From: Jan Kara <jack@suse.cz>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>, Jens Axboe <axboe@fb.com>,
Jan Kara <jack@suse.cz>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Jeff Moyer <jmoyer@redhat.com>, Jan Kara <jack@suse.com>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v3 02/15] dax: increase granularity of dax_clear_blocks() operations
Date: Tue, 3 Nov 2015 17:21:19 +0100 [thread overview]
Message-ID: <20151103162119.GE4063@quack.suse.cz> (raw)
In-Reply-To: <CAPcyv4iwiTMMWGE63KX_tzrH1_pEpPxzAvRNgpaDEXAOhXU1BA@mail.gmail.com>
On Mon 02-11-15 21:31:11, Dan Williams wrote:
> On Mon, Nov 2, 2015 at 8:48 PM, Dave Chinner <david@fromorbit.com> wrote:
> > On Mon, Nov 02, 2015 at 07:27:26PM -0800, Dan Williams wrote:
> >> On Mon, Nov 2, 2015 at 4:51 PM, Dave Chinner <david@fromorbit.com> wrote:
> >> > On Sun, Nov 01, 2015 at 11:29:53PM -0500, Dan Williams wrote:
> >> > The zeroing (and the data, for that matter) doesn't need to be
> >> > committed to persistent store until the allocation is written and
> >> > committed to the journal - that will happen with a REQ_FLUSH|REQ_FUA
> >> > write, so it makes sense to deploy the big hammer and delay the
> >> > blocking CPU cache flushes until the last possible moment in cases
> >> > like this.
> >>
> >> In pmem terms that would be a non-temporal memset plus a delayed
> >> wmb_pmem at REQ_FLUSH time. Better to write around the cache than
> >> loop over the dirty-data issuing flushes after the fact. We'll bump
> >> the priority of the non-temporal memset implementation.
> >
> > Why is it better to do two synchronous physical writes to memory
> > within a couple of microseconds of CPU time rather than writing them
> > through the cache and, in most cases, only doing one physical write
> > to memory in a separate context that expects to wait for a flush
> > to complete?
>
> With a switch to non-temporal writes they wouldn't be synchronous,
> although it's doubtful that the subsequent writes after zeroing would
> also hit the store buffer.
>
> If we had a method to flush by physical-cache-way rather than a
> virtual address then it would indeed be better to save up for one
> final flush, but when we need to resort to looping through all the
> virtual addresses that might have touched it gets expensive.
Similarly as Dave I'm somewhat confused by your use of "virtual addresses"
and I wasn't able to figure out what exactly are you speaking about. In
Ross' patches, fsync will iterate over all 4 KB ranges (they would be pages
if we had page cache) of the file that got dirtied and call wb_cache_pmem()
for each corresponding "physical block" - where "physical block" actually
ends up being an physical address in pmem. Is this iteration what you find
too costly?
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2015-11-03 16:21 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-02 4:29 [PATCH v3 00/15] block, dax updates for 4.4 Dan Williams
2015-11-02 4:29 ` [PATCH v3 01/15] pmem, dax: clean up clear_pmem() Dan Williams
2015-11-02 4:29 ` [PATCH v3 02/15] dax: increase granularity of dax_clear_blocks() operations Dan Williams
2015-11-03 0:51 ` Dave Chinner
2015-11-03 3:27 ` Dan Williams
2015-11-03 4:48 ` Dave Chinner
2015-11-03 5:31 ` Dan Williams
2015-11-03 5:52 ` Dave Chinner
2015-11-03 7:24 ` Dan Williams
2015-11-03 16:21 ` Jan Kara [this message]
2015-11-03 17:57 ` Ross Zwisler
2015-11-03 20:59 ` Dave Chinner
2015-11-02 4:29 ` [PATCH v3 03/15] block, dax: fix lifetime of in-kernel dax mappings with dax_map_atomic() Dan Williams
2015-11-03 19:01 ` Ross Zwisler
2015-11-03 19:09 ` Jeff Moyer
2015-11-03 22:50 ` Dan Williams
2016-01-18 10:42 ` Geert Uytterhoeven
2015-11-02 4:30 ` [PATCH v3 04/15] libnvdimm, pmem: move request_queue allocation earlier in probe Dan Williams
2015-11-03 19:15 ` Ross Zwisler
2015-11-02 4:30 ` [PATCH v3 05/15] libnvdimm, pmem: fix size trim in pmem_direct_access() Dan Williams
2015-11-03 19:32 ` Ross Zwisler
2015-11-03 21:39 ` Dan Williams
2015-11-02 4:30 ` [PATCH v3 06/15] um: kill pfn_t Dan Williams
2015-11-02 4:30 ` [PATCH v3 07/15] kvm: rename pfn_t to kvm_pfn_t Dan Williams
2015-11-02 4:30 ` [PATCH v3 08/15] mm, dax, pmem: introduce pfn_t Dan Williams
2015-11-02 16:30 ` Joe Perches
2015-11-02 4:30 ` [PATCH v3 09/15] block: notify queue death confirmation Dan Williams
2015-11-02 4:30 ` [PATCH v3 10/15] dax, pmem: introduce zone_device_revoke() and devm_memunmap_pages() Dan Williams
2015-11-02 4:30 ` [PATCH v3 11/15] block: introduce bdev_file_inode() Dan Williams
2015-11-02 4:30 ` [PATCH v3 12/15] block: enable dax for raw block devices Dan Williams
2015-11-02 4:30 ` [PATCH v3 13/15] block, dax: make dax mappings opt-in by default Dan Williams
2015-11-03 0:32 ` Dave Chinner
2015-11-03 7:35 ` Dan Williams
2015-11-03 20:20 ` Dave Chinner
2015-11-03 23:04 ` Dan Williams
2015-11-04 19:23 ` Dan Williams
2015-11-02 4:30 ` [PATCH v3 14/15] dax: dirty extent notification Dan Williams
2015-11-03 1:16 ` Dave Chinner
2015-11-03 4:56 ` Dan Williams
2015-11-03 5:40 ` Dave Chinner
2015-11-03 7:20 ` Dan Williams
2015-11-03 20:51 ` Dave Chinner
2015-11-03 21:19 ` Dan Williams
2015-11-03 21:37 ` Ross Zwisler
2015-11-03 21:43 ` Dan Williams
2015-11-03 21:18 ` Ross Zwisler
2015-11-03 21:34 ` Dan Williams
2015-11-02 4:31 ` [PATCH v3 15/15] pmem: blkdev_issue_flush support Dan Williams
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