linux-kernel - 回复: Re: [RFC PATCH 0/8] dax: Add a dax-rmap tree to support reflink

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Date:   Tue, 28 Apr 2020 06:09:47 +0000
From:   "Ruan, Shiyang" <ruansy.fnst@...fujitsu.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "darrick.wong@...cle.com" <darrick.wong@...cle.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "david@...morbit.com" <david@...morbit.com>,
        "hch@....de" <hch@....de>, "rgoldwyn@...e.de" <rgoldwyn@...e.de>,
        "Qi, Fuli" <qi.fuli@...itsu.com>,
        "Gotou, Yasunori" <y-goto@...itsu.com>
Subject: 回复: Re: [RFC PATCH 0/8] dax: Add a dax-rmap tree to support reflink


在 2020/4/27 20:28:36, "Matthew Wilcox" <willy@...radead.org> 写道:

>On Mon, Apr 27, 2020 at 04:47:42PM +0800, Shiyang Ruan wrote:
>>  This patchset is a try to resolve the shared 'page cache' problem for
>>  fsdax.
>>
>>  In order to track multiple mappings and indexes on one page, I
>>  introduced a dax-rmap rb-tree to manage the relationship.  A dax entry
>>  will be associated more than once if is shared.  At the second time we
>>  associate this entry, we create this rb-tree and store its root in
>>  page->private(not used in fsdax).  Insert (->mapping, ->index) when
>>  dax_associate_entry() and delete it when dax_disassociate_entry().
>
>Do we really want to track all of this on a per-page basis?  I would
>have thought a per-extent basis was more useful.  Essentially, create
>a new address_space for each shared extent.  Per page just seems like
>a huge overhead.
>
Per-extent tracking is a nice idea for me.  I haven't thought of it 
yet...

But the extent info is maintained by filesystem.  I think we need a way 
to obtain this info from FS when associating a page.  May be a bit 
complicated.  Let me think about it...


--
Thanks,
Ruan Shiyang.