From: Dan Williams <dan.j.williams@intel.com>
To: Jane Chu <jane.chu@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>,
"Darrick J. Wong" <djwong@kernel.org>,
"david@fromorbit.com" <david@fromorbit.com>,
"vishal.l.verma@intel.com" <vishal.l.verma@intel.com>,
"dave.jiang@intel.com" <dave.jiang@intel.com>,
"agk@redhat.com" <agk@redhat.com>,
"snitzer@redhat.com" <snitzer@redhat.com>,
"dm-devel@redhat.com" <dm-devel@redhat.com>,
"ira.weiny@intel.com" <ira.weiny@intel.com>,
"willy@infradead.org" <willy@infradead.org>,
"vgoyal@redhat.com" <vgoyal@redhat.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"nvdimm@lists.linux.dev" <nvdimm@lists.linux.dev>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>
Subject: Re: [dm-devel] [PATCH 0/6] dax poison recovery with RWF_RECOVERY_DATA flag
Date: Thu, 4 Nov 2021 12:00:12 -0700 [thread overview]
Message-ID: <CAPcyv4hJjcy2TnOv-Y5=MUMHeDdN-BCH4d0xC-pFGcHXEU_ZEw@mail.gmail.com> (raw)
In-Reply-To: <6d21ece1-0201-54f2-ec5a-ae2f873d46a3@oracle.com>
On Thu, Nov 4, 2021 at 11:34 AM Jane Chu <jane.chu@oracle.com> wrote:
>
> Thanks for the enlightening discussion here, it's so helpful!
>
> Please allow me to recap what I've caught up so far -
>
> 1. recovery write at page boundary due to NP setting in poisoned
> page to prevent undesirable prefetching
> 2. single interface to perform 3 tasks:
> { clear-poison, update error-list, write }
> such as an API in pmem driver.
> For CPUs that support MOVEDIR64B, the 'clear-poison' and 'write'
> task can be combined (would need something different from the
> existing _copy_mcsafe though) and 'update error-list' follows
> closely behind;
> For CPUs that rely on firmware call to clear posion, the existing
> pmem_clear_poison() can be used, followed by the 'write' task.
> 3. if user isn't given RWF_RECOVERY_FLAG flag, then dax recovery
> would be automatic for a write if range is page aligned;
> otherwise, the write fails with EIO as usual.
> Also, user mustn't have punched out the poisoned page in which
> case poison repairing will be a lot more complicated.
> 4. desirable to fetch as much data as possible from a poisoned range.
>
> If this understanding is in the right direction, then I'd like to
> propose below changes to
> dax_direct_access(), dax_copy_to/from_iter(), pmem_copy_to/from_iter()
> and the dm layer copy_to/from_iter, dax_iomap_iter().
>
> 1. dax_iomap_iter() rely on dax_direct_access() to decide whether there
> is likely media error: if the API without DAX_F_RECOVERY returns
> -EIO, then switch to recovery-read/write code. In recovery code,
> supply DAX_F_RECOVERY to dax_direct_access() in order to obtain
> 'kaddr', and then call dax_copy_to/from_iter() with DAX_F_RECOVERY.
I like it. It allows for an atomic write+clear implementation on
capable platforms and coordinates with potentially unmapped pages. The
best of both worlds from the dax_clear_poison() proposal and my "take
a fault and do a slow-path copy".
> 2. the _copy_to/from_iter implementation would be largely the same
> as in my recent patch, but some changes in Christoph's
> 'dax-devirtualize' maybe kept, such as DAX_F_VIRTUAL, obviously
> virtual devices don't have the ability to clear poison, so no need
> to complicate them. And this also means that not every endpoint
> dax device has to provide dax_op.copy_to/from_iter, they may use the
> default.
Did I miss this series or are you talking about this one?
https://lore.kernel.org/all/20211018044054.1779424-1-hch@lst.de/
> I'm not sure about nova and others, if they use different 'write' other
> than via iomap, does that mean there will be need for a new set of
> dax_op for their read/write?
No, they're out-of-tree they'll adjust to the same interface that xfs
and ext4 are using when/if they go upstream.
> the 3-in-1 binding would always be
> required though. Maybe that'll be an ongoing discussion?
Yeah, let's cross that bridge when we come to it.
> Comments? Suggestions?
It sounds great to me!
next prev parent reply other threads:[~2021-11-04 19:00 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-21 0:10 [PATCH 0/6] dax poison recovery with RWF_RECOVERY_DATA flag Jane Chu
2021-10-21 0:10 ` [PATCH 1/6] dax: introduce RWF_RECOVERY_DATA flag to preadv2() and pwritev2() Jane Chu
2021-10-21 0:10 ` [PATCH 2/6] dax: prepare dax_direct_access() API with DAXDEV_F_RECOVERY flag Jane Chu
2021-10-21 11:20 ` Christoph Hellwig
2021-10-21 18:19 ` Jane Chu
2021-10-21 0:10 ` [PATCH 3/6] pmem: pmem_dax_direct_access() to honor the " Jane Chu
2021-10-21 11:23 ` Christoph Hellwig
2021-10-21 18:24 ` Jane Chu
2021-10-21 0:10 ` [PATCH 4/6] dm,dax,pmem: prepare dax_copy_to/from_iter() APIs with DAXDEV_F_RECOVERY Jane Chu
2021-10-21 11:27 ` Christoph Hellwig
2021-10-22 0:49 ` Jane Chu
2021-10-22 1:41 ` correction: " Jane Chu
2021-10-22 5:33 ` Christoph Hellwig
2021-10-22 20:30 ` Jane Chu
2021-10-21 0:10 ` [PATCH 5/6] dax,pmem: Add data recovery feature to pmem_copy_to/from_iter() Jane Chu
2021-10-21 11:28 ` Christoph Hellwig
2021-10-22 0:58 ` Jane Chu
2021-10-21 0:10 ` [PATCH 6/6] dm: Ensure dm honors DAXDEV_F_RECOVERY flag on dax only Jane Chu
2021-10-21 11:31 ` [dm-devel] [PATCH 0/6] dax poison recovery with RWF_RECOVERY_DATA flag Christoph Hellwig
2021-10-22 1:37 ` Jane Chu
2021-10-22 1:58 ` Darrick J. Wong
2021-10-22 5:38 ` Christoph Hellwig
2021-10-22 5:36 ` Christoph Hellwig
2021-10-22 20:52 ` Jane Chu
2021-10-27 6:49 ` Christoph Hellwig
2021-10-28 0:24 ` Darrick J. Wong
2021-10-28 22:59 ` Dave Chinner
2021-10-29 11:46 ` Pavel Begunkov
2021-10-29 16:57 ` Darrick J. Wong
2021-10-29 19:23 ` Pavel Begunkov
2021-10-29 20:08 ` Darrick J. Wong
2021-10-31 13:27 ` Pavel Begunkov
2021-10-29 18:53 ` Jane Chu
2021-10-29 22:32 ` Dave Chinner
2021-10-31 13:19 ` Pavel Begunkov
2021-11-01 2:31 ` Matthew Wilcox
2021-11-02 6:18 ` Christoph Hellwig
2021-11-02 19:57 ` Dan Williams
2021-11-03 16:58 ` Christoph Hellwig
2021-11-03 20:33 ` Dan Williams
2021-11-04 8:30 ` Christoph Hellwig
2021-11-04 12:29 ` Matthew Wilcox
2021-11-04 16:24 ` Dan Williams
2021-11-04 17:43 ` Christoph Hellwig
2021-11-04 17:50 ` Dan Williams
2021-11-04 18:05 ` Matthew Wilcox
2021-11-04 18:33 ` Jane Chu
2021-11-04 19:00 ` Dan Williams [this message]
2021-11-04 20:27 ` Jane Chu
2021-11-05 0:46 ` Dan Williams
2021-11-05 1:35 ` Dan Williams
2021-11-05 5:56 ` Christoph Hellwig
2021-11-03 18:09 ` Jane Chu
2021-11-04 6:21 ` Dan Williams
2021-11-04 8:36 ` Christoph Hellwig
2021-11-04 16:08 ` Dan Williams
2021-11-04 17:46 ` Christoph Hellwig
2021-11-04 8:21 ` Christoph Hellwig
2021-11-02 16:12 ` Dan Williams
2021-11-02 16:03 ` Dan Williams
2021-11-03 16:53 ` Christoph Hellwig
2021-11-06 7:41 ` Lukas Straub
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