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From: Jan Kara <jack@suse.cz>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>, Christoph Hellwig <hch@infradead.org>,
	Johannes Thumshirn <jthumshirn@suse.de>,
	Dave Jiang <dave.jiang@intel.com>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	Linux MM <linux-mm@kvack.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-ext4 <linux-ext4@vger.kernel.org>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>
Subject: Re: Problems with VM_MIXEDMAP removal from /proc/<pid>/smaps
Date: Wed, 3 Oct 2018 18:44:07 +0200
Message-ID: <20181003164407.GK24030@quack2.suse.cz> (raw)
In-Reply-To: <CAPcyv4iJvN6_Cf6tw=5a=Uh99LfMFKU7n8QkGcz1ZaxL0Oi-3w@mail.gmail.com>

On Wed 03-10-18 08:13:37, Dan Williams wrote:
> On Wed, Oct 3, 2018 at 8:07 AM Jan Kara <jack@suse.cz> wrote:
> > WRT per-inode DAX property, AFAIU that inode flag is just going to be
> > advisory thing - i.e., use DAX if possible. If you mount a filesystem with
> > these inode flags set in a configuration which does not allow DAX to be
> > used, you will still be able to access such inodes but the access will use
> > page cache instead. And querying these flags should better show real
> > on-disk status and not just whether DAX is used as that would result in an
> > even bigger mess. So this feature seems to be somewhat orthogonal to the
> > API I'm looking for.
> 
> True, I imagine once we have that flag we will be able to distinguish
> the "saved" property and the "effective / live" property of DAX...
> Also it's really not DAX that applications care about as much as "is
> there page-cache indirection / overhead for this mapping?". That seems
> to be a narrower guarantee that we can make than what "DAX" might
> imply.

Right. So what do people think about my suggestion earlier in the thread to
use madvise(MADV_DIRECT_ACCESS) for this? Currently it would return success
when DAX is in use, failure otherwise. Later we could extend it to be also
used as a hint for caching policy for the inode...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply index

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-02 10:05 Jan Kara
2018-10-02 10:50 ` Michal Hocko
2018-10-02 13:32   ` Jan Kara
2018-10-02 12:10 ` Johannes Thumshirn
2018-10-02 14:20   ` Johannes Thumshirn
2018-10-02 14:45     ` Christoph Hellwig
2018-10-02 15:01       ` Johannes Thumshirn
2018-10-02 15:06         ` Christoph Hellwig
2018-10-04 10:09           ` Johannes Thumshirn
2018-10-05  6:25             ` Christoph Hellwig
2018-10-05  6:35               ` Johannes Thumshirn
2018-10-06  1:17                 ` Dan Williams
2018-10-14 15:47                   ` Dan Williams
2018-10-17 20:01                     ` Dan Williams
2018-10-18 17:43                       ` Jan Kara
2018-10-18 19:10                         ` Dan Williams
2018-10-19  3:01                           ` Dave Chinner
2018-10-02 14:29   ` Jan Kara
2018-10-02 14:37     ` Christoph Hellwig
2018-10-02 14:44       ` Johannes Thumshirn
2018-10-02 14:52         ` Christoph Hellwig
2018-10-02 15:31           ` Jan Kara
2018-10-02 20:18             ` Dan Williams
2018-10-03 12:50               ` Jan Kara
2018-10-03 14:38                 ` Dan Williams
2018-10-03 15:06                   ` Jan Kara
2018-10-03 15:13                     ` Dan Williams
2018-10-03 16:44                       ` Jan Kara [this message]
2018-10-03 21:13                         ` Dan Williams
2018-10-04 10:04                         ` Johannes Thumshirn
2018-10-02 15:07       ` Jan Kara
2018-10-17 20:23     ` Jeff Moyer
2018-10-18  0:25       ` Dave Chinner
2018-10-18 14:55         ` Jan Kara
2018-10-19  0:43           ` Dave Chinner
2018-10-30  6:30             ` Dan Williams
2018-10-30 22:49               ` Dave Chinner
2018-10-30 22:59                 ` Dan Williams
2018-10-31  5:59                 ` y-goto
2018-11-01 23:00                   ` Dave Chinner
2018-11-02  1:43                     ` y-goto
2018-10-18 21:05         ` Jeff Moyer
2018-10-09 19:43 ` Jeff Moyer
2018-10-16  8:25   ` Jan Kara
2018-10-16 12:35     ` Jeff Moyer

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