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[2003:cb:c704:1100:65a0:c03a:142a:f914]) by smtp.gmail.com with ESMTPSA id az22-20020adfe196000000b002bddaea7a0bsm26589755wrb.57.2023.01.23.04.59.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jan 2023 04:59:56 -0800 (PST) Message-ID: <3e431c82-189a-f82c-6545-b8bd441cce52@redhat.com> Date: Mon, 23 Jan 2023 13:59:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 To: Jason Gunthorpe Cc: Alistair Popple , John Hubbard , linux-mm@kvack.org References: <6-v1-dd94f8f0d5ad+716-gup_tidy_jgg@nvidia.com> <89c98586-8d38-7f30-1e7d-21a5f9ce7c89@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH 6/8] mm/gup: make locked never NULL in the internal GUP functions In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: yeiim4ecgej1pigeom7qmxxcgpiwqobz X-Rspam-User: X-Rspamd-Queue-Id: 9ABD918000F X-Rspamd-Server: rspam06 X-HE-Tag: 1674478800-203511 X-HE-Meta: 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 p+Gv+Vfo 7YMTL0H2aL0Pi6nsJgnJngPQQgW6oSe249dsY9Lbui5p5ny/V1ZaKWaco3mCZ6tOxja2VWgULG0L3mq9Hco74qI1ygo2BiEzGU7ngPFbdWinp2Yge66SqMR/nrmhg88hCadLQkZlowRXJVoo+7bWmC965BlYL8Tr6xZ0iXTMraFv04QKpH9PzFFIvrJhU1LERvxlvtswHr/0Mz0SbAclmXa/6KIcCbNHYKYmQPEeeqbqgSYuQWLenDBTnX6GE0YRKOAHf1Gmzak6YymFoEi+tMpDUdimey4N//odI+HonA+Zk1kagz+3mg//u1V82LuTEbPQIPC7PafGNuPhjoEVK1nwws3QS7anBdrzHobI6C4Zu6mfjR9c/JzEt9x+WAafERKHwf36nPJDVa90TWb4IMNYnzm8GYQp2rARZNrbmuf5IA6Q= 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 23.01.23 13:44, Jason Gunthorpe wrote: > On Mon, Jan 23, 2023 at 12:35:28PM +0100, David Hildenbrand wrote: >> On 17.01.23 16:58, Jason Gunthorpe wrote: >>> Now that NULL locked doesn't have a special meaning we can just make it >>> non-NULL in all cases and remove the special tests. >>> >>> get_user_pages() and pin_user_pages() can safely pass in a locked = 1 >>> >>> get_user_pages_remote) and pin_user_pages_remote() can swap in a local >>> variable for locked if NULL is passed. >>> >>> Remove all the NULL checks. >>> >>> Signed-off-by: Jason Gunthorpe >>> --- >>> mm/gup.c | 30 ++++++++++++++++++++---------- >>> 1 file changed, 20 insertions(+), 10 deletions(-) >> >> ... doesn't really look like a real cleanup. Especially with the >> >> 2 files changed, 20 insertions(+), 12 deletions(-) >> >> on the previous patch and a new internal flag .... >> >> What's the benefit? > > There are all kinds of unnecessary branches on the faster paths, > inside loops, etc to check for NULL when all we really needed was a > single bit flag. ... call me skeptical that this optimization matters in practice ;) > > It isalos much clearer to understand that a FOLL flag changes the > behavior of how GUP works rather than some weirdo NULL argument. The whole "locked" parameter handling is weird. I don't think adding a new FOLL_ internal flag on top particularly improves the situation ... at least before, the logic around that "locked" parameter handling was self-contained. Self-contained weirdness. -- Thanks, David / dhildenb