From: Christoph Hellwig <hch@infradead.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@infradead.org>,
"Darrick J. Wong" <djwong@kernel.org>,
Jane Chu <jane.chu@oracle.com>,
"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: Wed, 3 Nov 2021 09:58:28 -0700 [thread overview]
Message-ID: <YYK/tGfpG0CnVIO4@infradead.org> (raw)
In-Reply-To: <CAPcyv4j8snuGpy=z6BAXogQkP5HmTbqzd6e22qyERoNBvFKROw@mail.gmail.com>
On Tue, Nov 02, 2021 at 12:57:10PM -0700, Dan Williams wrote:
> This goes back to one of the original DAX concerns of wanting a kernel
> library for coordinating PMEM mmap I/O vs leaving userspace to wrap
> PMEM semantics on top of a DAX mapping. The problem is that mmap-I/O
> has this error-handling-API issue whether it is a DAX mapping or not.
Semantics of writes through shared mmaps are a nightmare. Agreed,
including agreeing that this is neither new nor pmem specific. But
it also has absolutely nothing to do with the new RWF_ flag.
> CONFIG_ARCH_SUPPORTS_MEMORY_FAILURE implies that processes will
> receive SIGBUS + BUS_MCEERR_A{R,O} when memory failure is signalled
> and then rely on readv(2)/writev(2) to recover. Do you see a readily
> available way to improve upon that model without CPU instruction
> changes? Even with CPU instructions changes, do you think it could
> improve much upon the model of interrupting the process when a load
> instruction aborts?
The "only" think we need is something like the exception table we
use in the kernel for the uaccess helpers (and the new _nofault
kernel access helper). But I suspect refitting that into userspace
environments is probably non-trivial.
> I do agree with you that DAX needs to separate itself from block, but
> I don't think it follows that DAX also needs to separate itself from
> readv/writev for when a kernel slow-path needs to get involved because
> mmap I/O (just CPU instructions) does not have the proper semantics.
> Even if you got one of the ARCH_SUPPORTS_MEMORY_FAILURE to implement
> those semantics in new / augmented CPU instructions you will likely
> not get all of them to move and certainly not in any near term
> timeframe, so the kernel path will be around indefinitely.
I think you misunderstood me. I don't think pmem needs to be
decoupled from the read/write path. But I'm very skeptical of adding
a new flag to the common read/write path for the special workaround
that a plain old write will not actually clear errors unlike every
other store interfac.
> Meanwhile, I think RWF_RECOVER_DATA is generically useful for other
> storage besides PMEM and helps storage-drivers do better than large
> blast radius "I/O error" completions with no other recourse.
How?
next prev parent reply other threads:[~2021-11-03 16:58 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 [this message]
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
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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