From: Dan Williams <dan.j.williams@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Boaz Harrosh <boaz@plexistor.com>,
linux-arch@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
riel@redhat.com, linux-raid <linux-raid@vger.kernel.org>,
linux-nvdimm <linux-nvdimm@ml01.01.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@infradead.org>,
Mel Gorman <mgorman@suse.de>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [Linux-nvdimm] [RFC PATCH 0/7] evacuate struct page from the block layer
Date: Thu, 19 Mar 2015 13:59:27 -0700 [thread overview]
Message-ID: <CAPcyv4j=M8V_36C-HhiJM7MHzNLFcpP=nec=LHnob5+qZ4xgYw@mail.gmail.com> (raw)
In-Reply-To: <20150319125917.6cc2bf02687aab542027d8ac@linux-foundation.org>
On Thu, Mar 19, 2015 at 12:59 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Thu, 19 Mar 2015 17:54:15 +0200 Boaz Harrosh <boaz@plexistor.com> wrote:
>
>> On 03/19/2015 03:43 PM, Matthew Wilcox wrote:
>> <>
>> >
>> > Dan missed "Support O_DIRECT to a mapped DAX file". More generally, if we
>> > want to be able to do any kind of I/O directly to persistent memory,
>> > and I think we do, we need to do one of:
>> >
>> > 1. Construct struct pages for persistent memory
>> > 1a. Permanently
>> > 1b. While the pages are under I/O
>> > 2. Teach the I/O layers to deal in PFNs instead of struct pages
>> > 3. Replace struct page with some other structure that can represent both
>> > DRAM and PMEM
>> >
>> > I'm personally a fan of #3, and I was looking at the scatterlist as
>> > my preferred data structure. I now believe the scatterlist as it is
>> > currently defined isn't sufficient, so we probably end up needing a new
>> > data structure. I think Dan's preferred method of replacing struct
>> > pages with PFNs is actually less instrusive, but doesn't give us as
>> > much advantage (an entirely new data structure would let us move to an
>> > extent based system at the same time, instead of sticking with an array
>> > of pages). Clearly Boaz prefers 1a, which works well enough for the
>> > 8GB NV-DIMMs, but not well enough for the 400GB NV-DIMMs.
>> >
>> > What's your preference? I guess option 0 is "force all I/O to go
>> > through the page cache and then get copied", but that feels like a nasty
>> > performance hit.
>>
>> Thanks Matthew, you have summarized it perfectly.
>>
>> I think #1b might have merit, as well.
>
> It would be interesting to see what a 1b implementation looks like and
> how it performs. We already allocate a bunch of temporary things to
> support in-flight IO (bio, request) and allocating pageframes on the
> same basis seems a fairly logical fit.
At least for block-i/o it seems the only place we really need struct
page infrastructure is for kmap(). Given we already need a kmap_pfn()
solution for option 2 a "dynamic allocation" stop along that
development path may just naturally fall out.
next prev parent reply other threads:[~2015-03-19 20:59 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-16 20:25 [RFC PATCH 0/7] evacuate struct page from the block layer Dan Williams
2015-03-16 20:25 ` [RFC PATCH 1/7] block: add helpers for accessing a bio_vec page Dan Williams
2015-03-16 20:25 ` [RFC PATCH 2/7] block: convert bio_vec.bv_page to bv_pfn Dan Williams
2015-03-16 23:05 ` Al Viro
2015-03-17 13:02 ` Matthew Wilcox
2015-03-17 15:53 ` Dan Williams
2015-03-16 20:25 ` [RFC PATCH 3/7] dma-mapping: allow archs to optionally specify a ->map_pfn() operation Dan Williams
2015-03-18 11:21 ` [Linux-nvdimm] " Boaz Harrosh
2015-03-16 20:25 ` [RFC PATCH 4/7] scatterlist: use sg_phys() Dan Williams
2015-03-16 20:25 ` [RFC PATCH 5/7] scatterlist: support "page-less" (__pfn_t only) entries Dan Williams
2015-03-16 20:25 ` [RFC PATCH 6/7] x86: support dma_map_pfn() Dan Williams
2015-03-16 20:26 ` [RFC PATCH 7/7] block: base support for pfn i/o Dan Williams
2015-03-18 10:47 ` [RFC PATCH 0/7] evacuate struct page from the block layer Boaz Harrosh
2015-03-18 13:06 ` Matthew Wilcox
2015-03-18 14:38 ` [Linux-nvdimm] " Boaz Harrosh
2015-03-20 15:56 ` Rik van Riel
2015-03-22 11:53 ` Boaz Harrosh
2015-03-18 15:35 ` Dan Williams
2015-03-18 20:26 ` Andrew Morton
2015-03-19 13:43 ` Matthew Wilcox
2015-03-19 15:54 ` [Linux-nvdimm] " Boaz Harrosh
2015-03-19 19:59 ` Andrew Morton
2015-03-19 20:59 ` Dan Williams [this message]
2015-03-22 17:22 ` Boaz Harrosh
2015-03-20 17:32 ` Wols Lists
2015-03-22 10:30 ` Boaz Harrosh
2015-03-19 18:17 ` Christoph Hellwig
2015-03-19 19:31 ` Matthew Wilcox
2015-03-22 16:46 ` Boaz Harrosh
2015-03-20 16:21 ` Rik van Riel
2015-03-20 20:31 ` Matthew Wilcox
2015-03-20 21:08 ` Rik van Riel
2015-03-22 17:06 ` Boaz Harrosh
2015-03-22 17:22 ` Dan Williams
2015-03-22 17:39 ` Boaz Harrosh
2015-03-20 21:17 ` Wols Lists
2015-03-22 16:24 ` Boaz Harrosh
2015-03-22 15:51 ` Boaz Harrosh
2015-03-23 15:19 ` Rik van Riel
2015-03-23 19:30 ` Christoph Hellwig
2015-03-24 9:41 ` Boaz Harrosh
2015-03-24 16:57 ` Rik van Riel
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='CAPcyv4j=M8V_36C-HhiJM7MHzNLFcpP=nec=LHnob5+qZ4xgYw@mail.gmail.com' \
--to=dan.j.williams@intel.com \
--cc=akpm@linux-foundation.org \
--cc=axboe@kernel.dk \
--cc=boaz@plexistor.com \
--cc=dave.hansen@linux.intel.com \
--cc=hch@infradead.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-nvdimm@ml01.01.org \
--cc=linux-raid@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=riel@redhat.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).