From: Michal Hocko <mhocko@kernel.org>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
Alexey Dobriyan <adobriyan@gmail.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-api@vger.kernel.org
Subject: Re: [RFC PATCH] mm, proc: report PR_SET_THP_DISABLE in proc
Date: Mon, 15 Oct 2018 17:03:25 +0200 [thread overview]
Message-ID: <20181015150325.GN18839@dhcp22.suse.cz> (raw)
In-Reply-To: <20181009083326.GG8528@dhcp22.suse.cz>
On Tue 09-10-18 10:33:26, Michal Hocko wrote:
> On Thu 04-10-18 11:34:11, David Rientjes wrote:
> > On Thu, 4 Oct 2018, Michal Hocko wrote:
> >
> > > > And prior to the offending commit, there were three ways to control thp
> > > > but two ways to determine if a mapping was eligible for thp based on the
> > > > implementation detail of one of those ways.
> > >
> > > Yes, it is really unfortunate that we have ever allowed to leak such an
> > > internal stuff like VMA flags to userspace.
> > >
> >
> > Right, I don't like userspace dependencies on VmFlags in smaps myself, but
> > it's the only way we have available that shows whether a single mapping is
> > eligible to be backed by thp :/
>
> Which is not the case due to reasons mentioned earlier. It only speaks
> about madvise status on the VMA.
>
> > > > If there are three ways to
> > > > control thp, userspace is still in the dark wrt which takes precedence
> > > > over the other: we have PR_SET_THP_DISABLE but globally sysfs has it set
> > > > to "always", or we have MADV_HUGEPAGE set per smaps but PR_SET_THP_DISABLE
> > > > shown in /proc/pid/status, etc.
> > > >
> > > > Which one is the ultimate authority?
> > >
> > > Isn't our documentation good enough? If not then we should document it
> > > properly.
> > >
> >
> > No, because the offending commit actually changed the precedence itself:
> > PR_SET_THP_DISABLE used to be honored for future mappings and the commit
> > changed that for all current mappings.
>
> Which is the actual and the full point of the fix as described in the
> changelog. The original implementation was poor and inconsistent.
>
> > So as a result of the commit
> > itself we would have had to change the documentation and userspace can't
> > be expected to keep up with yet a fourth variable: kernel version. It
> > really needs to be simpler, just a per-mapping specifier.
>
> As I've said, if you really need a per-vma granularity then make it a
> dedicated line in the output with a clear semantic. Do not make VMA
> flags even more confusing.
Can we settle with something please?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-10-15 15:03 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-24 17:55 [patch] mm, thp: always specify ineligible vmas as nh in smaps David Rientjes
2018-09-24 18:25 ` Vlastimil Babka
2018-09-24 19:17 ` David Rientjes
2018-09-24 19:30 ` [patch v2] " David Rientjes
2018-09-24 19:56 ` Michal Hocko
2018-09-24 20:02 ` Michal Hocko
2018-09-24 20:43 ` Vlastimil Babka
2018-09-25 5:50 ` Michal Hocko
2018-09-25 19:52 ` David Rientjes
2018-09-25 20:29 ` Michal Hocko
2018-09-25 21:45 ` David Rientjes
2018-09-25 22:04 ` Andrew Morton
2018-09-26 0:55 ` David Rientjes
2018-09-26 6:06 ` Michal Hocko
2018-10-02 11:28 ` [RFC PATCH] mm, proc: report PR_SET_THP_DISABLE in proc Michal Hocko
2018-10-02 20:29 ` David Rientjes
2018-10-03 7:36 ` Michal Hocko
2018-10-03 22:51 ` David Rientjes
2018-10-04 5:58 ` Michal Hocko
2018-10-04 9:15 ` David Rientjes
2018-10-04 9:46 ` Michal Hocko
2018-10-04 18:34 ` David Rientjes
2018-10-09 8:33 ` Michal Hocko
2018-10-15 15:03 ` Michal Hocko [this message]
2018-10-15 22:25 ` David Rientjes
2018-10-16 10:48 ` Michal Hocko
2018-10-16 21:24 ` David Rientjes
2018-10-17 7:05 ` Michal Hocko
2018-10-17 19:59 ` David Rientjes
2018-10-18 7:00 ` Michal Hocko
2018-11-14 13:23 ` Michal Hocko
2018-11-14 21:41 ` David Rientjes
2018-11-15 9:02 ` Michal Hocko
2018-11-15 9:22 ` Michal Hocko
2018-11-19 22:05 ` David Rientjes
2018-11-20 7:48 ` Michal Hocko
2018-10-03 17:33 ` Mike Rapoport
2018-09-25 21:50 ` [patch v3] mm, thp: always specify disabled vmas as nh in smaps David Rientjes
2018-09-26 6:12 ` Michal Hocko
2018-09-26 7:17 ` Michal Hocko
2018-09-26 8:40 ` Vlastimil Babka
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