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 21:56:03 +0200 [thread overview]
Message-ID: <20180924195603.GJ18685@dhcp22.suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.21.1809241227370.241621@chino.kir.corp.google.com>
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.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-09-24 19:56 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 [this message]
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
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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