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From: Dan Williams <dan.j.williams@intel.com>
To: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>, Jan Kara <jack@suse.cz>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	Michal Hocko <mhocko@suse.cz>
Subject: Re: Problems with VM_MIXEDMAP removal from /proc/<pid>/smaps
Date: Fri, 5 Oct 2018 18:17:29 -0700
Message-ID: <CAPcyv4jD4VgRaKDQF9eMmjhMEHjUJqRU8i6OC+-=0domCc9u3A@mail.gmail.com> (raw)
In-Reply-To: <20181005063519.GA5491@linux-x5ow.site>

On Thu, Oct 4, 2018 at 11:35 PM Johannes Thumshirn <jthumshirn@suse.de> wrote:
>
> On Thu, Oct 04, 2018 at 11:25:24PM -0700, Christoph Hellwig wrote:
> > Since when is an article on some website a promise (of what exactly)
> > by linux kernel developers?
>
> Let's stop it here, this doesn't make any sort of forward progress.
>

I do think there is some progress we can make if we separate DAX as an
access mechanism vs DAX as a resource utilization contract. My attempt
at representing Christoph's position is that the kernel should not be
advertising / making access mechanism guarantees. That makes sense.
Even with MAP_SYNC+DAX the kernel reserves the right to write-protect
mappings at will and trap access into a kernel handler. Additionally,
whether read(2) / write(2) does anything different behind the scenes
in DAX mode, or not should be irrelevant to the application.

That said what is certainly not irrelevant is a kernel giving
userspace visibility and control into resource utilization. Jan's
MADV_DIRECT_ACCESS let's the application make assumptions about page
cache utilization, we just need to another mechanism to read if a
mapping is effectively already in that state.

  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 [this message]
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
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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