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From: Peter Zijlstra <peterz@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: "John Hubbard" <jhubbard@nvidia.com>,
	"Michal Hocko" <mhocko@kernel.org>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	"Yu Zhao" <yuzhao@google.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Arnaldo Carvalho de Melo" <acme@kernel.org>,
	"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
	"Jiri Olsa" <jolsa@redhat.com>,
	"Namhyung Kim" <namhyung@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Hugh Dickins" <hughd@google.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Andrea Arcangeli" <aarcange@redhat.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
	"David Rientjes" <rientjes@google.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Lance Roy" <ldr709@gmail.com>,
	"Ralph Campbell" <rcampbell@nvidia.com>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Dave Airlie" <airlied@redhat.com>,
	"Thomas Hellstrom" <thellstrom@vmware.com>,
	"Souptick Joarder" <jrdr.linux@gmail.com>,
	"Mel Gorman" <mgorman@suse.de>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Huang Ying" <ying.huang@intel.com>,
	"Aaron Lu" <ziqian.lzq@antfin.com>,
	"Omar Sandoval" <osandov@fb.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Vineeth Remanan Pillai" <vpillai@digitalocean.com>,
	"Daniel Jordan" <daniel.m.jordan@oracle.com>,
	"Mike Rapoport" <rppt@linux.ibm.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Alexander Duyck" <alexander.h.duyck@linux.intel.com>,
	"Pavel Tatashin" <pavel.tatashin@microsoft.com>,
	"David Hildenbrand" <david@redhat.com>,
	"Juergen Gross" <jgross@suse.com>,
	"Anthony Yznaga" <anthony.yznaga@oracle.com>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 3/4] mm: don't expose non-hugetlb page to fast gup prematurely
Date: Tue, 1 Oct 2019 10:36:04 +0200	[thread overview]
Message-ID: <20191001083604.GM4519@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191001071008.GA25062@quack2.suse.cz>

On Tue, Oct 01, 2019 at 09:10:08AM +0200, Jan Kara wrote:
> On Mon 30-09-19 10:57:08, John Hubbard wrote:

> > Well, a couple of questions:
> > 
> > 1. Is there *really* a memory barrier in try_get_compound_head()? Because
> > I only see a READ_ONCE compile barrier, which would mean that run time
> > reordering is still possible.
> 
> try_get_compound_head() has page_cache_add_speculative() which is
> atomic_add_unless() which is guaranteed to provide ordering.

atomic_add_unless() only provides ordering on SUCCESS, now looking at
the code in question that seems sufficient, so all should be well. Just
wanted to let you know that if atomic_add_unless() FAILs there is no
implied ordering what so ever.


  reply	other threads:[~2019-10-01  8:36 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-08 22:56 [PATCH] mm: don't expose page to fast gup before it's ready Yu Zhao
2018-01-08 22:56 ` Yu Zhao
2018-01-09  8:46 ` Michal Hocko
2018-01-09  8:46   ` Michal Hocko
2018-01-09 10:10   ` Yu Zhao
2018-01-09 10:10     ` Yu Zhao
2018-01-31 23:07     ` Andrew Morton
2018-01-31 23:07       ` Andrew Morton
2019-05-14 21:25     ` Andrew Morton
2019-05-14 23:07       ` Yu Zhao
2019-09-14  7:05         ` [PATCH v2] mm: don't expose page to fast gup prematurely Yu Zhao
2019-09-24 11:23           ` Kirill A. Shutemov
2019-09-24 22:05             ` Yu Zhao
2019-09-25 12:17               ` Kirill A. Shutemov
2019-09-26  3:58                 ` Yu Zhao
2019-09-24 23:24           ` [PATCH v3 1/4] mm: remove unnecessary smp_wmb() in collapse_huge_page() Yu Zhao
2019-09-24 23:24             ` Yu Zhao
2019-09-24 23:24             ` [PATCH v3 2/4] mm: don't expose hugetlb page to fast gup prematurely Yu Zhao
2019-09-24 23:24               ` Yu Zhao
2019-09-24 23:24             ` [PATCH v3 3/4] mm: don't expose non-hugetlb " Yu Zhao
2019-09-24 23:24               ` Yu Zhao
2019-09-25  8:25               ` Peter Zijlstra
2019-09-25 22:26                 ` Yu Zhao
2019-09-26 10:20                   ` Kirill A. Shutemov
2019-09-27  3:26                     ` John Hubbard
2019-09-27  5:06                       ` Yu Zhao
2019-10-01 22:31                         ` John Hubbard
2019-10-02  0:00                           ` Yu Zhao
2019-09-27 12:33                       ` Michal Hocko
2019-09-27 18:31                         ` Yu Zhao
2019-09-27 19:31                         ` John Hubbard
2019-09-29 22:47                           ` John Hubbard
2019-09-30  9:20                           ` Jan Kara
2019-09-30 17:57                             ` John Hubbard
2019-10-01  7:10                               ` Jan Kara
2019-10-01  8:36                                 ` Peter Zijlstra [this message]
2019-10-01  8:40                                   ` Jan Kara
2019-10-01 18:43                                 ` John Hubbard
2019-10-02  9:24                                   ` Jan Kara
2019-10-02 17:33                                     ` John Hubbard
2019-09-24 23:24             ` [PATCH v3 4/4] mm: remove unnecessary smp_wmb() in __SetPageUptodate() Yu Zhao
2019-09-24 23:24               ` Yu Zhao
2019-09-24 23:50               ` Matthew Wilcox
2019-09-25 22:03                 ` Yu Zhao

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