From: Andrew Morton <akpm@linux-foundation.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Calvin Owens <calvinowens@fb.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Miklos Szeredi <miklos@szeredi.hu>, Zefan Li <lizefan@huawei.com>,
Oleg Nesterov <oleg@redhat.com>, Joe Perches <joe@perches.com>,
David Howells <dhowells@redhat.com>,
Linux Kernel <linux-kernel@vger.kernel.org>,
kernel-team@fb.com, Andy Lutomirski <luto@amacapital.net>,
Cyrill Gorcunov <gorcunov@openvz.org>,
Kees Cook <keescook@chromium.org>,
"Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH v6] procfs: Always expose /proc/<pid>/map_files/ and make it readable
Date: Thu, 11 Jun 2015 11:49:46 -0700 [thread overview]
Message-ID: <20150611114946.d9d259a363a86adba756bdfd@linux-foundation.org> (raw)
In-Reply-To: <CACVxJT_2hVCjg5apS-wcuFRPdZD91FUX_9drrUxDXqTq1Px7mg@mail.gmail.com>
On Thu, 11 Jun 2015 14:10:45 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
> On Wed, Jun 10, 2015 at 11:58 PM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
> > On Tue, 9 Jun 2015 18:39:02 -0700 Calvin Owens <calvinowens@fb.com> wrote:
> >
> >> On Tuesday 06/09 at 14:13 -0700, Andrew Morton wrote:
> >> > On Mon, 8 Jun 2015 20:39:33 -0700 Calvin Owens <calvinowens@fb.com> wrote:
> >> >
> >> > > Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
> >> > > is only exposed if CONFIG_CHECKPOINT_RESTORE is set.
> >> > >
> >> > > This interface very useful because it allows userspace to stat()
> >> > > deleted files that are still mapped by some process, which enables a
> >> > > much quicker and more accurate answer to the question "How much disk
> >> > > space is being consumed by files that are deleted but still mapped?"
> >> > > than is currently possible.
> >> >
> >> > Why is that information useful?
> >> >
> >> > I could perhaps think of some use for "How much disk space is being
> >> > consumed by files that are deleted but still open", but to count the
> >> > mmapped-then-unlinked files while excluding the opened-then-unlinked
> >> > files seems damned peculiar.
> >>
> >> Let's phrase the question a bit more generically:
> >>
> >> "How much disk space is being consumed by files that have been
> >> unlinked, but are still referenced by some process?"
> >>
> >> There are two pieces to this problem:
> >> 1) Unlinked files that are still open (whether mapped or not)
> >> 2) Unlinked files that are not open, but are still mapped
> >>
> >> You can track down everything in (1) using /proc/<pid>/fd/*, and you
> >> can use stat() to figure out how much space they're using.
> >
> > This doesn't work if the mapped file has been unlinked? What does the
> > /proc/pid/map_files listing look like for these?
>
> It says "(deleted)" like /proc/*/exe or any other symlink.
Actually the symlink directs at "/home/akpm/foo (deleted)".
And lo, if you do `stat -L' on the symlink, you get the info for the
unlinked-but-still-mmapped inode. I never knew that. And I wouldn't
have learned it from the documentation, which is careful to keep all
this a secret.
next prev parent reply other threads:[~2015-06-11 18:49 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-14 0:20 [RFC][PATCH] procfs: Add /proc/<pid>/mapped_files Calvin Owens
2015-01-14 0:23 ` Calvin Owens
2015-01-14 14:13 ` Rasmus Villemoes
2015-01-14 14:37 ` Siddhesh Poyarekar
2015-01-14 14:53 ` Rasmus Villemoes
2015-01-14 21:03 ` Calvin Owens
2015-01-14 22:45 ` Andrew Morton
2015-01-14 23:51 ` Rasmus Villemoes
2015-01-16 1:15 ` Andrew Morton
2015-01-16 11:00 ` Kirill A. Shutemov
2015-01-14 15:25 ` Kirill A. Shutemov
2015-01-14 15:33 ` Cyrill Gorcunov
2015-01-14 20:46 ` Calvin Owens
2015-01-14 21:16 ` Cyrill Gorcunov
2015-01-22 2:45 ` [RFC][PATCH] procfs: Always expose /proc/<pid>/map_files/ and make it readable Calvin Owens
2015-01-22 7:16 ` Cyrill Gorcunov
2015-01-22 11:02 ` Kirill A. Shutemov
2015-01-22 21:00 ` Calvin Owens
2015-01-22 21:27 ` Kirill A. Shutemov
2015-01-23 5:52 ` Calvin Owens
2015-01-24 3:15 ` [RFC][PATCH v2] " Calvin Owens
2015-01-26 12:47 ` Kirill A. Shutemov
2015-01-26 21:00 ` Cyrill Gorcunov
2015-01-26 23:43 ` Andrew Morton
2015-01-27 0:15 ` Kees Cook
2015-01-27 7:37 ` Cyrill Gorcunov
2015-01-27 19:53 ` Kees Cook
2015-01-27 21:35 ` Cyrill Gorcunov
2015-01-27 21:46 ` Pavel Emelyanov
2015-01-27 0:19 ` Kirill A. Shutemov
2015-01-27 6:46 ` Cyrill Gorcunov
2015-01-27 6:50 ` Andrew Morton
2015-01-27 7:23 ` Cyrill Gorcunov
2015-01-28 4:38 ` Calvin Owens
2015-01-30 1:30 ` Kees Cook
2015-01-31 1:58 ` Calvin Owens
2015-02-02 14:01 ` Austin S Hemmelgarn
2015-02-04 3:53 ` Calvin Owens
2015-02-02 20:16 ` Andy Lutomirski
2015-02-04 3:28 ` Calvin Owens
2015-02-12 2:29 ` [RFC][PATCH v3] " Calvin Owens
2015-02-12 7:45 ` Cyrill Gorcunov
2015-02-14 20:40 ` [RFC][PATCH v4] " Calvin Owens
2015-03-10 22:17 ` Cyrill Gorcunov
2015-04-28 22:23 ` Calvin Owens
2015-04-29 7:32 ` Cyrill Gorcunov
2015-05-19 3:10 ` [PATCH v5] " Calvin Owens
2015-05-19 3:29 ` Joe Perches
2015-05-19 18:04 ` Andy Lutomirski
2015-05-21 1:52 ` Calvin Owens
2015-05-21 2:10 ` Andy Lutomirski
2015-06-09 3:39 ` [PATCH v6] " Calvin Owens
2015-06-09 17:27 ` Kees Cook
2015-06-09 17:47 ` Andy Lutomirski
2015-06-09 18:15 ` Cyrill Gorcunov
2015-06-09 21:13 ` Andrew Morton
2015-06-10 1:39 ` Calvin Owens
2015-06-10 20:58 ` Andrew Morton
2015-06-11 11:10 ` Alexey Dobriyan
2015-06-11 18:49 ` Andrew Morton [this message]
2015-06-12 9:55 ` Alexey Dobriyan
2015-06-19 2:32 ` [PATCH v7] " Calvin Owens
2015-07-15 22:21 ` Andrew Morton
2015-07-15 23:39 ` Calvin Owens
2015-02-14 20:44 ` [PATCH] procfs: Return -ESRCH on /proc/N/fd/* when PID N doesn't exist Calvin Owens
2015-01-14 22:40 ` [RFC][PATCH] procfs: Add /proc/<pid>/mapped_files Kirill A. Shutemov
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