>,
        <rgoldwyn@...e.de>, <qi.fuli@...itsu.com>, <y-goto@...itsu.com>
Subject: Re: [RFC PATCH 0/8] fsdax: introduce FS query interface to support
 reflink



On 2020/8/7 下午9:38, Matthew Wilcox wrote:
> On Fri, Aug 07, 2020 at 09:13:28PM +0800, Shiyang Ruan wrote:
>> This patchset is a try to resolve the problem of tracking shared page
>> for fsdax.
>>
>> Instead of per-page tracking method, this patchset introduces a query
>> interface: get_shared_files(), which is implemented by each FS, to
>> obtain the owners of a shared page.  It returns an owner list of this
>> shared page.  Then, the memory-failure() iterates the list to be able
>> to notify each process using files that sharing this page.
>>
>> The design of the tracking method is as follow:
>> 1. dax_assocaite_entry() associates the owner's info to this page
> 
> I think that's the first problem with this design.  dax_associate_entry is
> a horrendous idea which needs to be ripped out, not made more important.
> It's all part of the general problem of trying to do something on a
> per-page basis instead of per-extent basis.
> 

The memory-failure needs to track owners info from a dax page, so I 
should associate the owner with this page.  In this version, I associate 
the block device to the dax page, so that the memory-failure is able to 
iterate the owners by the query interface provided by filesystem.


--
Thanks,
Ruan Shiyang.
> 
>