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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: [patch v2] mm, thp: always specify ineligible vmas as nh in smaps
Date: Mon, 24 Sep 2018 22:02:58 +0200	[thread overview]
Message-ID: <20180924200258.GK18685@dhcp22.suse.cz> (raw)
In-Reply-To: <20180924195603.GJ18685@dhcp22.suse.cz>

On Mon 24-09-18 21:56:03, Michal Hocko wrote:
> On Mon 24-09-18 12:30:07, David Rientjes wrote:
> > Commit 1860033237d4 ("mm: make PR_SET_THP_DISABLE immediately active")
> > introduced a regression in that userspace cannot always determine the set
> > of vmas where thp is ineligible.
> > 
> > Userspace relies on the "nh" flag being emitted as part of /proc/pid/smaps
> > to determine if a vma is eligible to be backed by hugepages.
> 
> I was under impression that nh resp hg flags only tell about the madvise
> status. How do you exactly use these flags in an application?
> 
> Your eligible rules as defined here:
> 
> > + [*] A process mapping is eligible to be backed by transparent hugepages (thp)
> > +     depending on system-wide settings and the mapping itself.  See
> > +     Documentation/admin-guide/mm/transhuge.rst for default behavior.  If a
> > +     mapping has a flag of "nh", it is not eligible to be backed by hugepages
> > +     in any condition, either because of prctl(PR_SET_THP_DISABLE) or
> > +     madvise(MADV_NOHUGEPAGE).  PR_SET_THP_DISABLE takes precedence over any
> > +     MADV_HUGEPAGE.
> 
> doesn't seem to match the reality. I do not see all the file backed
> mappings to be nh marked. So is this really about eligibility rather
> than the madvise status? Maybe it is just the above documentation that
> needs to be updated.
> 
> That being said, I do not object to the patch, I am just trying to
> understand what is the intended usage for the flag that does try to say
> more than the madvise status.

And moreover, how is the PR_SET_THP_DISABLE any different from the
global THP disabled case. Do we want to set all vmas to nh as well?
-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2018-09-24 20:03 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 [this message]
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
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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