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Wed, 24 May 2023 15:55:35 -0700 (PDT) MIME-Version: 1.0 References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> <34467cca-58b6-3e64-1ee7-e3dc43257a@google.com> In-Reply-To: <34467cca-58b6-3e64-1ee7-e3dc43257a@google.com> From: Yu Zhao Date: Wed, 24 May 2023 16:54:59 -0600 Message-ID: Subject: Re: [PATCH 01/31] mm: use pmdp_get_lockless() without surplus barrier() To: Hugh Dickins Cc: Andrew Morton , Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: z4m7zbxamtuyczcbzn187nnfxg738ews X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 051FA180011 X-HE-Tag: 1684968936-666497 X-HE-Meta: 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 ENK/bUc9 g+CQLPn8YMrO39DvtD+pvBlTLt36XDLkHAqS8UbzdaOkFDcUWPzPmVBY5j5p8vnTOCAfaIenrj6VDJoAuMexI6uW3RLdxlO9jPnoRVKfSLMP01JC34QRRovqPQpfiW5dtD/ZQfw2ug/F6DxFicdm+9Boi6fuvsW9cRIoQQJNoa0BbpLfGBT4fbjOkZRbz9Iux7/i3O9VxDPlsSJ/8zlYaJF9W5/HBGYe85fm4VASeb+XOPJFpmQnthyJNAw5/n4LmLVjQwzy8WhBAqJYY/dGTQDsig0mSzXtxfnz7+SWvfFLzWAkNiMecAgSUSgSP/Z4ievInAlD6/SchP4t9PAJipZhgEStpnRWDgRND2uHRPwXlVupVIpdZf+h1Pb3TvCTnCbXm X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, May 21, 2023 at 10:49=E2=80=AFPM Hugh Dickins wr= ote: > > Use pmdp_get_lockless() in preference to READ_ONCE(*pmdp), to get a more > reliable result with PAE (or READ_ONCE as before without PAE); and remove > the unnecessary extra barrier()s which got left behind in its callers. > > HOWEVER: Note the small print in linux/pgtable.h, where it was designed > specifically for fast GUP, and depends on interrupts being disabled for > its full guarantee: most callers which have been added (here and before) > do NOT have interrupts disabled, so there is still some need for caution. > > Signed-off-by: Hugh Dickins Acked-by: Yu Zhao The previous ask here: https://lore.kernel.org/r/CAOUHufZo=3DfB2HcaCrj2aidLJ2zEhOpi7ou5M_7qOQiuQq8= +wTQ@mail.gmail.com/