From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org,
"Darrick J. Wong" <darrick.wong@oracle.com>,
"Theodore Ts'o" <tytso@mit.edu>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andreas Dilger <adilger.kernel@dilger.ca>,
Christoph Hellwig <hch@lst.de>,
Dan Williams <dan.j.williams@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Ingo Molnar <mingo@redhat.com>, Jan Kara <jack@suse.cz>,
Jonathan Corbet <corbet@lwn.net>,
Matthew Wilcox <mawilcox@microsoft.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-nvdimm@lists.01.org, linux-xfs@vger.kernel.org
Subject: Re: [PATCH v3 0/5] DAX common 4k zero page
Date: Fri, 30 Jun 2017 13:05:56 -0600 [thread overview]
Message-ID: <20170630190556.GB27371@linux.intel.com> (raw)
In-Reply-To: <20170628220152.28161-1-ross.zwisler@linux.intel.com>
On Wed, Jun 28, 2017 at 04:01:47PM -0600, Ross Zwisler wrote:
> When servicing mmap() reads from file holes the current DAX code allocates
> a page cache page of all zeroes and places the struct page pointer in the
> mapping->page_tree radix tree. This has three major drawbacks:
>
> 1) It consumes memory unnecessarily. For every 4k page that is read via a
> DAX mmap() over a hole, we allocate a new page cache page. This means that
> if you read 1GiB worth of pages, you end up using 1GiB of zeroed memory.
>
> 2) It is slower than using a common zero page because each page fault has
> more work to do. Instead of just inserting a common zero page we have to
> allocate a page cache page, zero it, and then insert it.
>
> 3) The fact that we had to check for both DAX exceptional entries and for
> page cache pages in the radix tree made the DAX code more complex.
>
> This series solves these issues by following the lead of the DAX PMD code
> and using a common 4k zero page instead. This reduces memory usage and
> decreases latencies for some workloads, and it simplifies the DAX code,
> removing over 100 lines in total.
>
> Andrew, I'm still hoping to get this merged for v4.13 if possible. I I have
> addressed all of Jan's feedback, but he is on vacation for the next few
> weeks so he may not be able to give me Reviewed-by tags. I think this
> series is relatively low risk with clear benefits, and I think we should be
> able to address any issues that come up during the v4.13 RC series.
>
> This series has passed my targeted testing and a full xfstests run on both
> XFS and ext4.
This series has also passed the automated 0-day kernel builds in 168 configs.
prev parent reply other threads:[~2017-06-30 19:06 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-28 22:01 [PATCH v3 0/5] DAX common 4k zero page Ross Zwisler
2017-06-28 22:01 ` [PATCH v3 1/5] mm: add vm_insert_mixed_mkwrite() Ross Zwisler
2017-07-19 14:16 ` Jan Kara
2017-07-19 17:51 ` Ross Zwisler
2017-07-19 21:58 ` Ross Zwisler
2017-07-21 17:44 ` Ross Zwisler
2017-07-24 11:20 ` Jan Kara
2017-07-20 15:26 ` Vivek Goyal
2017-07-20 15:59 ` Ross Zwisler
2017-07-21 18:02 ` Ross Zwisler
2017-06-28 22:01 ` [PATCH v3 2/5] dax: relocate some dax functions Ross Zwisler
2017-06-28 22:01 ` [PATCH v3 3/5] dax: use common 4k zero page for dax mmap reads Ross Zwisler
2017-07-19 15:33 ` Jan Kara
2017-07-19 16:26 ` Ross Zwisler
2017-07-20 10:27 ` Jan Kara
2017-07-20 14:28 ` Ross Zwisler
2017-06-28 22:01 ` [PATCH v3 4/5] dax: remove DAX code from page_cache_tree_insert() Ross Zwisler
2017-06-28 22:01 ` [PATCH v3 5/5] dax: move all DAX radix tree defs to fs/dax.c Ross Zwisler
2017-06-30 19:05 ` Ross Zwisler [this message]
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=20170630190556.GB27371@linux.intel.com \
--to=ross.zwisler@linux.intel.com \
--cc=adilger.kernel@dilger.ca \
--cc=akpm@linux-foundation.org \
--cc=corbet@lwn.net \
--cc=dan.j.williams@intel.com \
--cc=darrick.wong@oracle.com \
--cc=dave.hansen@intel.com \
--cc=hch@lst.de \
--cc=jack@suse.cz \
--cc=linux-doc@vger.kernel.org \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-nvdimm@lists.01.org \
--cc=linux-xfs@vger.kernel.org \
--cc=mawilcox@microsoft.com \
--cc=mingo@redhat.com \
--cc=rostedt@goodmis.org \
--cc=tytso@mit.edu \
--cc=viro@zeniv.linux.org.uk \
/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).