From: Christoph Hellwig <hch@infradead.org>
To: Matthew Wilcox <matthew.r.wilcox@intel.com>
Cc: linux-fsdevel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
Matthew Wilcox <willy@linux.intel.com>
Subject: Re: [PATCH 3/5] block: Add support for DAX on block devices
Date: Tue, 30 Jun 2015 04:19:49 -0700 [thread overview]
Message-ID: <20150630111949.GA28508@infradead.org> (raw)
In-Reply-To: <1435608152-6982-4-git-send-email-matthew.r.wilcox@intel.com>
On Mon, Jun 29, 2015 at 04:02:30PM -0400, Matthew Wilcox wrote:
> From: Matthew Wilcox <willy@linux.intel.com>
>
> Without this patch, accesses to a file on a filesystem on a block device
> could be done without the page cache, but accessing the block device
> itself would always go through the page cache.
>
> Now reads and writes to a block device that is capable of DAX will always
> bypass the page cache. Loads and stores to an mmapped block device will
> bypass the page cache if the user specified O_DIRECT. This opt-in from
> the user is necessary because DAX mappings are currently incompatible
> with RDMA and O_DIRECT I/Os with non-DAX files.
Using O_DIRECT for this seems like a pretty horrible hack, so I'd like
to see a really good justification of using this over other interfaces.
Also it needs a Cc to linux-api and an entry in the open man page, and
and even better explanation of why we only support this interface on
block devices but not file systems.
Last but least I supect we'll need a runtime option for direct_access
support in the brd devices, as we're now going to use the regular
block device path less and less.
next prev parent reply other threads:[~2015-06-30 11:19 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-29 20:02 [PATCH 0/5] DAX updates for 4.2 Matthew Wilcox
2015-06-29 20:02 ` [PATCH 1/5] dax: Add block size note to documentation Matthew Wilcox
2015-06-29 20:02 ` [PATCH 2/5] dax: Use copy_from_iter_nocache Matthew Wilcox
2015-06-29 20:02 ` [PATCH 3/5] block: Add support for DAX on block devices Matthew Wilcox
2015-06-30 11:19 ` Christoph Hellwig [this message]
2015-06-30 19:56 ` Matthew Wilcox
2015-07-01 7:19 ` Christoph Hellwig
2015-06-29 20:02 ` [PATCH 4/5] ext4: Use ext4_get_block_write() for DAX Matthew Wilcox
2015-06-29 20:02 ` [PATCH 5/5] vfs: Allow truncate, chomd and chown to be interrupted by fatal signals Matthew Wilcox
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