From: Christoph Hellwig <hch@infradead.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: [PATCH] dax: adding fsync/msync support for device DAX
Date: Thu, 5 Apr 2018 00:23:17 -0700 [thread overview]
Message-ID: <20180405072317.GA2855@infradead.org> (raw)
In-Reply-To: <CAPcyv4hZfNOG15guKE0Lq=QoFr8DZerEH=1=OjnrEY2trPXNcw@mail.gmail.com>
On Wed, Apr 04, 2018 at 05:03:07PM -0700, Dan Williams wrote:
> "Currently, fsdax applications can assume that if they call fsync or
> msync on a dax mapped file that any pending writes that have been
> flushed out of the cpu cache will be also be flushed to the lowest
> possible persistence / failure domain available on the platform. In
> typical scenarios the platform ADR capability handles marshaling
> writes that have reached global visibility to persistence. In
> exceptional cases where ADR fails to complete its operation software
> can detect that scenario the the "last shutdown" health status check
> and otherwise mitigate the effects of an ADR failure by protecting
> metadata with the WPQ flush. In other words, enabling device-dax to
> optionally trigger WPQ Flush on msync() allows applications to have
> common implementation for persistence domain handling across fs-dax
> and device-dax."
This sounds totally bogus. Either ADR is reliable and we can rely on
it all the time (like we assume for say capacitors on ssds with non-
volatile write caches), or we can't rely on it and the write through
store model is a blatant lie. In other words - msync/fsync is what
we use for normal persistence, not for working around broken hardware.
In many ways this sounds like a plot to make normal programming models
not listening to the pmem.io hype look bad in benchmarks..
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next prev parent reply other threads:[~2018-04-05 7:23 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-04 22:01 [PATCH] dax: adding fsync/msync support for device DAX Dave Jiang
2018-04-05 0:03 ` Dan Williams
2018-04-05 7:23 ` Christoph Hellwig [this message]
2018-04-05 7:56 ` Dan Williams
2018-04-05 8:01 ` Christoph Hellwig
2018-04-05 14:59 ` Jeff Moyer
2018-04-05 15:10 ` Christoph Hellwig
2018-04-05 22:17 ` Dan Williams
2018-04-06 7:03 ` Christoph Hellwig
2018-04-06 22:41 ` Dan Williams
2018-04-09 9:32 ` Christoph Hellwig
2018-04-11 16:06 ` Jeff Moyer
2018-04-11 16:27 ` Dan Williams
2018-04-11 17:27 ` Jeff Moyer
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