linux-kernel - Re: [PATCH v3 3/5] /dev/dax, core: file operations and dax-mmap

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Date:	Fri, 20 May 2016 09:58:33 +0200
From:	Johannes Thumshirn <jthumshirn@...e.de>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	linux-nvdimm@...ts.01.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, hch@....de,
	linux-block@...r.kernel.org, Hannes Reinecke <hare@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3 3/5] /dev/dax, core: file operations and dax-mmap

On Wed, May 18, 2016 at 01:56:22PM -0700, Dan Williams wrote:
> The "Device DAX" core enables dax mappings of performance / feature
> differentiated memory.  An open mapping or file handle keeps the backing
> struct device live, but new mappings are only possible while the device
> is enabled.   Faults are handled under rcu_read_lock to synchronize
> with the enabled state of the device.
> 
> Similar to the filesystem-dax case the backing memory may optionally
> have struct page entries.  However, unlike fs-dax there is no support
> for private mappings, or mappings that are not backed by media (see
> use of zero-page in fs-dax).
> 
> Mappings are always guaranteed to match the alignment of the dax_region.
> If the dax_region is configured to have a 2MB alignment, all mappings
> are guaranteed to be backed by a pmd entry.  Contrast this determinism
> with the fs-dax case where pmd mappings are opportunistic.  If userspace
> attempts to force a misaligned mapping, the driver will fail the mmap
> attempt.  See dax_dev_check_vma() for other scenarios that are rejected,
> like MAP_PRIVATE mappings.
> 
> Cc: Hannes Reinecke <hare@...e.de>
> Cc: Jeff Moyer <jmoyer@...hat.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Acked-by: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

OK from my side,
Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>

-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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