Linux-Fsdevel Archive on lore.kernel.org
 help / color / Atom feed
From: Christoph Hellwig <hch@infradead.org>
To: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>, Jan Kara <jack@suse.cz>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-nvdimm@lists.01.org, mhocko@suse.cz,
	Dan Williams <dan.j.williams@intel.com>
Subject: Re: Problems with VM_MIXEDMAP removal from /proc/<pid>/smaps
Date: Tue, 2 Oct 2018 08:06:34 -0700
Message-ID: <20181002150634.GA22209@infradead.org> (raw)
In-Reply-To: <20181002150123.GD4963@linux-x5ow.site>

On Tue, Oct 02, 2018 at 05:01:24PM +0200, Johannes Thumshirn wrote:
> On Tue, Oct 02, 2018 at 07:45:47AM -0700, Christoph Hellwig wrote:
> > How does an application "make use of DAX"?  What actual user visible
> > semantics are associated with a file that has this flag set?
> 
> There may not be any user visible semantics of DAX, but there are
> promises we gave to application developers praising DAX as _the_
> method to map data on persistent memory and get around "the penalty of
> the page cache" (however big this is).

Who is "we"?  As someone involved with DAX code I think it is a steaming
pile of *****, and we are still looking for cases where it actually
works without bugs.  That's why the experimental tag still is on it
for example.

> As I said in another mail to this thread, applications have started to
> poke in procfs to see whether they can use DAX or not.

And what are they actually doing with that?

> 
> Party A has promised party B

We have never promised anyone anything.

> So technically e1fb4a086495 is a user visible regression and in the
> past we have reverted patches introducing these, even if the patch is
> generally correct and poking in /proc/self/smaps is a bad idea.

What actually stops working here and why?  If some stupid app doesn't work
without mixedmap and we want to apply the don't break userspace mantra
hard we should just always expose it.

> I just wanted to give them a documented way to check for this
> promise. Being neutral if this promise is right or wrong, good or bad,
> or whatever. That's not my call, but I prefer not having angry users,
> yelling at me because of broken applications.

There is no promise, sorry.

  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 [this message]
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
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

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20181002150634.GA22209@infradead.org \
    --to=hch@infradead.org \
    --cc=dan.j.williams@intel.com \
    --cc=jack@suse.cz \
    --cc=jthumshirn@suse.de \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-nvdimm@lists.01.org \
    --cc=mhocko@suse.cz \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Fsdevel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-fsdevel/0 linux-fsdevel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-fsdevel linux-fsdevel/ https://lore.kernel.org/linux-fsdevel \
		linux-fsdevel@vger.kernel.org linux-fsdevel@archiver.kernel.org
	public-inbox-index linux-fsdevel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-fsdevel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox