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Miller" , Jakub Kicinski , Paolo Abeni , Andrew Morton , willy@infradead.org Subject: Re: [PATCH RFC net-next/mm V1 2/3] page_pool: Use static_key for shutdown phase Message-ID: <20230425233027.w3olphld4nkcdvry@dhcp-172-26-102-232.dhcp.thefacebook.com> References: <168244288038.1741095.1092368365531131826.stgit@firesoul> <168244294384.1741095.6037010854411310099.stgit@firesoul> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <168244294384.1741095.6037010854411310099.stgit@firesoul> X-Rspam-User: X-Rspamd-Queue-Id: 34CF11C0006 X-Rspamd-Server: rspam01 X-Stat-Signature: 4n7q4qg4k3h8co895pjmd6farim3jai3 X-HE-Tag: 1682465432-357844 X-HE-Meta: U2FsdGVkX19BFr3IYb3bG63rGhH32OsyJQ+CsA6lPvNxorE7u7mbJfga2AG9+VuoQnGwgQNnR00uKJ1wlVX3yPO3HaLAmz6W886G/+Vq/DfoU2XJi2FVP2tFAp9YwnM5VWJjge6BWXCzFUcyjZolxEgeSJEwsEO4xoLfRCZaheAeQ1cD04JjscZLeOU2/0wV5Itbrp6hZ7ZQTuUjsTUBoX7Wvdvu+odoiM1Gbh1xRUq5utIP4MT4JxlowuoMcFtSviejqlJjNyWiVAgbxacSrnFMc4KQdLn7BD2cVSz0hiL/gF2O8x6QUqE42OqG7Z/y8bG9yMjho5G8ux4CPxeVW7pHwphGEc3hVo9w4+T0/M2KGncoiwaSJJ8oUYvGIvmqn9EeumfXlKgvXVOX8LLJvYUld4eQ8o3iCAHVV3qseO2lDbccOjAa3pDLenlRi1VE5v509JpRJluNXlLLvt9FiQzLThvkpfCJixjYp+2HdqF5+BY5ILW2hj9MuRia8QLcG0/VM6PWPaUh6m0RUCA9oC+hJ+yx4+CMYTrken95jcrCR/sTVkuhpQ7RQDRAjUTWDJDX1DGKGU5jISLOQte/IjOie9wo/rZ2h7sT4UmuDfnju2PLqbRRNoqmMt3zsOyt9OPUVjwQZYr2j0isvDXz0ObxBmDUiY6pYYqyFm1IIClcJn1OoVu95ZQfkt5R/H1pQ9hCruvr812wnPU9hn0l/r44NGoF6iRIq9aLuhqzv1zLvgS+pAnFfCOAw4j8zQ0w2yXT+5Int3n3DFPCjUOGkwKVifyT8QK62jX7HhmnlYHkFuPvGnJsNHenzEOm8iIlZ0VWUw8h91rR5BTU2PJ26UX6Ock+qjN2y/IMqGSH+UUa+RTFPsmk+K9+p2Tz91LTHZDSgvC30GxV0ZRqRoaGbKZwi6UmNJVEfrQXjObc8NUXEbFmMZ0H2PVjHoVwR/nNcNP40RvDH3mLXRdxhkH YVqR0zxm 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 25, 2023 at 07:15:43PM +0200, Jesper Dangaard Brouer wrote: > Performance is very important for page pool (PP). This add the use of > static_key APIs for regaining a single instruction, which makes the > new PP shutdown scheme zero impact. > > We are uncertain if this is 100% correct, because static_key APIs uses > a mutex lock and it is uncertain if all contexts that can return pages > can support this. We could spawn a workqueue (like we just removed) to > workaround this issue. With debug atomic sleep the issue should be trivial to see. iirc the callers of xdp_flush_frame_bulk() need to do it under rcu_read_lock equivalent, which is not sleepable and mutex-es should warn.