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
next prev parent 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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