From: Michal Hocko <mhocko@kernel.org>
To: Jann Horn <jannh@google.com>
Cc: Prakash Sangappa <prakash.sangappa@oracle.com>,
Dave Hansen <dave.hansen@intel.com>,
Anshuman Khandual <khandual@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
kernel list <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Linux API <linux-api@vger.kernel.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
n-horiguchi@ah.jp.nec.com, Ulrich Drepper <drepper@gmail.com>,
David Rientjes <rientjes@google.com>,
Horiguchi Naoya <nao.horiguchi@gmail.com>,
steven.sistare@oracle.com
Subject: Re: [RFC PATCH] Add /proc/<pid>/numa_vamaps for numa node information
Date: Fri, 14 Sep 2018 15:49:05 +0200 [thread overview]
Message-ID: <20180914134905.GA6081@dhcp22.suse.cz> (raw)
In-Reply-To: <CAG48ez2RSn-EQkf-ahs41tOKpzt23JMGYZxUtWMRPe8c5jAq-A@mail.gmail.com>
On Fri 14-09-18 14:49:10, Jann Horn wrote:
> On Fri, Sep 14, 2018 at 8:21 AM Michal Hocko <mhocko@kernel.org> wrote:
> > On Fri 14-09-18 03:33:28, Jann Horn wrote:
> > > On Wed, Sep 12, 2018 at 10:43 PM prakash.sangappa
> > > <prakash.sangappa@oracle.com> wrote:
> > > > On 05/09/2018 04:31 PM, Dave Hansen wrote:
> > > > > On 05/07/2018 06:16 PM, prakash.sangappa wrote:
> > > > >> It will be /proc/<pid>/numa_vamaps. Yes, the behavior will be
> > > > >> different with respect to seeking. Output will still be text and
> > > > >> the format will be same.
> > > > >>
> > > > >> I want to get feedback on this approach.
> > > > > I think it would be really great if you can write down a list of the
> > > > > things you actually want to accomplish. Dare I say: you need a
> > > > > requirements list.
> > > > >
> > > > > The numa_vamaps approach continues down the path of an ever-growing list
> > > > > of highly-specialized /proc/<pid> files. I don't think that is
> > > > > sustainable, even if it has been our trajectory for many years.
> > > > >
> > > > > Pagemap wasn't exactly a shining example of us getting new ABIs right,
> > > > > but it sounds like something along those is what we need.
> > > >
> > > > Just sent out a V2 patch. This patch simplifies the file content. It
> > > > only provides VA range to numa node id information.
> > > >
> > > > The requirement is basically observability for performance analysis.
> > > >
> > > > - Need to be able to determine VA range to numa node id information.
> > > > Which also gives an idea of which range has memory allocated.
> > > >
> > > > - The proc file /proc/<pid>/numa_vamaps is in text so it is easy to
> > > > directly view.
> > > >
> > > > The V2 patch supports seeking to a particular process VA from where
> > > > the application could read the VA to numa node id information.
> > > >
> > > > Also added the 'PTRACE_MODE_READ_REALCREDS' check when opening the
> > > > file /proc file as was indicated by Michal Hacko
> > >
> > > procfs files should use PTRACE_MODE_*_FSCREDS, not PTRACE_MODE_*_REALCREDS.
> >
> > Out of my curiosity, what is the semantic difference? At least
> > kernel_move_pages uses PTRACE_MODE_READ_REALCREDS. Is this a bug?
>
> No, that's fine. REALCREDS basically means "look at the caller's real
> UID for the access check", while FSCREDS means "look at the caller's
> filesystem UID". The ptrace access check has historically been using
> the real UID, which is sorta weird, but normally works fine. Given
> that this is documented, I didn't see any reason to change it for most
> things that do ptrace access checks, even if the EUID would IMO be
> more appropriate. But things that capture caller credentials at points
> like open() really shouldn't look at the real UID; instead, they
> should use the filesystem UID (which in practice is basically the same
> as the EUID).
>
> So in short, it depends on the interface you're coming through: Direct
> syscalls use REALCREDS, things that go through the VFS layer use
> FSCREDS.
Ahh, OK, I see. Thanks for the clarification! Then I agree that the proc
interface should use FSCREDS.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-09-14 13:49 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-02 5:58 [RFC PATCH] Add /proc/<pid>/numa_vamaps for numa node information Prakash Sangappa
2018-05-02 21:33 ` Andrew Morton
2018-05-02 22:28 ` Dave Hansen
2018-05-02 23:17 ` prakash.sangappa
2018-05-03 8:46 ` Anshuman Khandual
2018-05-03 22:27 ` prakash.sangappa
2018-05-03 22:26 ` Dave Hansen
2018-05-07 23:22 ` prakash.sangappa
2018-05-08 0:05 ` Dave Hansen
2018-05-08 1:16 ` prakash.sangappa
2018-05-09 23:31 ` Dave Hansen
2018-09-12 20:42 ` prakash.sangappa
2018-09-12 20:57 ` prakash.sangappa
2018-09-14 1:33 ` Jann Horn
2018-09-14 6:21 ` Michal Hocko
2018-09-14 12:49 ` Jann Horn
2018-09-14 13:49 ` Michal Hocko [this message]
2018-09-14 18:07 ` Prakash Sangappa
2018-09-14 18:14 ` Jann Horn
2018-05-02 23:43 ` prakash.sangappa
2018-05-03 8:57 ` Michal Hocko
2018-05-03 22:37 ` prakash.sangappa
2018-05-04 11:10 ` Michal Hocko
2018-05-03 18:03 ` Christopher Lameter
2018-05-03 22:39 ` prakash.sangappa
2018-05-04 11:12 ` Michal Hocko
2018-05-04 16:18 ` Prakash Sangappa
2018-05-10 7:42 ` Michal Hocko
2018-05-10 16:00 ` Prakash Sangappa
2018-05-11 6:39 ` Michal Hocko
2018-05-04 14:57 ` Christopher Lameter
2018-05-04 16:27 ` Prakash Sangappa
2018-05-07 14:47 ` Christopher Lameter
2018-05-07 22:50 ` prakash.sangappa
2018-05-08 12:53 ` Christopher Lameter
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