From: Ruan Shiyang <ruansy.fnst@cn.fujitsu.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Matthew Wilcox <willy@infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"darrick.wong@oracle.com" <darrick.wong@oracle.com>,
"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
"hch@lst.de" <hch@lst.de>, "rgoldwyn@suse.de" <rgoldwyn@suse.de>,
"Qi, Fuli" <qi.fuli@fujitsu.com>,
"Gotou, Yasunori" <y-goto@fujitsu.com>
Subject: Re: 回复: Re: [RFC PATCH 0/8] dax: Add a dax-rmap tree to support reflink
Date: Thu, 4 Jun 2020 15:37:42 +0800 [thread overview]
Message-ID: <153e13e6-8685-fb0d-6bd3-bb553c06bf51@cn.fujitsu.com> (raw)
In-Reply-To: <20200428064318.GG2040@dread.disaster.area>
On 2020/4/28 下午2:43, Dave Chinner wrote:
> On Tue, Apr 28, 2020 at 06:09:47AM +0000, Ruan, Shiyang wrote:
>>
>> 在 2020/4/27 20:28:36, "Matthew Wilcox" <willy@infradead.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...
>
> That's why I want the -user of this association- to do a filesystem
> callout instead of keeping it's own naive tracking infrastructure.
> The filesystem can do an efficient, on-demand reverse mapping lookup
> from it's own extent tracking infrastructure, and there's zero
> runtime overhead when there are no errors present.
Hi Dave,
I ran into some difficulties when trying to implement the per-extent
rmap tracking. So, I re-read your comments and found that I was
misunderstanding what you described here.
I think what you mean is: we don't need the in-memory dax-rmap tracking
now. Just ask the FS for the owner's information that associate with
one page when memory-failure. So, the per-page (even per-extent)
dax-rmap is needless in this case. Is this right?
Based on this, we only need to store the extent information of a fsdax
page in its ->mapping (by searching from FS). Then obtain the owners of
this page (also by searching from FS) when memory-failure or other rmap
case occurs.
So, a fsdax page is no longer associated with a specific file, but with
a FS(or the pmem device). I think it's easier to understand and implement.
--
Thanks,
Ruan Shiyang.
>
> At the moment, this "dax association" is used to "report" a storage
> media error directly to userspace. I say "report" because what it
> does is kill userspace processes dead. The storage media error
> actually needs to be reported to the owner of the storage media,
> which in the case of FS-DAX is the filesytem.
>
> That way the filesystem can then look up all the owners of that bad
> media range (i.e. the filesystem block it corresponds to) and take
> appropriate action. e.g.
>
> - if it falls in filesytem metadata, shutdown the filesystem
> - if it falls in user data, call the "kill userspace dead" routines
> for each mapping/index tuple the filesystem finds for the given
> LBA address that the media error occurred.
>
> Right now if the media error is in filesystem metadata, the
> filesystem isn't even told about it. The filesystem can't even shut
> down - the error is just dropped on the floor and it won't be until
> the filesystem next tries to reference that metadata that we notice
> there is an issue.
>
> Cheers,
>
> Dave.
>
next prev parent reply other threads:[~2020-06-04 7:38 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-27 8:47 [RFC PATCH 0/8] dax: Add a dax-rmap tree to support reflink Shiyang Ruan
2020-04-27 8:47 ` [RFC PATCH 1/8] fs/dax: Introduce dax-rmap btree for reflink Shiyang Ruan
2020-04-27 8:47 ` [RFC PATCH 2/8] mm: add dax-rmap for memory-failure and rmap Shiyang Ruan
2020-04-27 8:47 ` [RFC PATCH 3/8] fs/dax: Introduce dax_copy_edges() for COW Shiyang Ruan
2020-04-27 8:47 ` [RFC PATCH 4/8] fs/dax: copy data before write Shiyang Ruan
2020-04-27 8:47 ` [RFC PATCH 5/8] fs/dax: replace mmap entry in case of CoW Shiyang Ruan
2020-04-27 8:47 ` [RFC PATCH 6/8] fs/dax: dedup file range to use a compare function Shiyang Ruan
2020-04-27 8:47 ` [RFC PATCH 7/8] fs/xfs: handle CoW for fsdax write() path Shiyang Ruan
2020-04-27 8:47 ` [RFC PATCH 8/8] fs/xfs: support dedupe for fsdax Shiyang Ruan
2020-04-27 12:28 ` [RFC PATCH 0/8] dax: Add a dax-rmap tree to support reflink Matthew Wilcox
2020-04-28 6:09 ` 回复: " Ruan, Shiyang
2020-04-28 6:43 ` Dave Chinner
2020-04-28 9:32 ` Ruan Shiyang
2020-04-28 11:16 ` Matthew Wilcox
2020-04-28 11:24 ` Dave Chinner
2020-04-28 15:37 ` Darrick J. Wong
2020-04-28 22:02 ` Dave Chinner
2020-06-04 7:37 ` Ruan Shiyang [this message]
2020-06-04 14:51 ` Darrick J. Wong
2020-06-05 1:30 ` Dave Chinner
2020-06-05 2:30 ` Ruan Shiyang
2020-06-05 2:11 ` Ruan Shiyang
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