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bh=IS6HJYpOFVi4CPNNzsDzDEh+FBChpu2Srs6gQMB3T7c=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=xdl9dDNiVfKw9plbtOCSZ3wgAXFIUPm0+vCYThT9kkVXydC3Lpt4rCbsKFSpmh5J6 xhw22O9gnJ3RCXD8MMY2pf3uVqv2FVCAMMyU94nKeibSdmQ1nrUKmVGl402SKKokDs C4VaPgO8KEB+Pk7caieUiDgaDjEAhyGy9DYMnZ7o= Date: Fri, 27 Jan 2023 14:51:38 -0800 From: Andrew Morton To: Suren Baghdasaryan Cc: michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, rppt@kernel.org, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v2 00/33] Per-VMA locks Message-Id: <20230127145138.8cc44bf00ebf289dffec0975@linux-foundation.org> In-Reply-To: <20230127194110.533103-1-surenb@google.com> References: <20230127194110.533103-1-surenb@google.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 96990140010 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: 3ng9o69rst8tck1c6mcjrjysg4xweris X-HE-Tag: 1674859902-568148 X-HE-Meta: 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 IVc8Glpo NjQxCSMB+VxwoaAHmObcJ3eoW+q9lkQNmx7pr+BmQyRX+lMyMjciNfBPaglPDyi2/9TrsQAADPYFt8JR3EU1jB5/hSl8xzcAvs3YZmNpEbw5OONFCILDY/NaUVock2Em3ktMFV/RPSA46sAeaHOQJx4aNiYDDA8JWEB5WRh6FEQfB9GL3WLHjHYuBXPT8QY4zUG9UYUk6oRFllINyAnNEDLbIsGYki0wEyscgrexw9hGYO17V/X0ao9gHIBSuXQ4+3u6lpGSnMfXGzkk2qFw4ojXBqBj0iN4GJXAS5NCTaeLm9brzzugwOxnFU5m67daNg6+cJBXrxIkc/8gF3XRyYzHD9hqAQO1x+1dV4QQUsT2sEdjuzsA0mvx8Kw== 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 Fri, 27 Jan 2023 11:40:37 -0800 Suren Baghdasaryan wrote: > Per-vma locks idea that was discussed during SPF [1] discussion at LSF/MM > last year [2], which concluded with suggestion that “a reader/writer > semaphore could be put into the VMA itself; that would have the effect of > using the VMA as a sort of range lock. There would still be contention at > the VMA level, but it would be an improvement.” This patchset implements > this suggested approach. I think I'll await reviewer/tester input for a while. > The patchset implements per-VMA locking only for anonymous pages which > are not in swap and avoids userfaultfs as their implementation is more > complex. Additional support for file-back page faults, swapped and user > pages can be added incrementally. This is a significant risk. How can we be confident that these as yet unimplemented parts are implementable and that the result will be good?