From: Michal Hocko <mhocko@suse.cz>
To: Mel Gorman <mgorman@suse.de>
Cc: Linux-MM <linux-mm@kvack.org>, Hugh Dickins <hughd@google.com>,
David Gibson <david@gibson.dropbear.id.au>,
Ken Chen <kenchen@google.com>,
Cong Wang <xiyou.wangcong@gmail.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend)
Date: Fri, 20 Jul 2012 16:40:42 +0200 [thread overview]
Message-ID: <20120720144041.GG12434@tiehlicka.suse.cz> (raw)
In-Reply-To: <20120720143753.GI9222@suse.de>
On Fri 20-07-12 15:37:53, Mel Gorman wrote:
> On Fri, Jul 20, 2012 at 04:29:20PM +0200, Michal Hocko wrote:
> > > <SNIP>
> > >
> > > Signed-off-by: Mel Gorman <mgorman@suse.de>
> >
> > Yes this looks correct. mmap_sem will make sure that unmap_vmas and
> > free_pgtables are executed atomicaly wrt. huge_pmd_share so it doesn't
> > see non-NULL spte on the way out.
>
> Yes.
>
> > I am just wondering whether we need
> > the page_table_lock as well. It is not harmful but I guess we can drop
> > it because both exit_mmap and shmdt are not taking it and mmap_sem is
> > sufficient for them.
>
> While it is true that we don't *really* need page_table_lock here, we are
> still updating page tables and it's in line with the the ordinary locking
> rules. There are other cases in hugetlb.c where we do pte_same() checks even
> though we are protected from the related races by the instantiation_mutex.
>
> page_table_lock is actually a bit useless for shared page tables. If shared
> page tables were every to be a general thing then I think we'd have to
> revisit how PTE update locking is done but I doubt anyone wants to dive
> down that rat-hole.
>
> For now, I'm going to keep taking it even if strictly speaking it's not
> necessary.
Fair enough
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@suse.cz>
To: Mel Gorman <mgorman@suse.de>
Cc: Linux-MM <linux-mm@kvack.org>, Hugh Dickins <hughd@google.com>,
David Gibson <david@gibson.dropbear.id.au>,
Ken Chen <kenchen@google.com>,
Cong Wang <xiyou.wangcong@gmail.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend)
Date: Fri, 20 Jul 2012 16:40:42 +0200 [thread overview]
Message-ID: <20120720144041.GG12434@tiehlicka.suse.cz> (raw)
In-Reply-To: <20120720143753.GI9222@suse.de>
On Fri 20-07-12 15:37:53, Mel Gorman wrote:
> On Fri, Jul 20, 2012 at 04:29:20PM +0200, Michal Hocko wrote:
> > > <SNIP>
> > >
> > > Signed-off-by: Mel Gorman <mgorman@suse.de>
> >
> > Yes this looks correct. mmap_sem will make sure that unmap_vmas and
> > free_pgtables are executed atomicaly wrt. huge_pmd_share so it doesn't
> > see non-NULL spte on the way out.
>
> Yes.
>
> > I am just wondering whether we need
> > the page_table_lock as well. It is not harmful but I guess we can drop
> > it because both exit_mmap and shmdt are not taking it and mmap_sem is
> > sufficient for them.
>
> While it is true that we don't *really* need page_table_lock here, we are
> still updating page tables and it's in line with the the ordinary locking
> rules. There are other cases in hugetlb.c where we do pte_same() checks even
> though we are protected from the related races by the instantiation_mutex.
>
> page_table_lock is actually a bit useless for shared page tables. If shared
> page tables were every to be a general thing then I think we'd have to
> revisit how PTE update locking is done but I doubt anyone wants to dive
> down that rat-hole.
>
> For now, I'm going to keep taking it even if strictly speaking it's not
> necessary.
Fair enough
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
next prev parent reply other threads:[~2012-07-20 14:40 UTC|newest]
Thread overview: 100+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-20 13:49 [PATCH] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables v2 Mel Gorman
2012-07-20 13:49 ` Mel Gorman
2012-07-20 14:11 ` [PATCH] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend) Mel Gorman
2012-07-20 14:11 ` Mel Gorman
2012-07-20 14:29 ` Michal Hocko
2012-07-20 14:29 ` Michal Hocko
2012-07-20 14:37 ` Mel Gorman
2012-07-20 14:37 ` Mel Gorman
2012-07-20 14:40 ` Michal Hocko [this message]
2012-07-20 14:40 ` Michal Hocko
2012-07-20 14:36 ` [PATCH -alternative] " Michal Hocko
2012-07-20 14:36 ` Michal Hocko
2012-07-20 14:51 ` Mel Gorman
2012-07-20 14:51 ` Mel Gorman
2012-07-23 4:04 ` Hugh Dickins
2012-07-23 4:04 ` Hugh Dickins
2012-07-23 11:40 ` Mel Gorman
2012-07-23 11:40 ` Mel Gorman
2012-07-24 1:08 ` Hugh Dickins
2012-07-24 1:08 ` Hugh Dickins
2012-07-24 8:32 ` Michal Hocko
2012-07-24 8:32 ` Michal Hocko
2012-07-24 9:34 ` Mel Gorman
2012-07-24 9:34 ` Mel Gorman
2012-07-24 10:04 ` Michal Hocko
2012-07-24 10:04 ` Michal Hocko
2012-07-24 19:23 ` Hugh Dickins
2012-07-24 19:23 ` Hugh Dickins
2012-07-25 8:36 ` Mel Gorman
2012-07-25 8:36 ` Mel Gorman
2012-07-26 17:42 ` Rik van Riel
2012-07-26 17:42 ` Rik van Riel
2012-07-26 18:04 ` Larry Woodman
2012-07-26 18:04 ` Larry Woodman
2012-07-27 8:42 ` Mel Gorman
2012-07-27 8:42 ` Mel Gorman
2012-07-26 18:37 ` Rik van Riel
2012-07-26 18:37 ` Rik van Riel
2012-07-26 21:03 ` Larry Woodman
2012-07-26 21:03 ` Larry Woodman
2012-07-27 3:48 ` Larry Woodman
2012-07-27 3:48 ` Larry Woodman
2012-07-27 10:10 ` Larry Woodman
2012-07-27 10:10 ` Larry Woodman
2012-07-27 10:23 ` Mel Gorman
2012-07-27 10:23 ` Mel Gorman
2012-07-27 10:36 ` Larry Woodman
2012-07-27 10:36 ` Larry Woodman
2012-07-30 19:11 ` Larry Woodman
2012-07-30 19:11 ` Larry Woodman
2012-07-31 12:16 ` Hillf Danton
2012-07-31 12:16 ` Hillf Danton
2012-07-31 12:46 ` Mel Gorman
2012-07-31 12:46 ` Mel Gorman
2012-07-31 13:07 ` Larry Woodman
2012-07-31 13:07 ` Larry Woodman
2012-07-31 13:29 ` Mel Gorman
2012-07-31 13:29 ` Mel Gorman
2012-07-31 13:21 ` Michal Hocko
2012-07-31 13:21 ` Michal Hocko
2012-07-31 17:49 ` Larry Woodman
2012-07-31 17:49 ` Larry Woodman
2012-07-31 20:06 ` Michal Hocko
2012-07-31 20:06 ` Michal Hocko
2012-07-31 20:57 ` Larry Woodman
2012-07-31 20:57 ` Larry Woodman
2012-08-01 2:45 ` Larry Woodman
2012-08-01 2:45 ` Larry Woodman
2012-08-01 8:20 ` Michal Hocko
2012-08-01 8:20 ` Michal Hocko
2012-08-01 12:32 ` Michal Hocko
2012-08-01 12:32 ` Michal Hocko
2012-08-01 15:06 ` Larry Woodman
2012-08-01 15:06 ` Larry Woodman
2012-08-02 7:19 ` Michal Hocko
2012-08-02 7:19 ` Michal Hocko
2012-08-02 7:37 ` Mel Gorman
2012-08-02 7:37 ` Mel Gorman
2012-08-02 12:36 ` Michal Hocko
2012-08-02 12:36 ` Michal Hocko
2012-08-02 13:33 ` Mel Gorman
2012-08-02 13:33 ` Mel Gorman
2012-08-02 13:53 ` Michal Hocko
2012-08-02 13:53 ` Michal Hocko
2012-07-31 18:03 ` Rik van Riel
2012-07-31 18:03 ` Rik van Riel
2012-07-26 18:31 ` Rik van Riel
2012-07-26 18:31 ` Rik van Riel
2012-07-27 9:02 ` Michal Hocko
2012-07-27 9:02 ` Michal Hocko
2012-07-26 16:01 ` [PATCH] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables v2 Larry Woodman
2012-07-26 16:01 ` Larry Woodman
2012-07-27 8:47 ` Mel Gorman
2012-07-27 8:47 ` Mel Gorman
2012-07-26 21:00 ` Rik van Riel
2012-07-26 21:00 ` Rik van Riel
2012-07-26 21:54 ` Hugh Dickins
2012-07-26 21:54 ` Hugh Dickins
2012-07-27 8:52 ` Mel Gorman
2012-07-27 8:52 ` Mel Gorman
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