From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Ruan Shiyang <ruansy.fnst@cn.fujitsu.com>
Cc: Dave Chinner <david@fromorbit.com>,
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>,
"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 07:51:07 -0700 [thread overview]
Message-ID: <20200604145107.GA1334206@magnolia> (raw)
In-Reply-To: <153e13e6-8685-fb0d-6bd3-bb553c06bf51@cn.fujitsu.com>
On Thu, Jun 04, 2020 at 03:37:42PM +0800, Ruan Shiyang wrote:
>
>
> 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?
Right. XFS already has its own rmap tree.
> 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.
I don't even think you need that much. All you need is the "physical"
offset of that page within the pmem device (e.g. 'this is the 307th 4k
page == offset 1257472 since the start of /dev/pmem0') and xfs can look
up the owner of that range of physical storage and deal with it as
needed.
> 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.
Yes. I also suspect this will be necessary to support reflink...
--D
>
> --
> 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 14:51 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
2020-06-04 14:51 ` Darrick J. Wong [this message]
2020-06-05 1:30 ` Dave Chinner
2020-06-05 2:30 ` Ruan Shiyang
2020-06-05 2:11 ` Ruan Shiyang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200604145107.GA1334206@magnolia \
--to=darrick.wong@oracle.com \
--cc=dan.j.williams@intel.com \
--cc=david@fromorbit.com \
--cc=hch@lst.de \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-nvdimm@lists.01.org \
--cc=linux-xfs@vger.kernel.org \
--cc=qi.fuli@fujitsu.com \
--cc=rgoldwyn@suse.de \
--cc=ruansy.fnst@cn.fujitsu.com \
--cc=willy@infradead.org \
--cc=y-goto@fujitsu.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).