From: Christoph Hellwig <hch@infradead.org>
To: Matthew Wilcox <willy@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Matthew Wilcox <matthew.r.wilcox@intel.com>,
linux-fsdevel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 3/5] block: Add support for DAX on block devices
Date: Wed, 1 Jul 2015 00:19:15 -0700 [thread overview]
Message-ID: <20150701071915.GA31381@infradead.org> (raw)
In-Reply-To: <20150630195614.GG1971@linux.intel.com>
On Tue, Jun 30, 2015 at 03:56:15PM -0400, Matthew Wilcox wrote:
> > 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.
>
> O_DIRECT means "bypass the page cache", which is what this does (now it's
> able to apply to mmap too).
It never had a meaning for mmap.
> > 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.
>
> Um, we do support this for filesystems with DAX. The inconsistency we
> have is that if you have a direct-access-capable block device, currently
> files in a filesystem on it get the bypass-page-cache treatment, but if
> you use the raw block device directly, that mapping doesn't.
I don't see this O_DIRECT check done anywhere in filesystems.
Filesystems seems to get your O_DIRECT treatment when mounted with the
dax option as far as I can tell without the need for additional options.
The block device equivalent would be a sysfs flag, which seems like the
better implementation choice here.
next prev parent reply other threads:[~2015-07-01 7:19 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
2015-06-30 19:56 ` Matthew Wilcox
2015-07-01 7:19 ` Christoph Hellwig [this message]
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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