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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id ci7-20020a05622a260700b00401e22b9fcesm11824110qtb.53.2023.07.05.14.55.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Jul 2023 14:55:49 -0700 (PDT) Date: Wed, 5 Jul 2023 17:55:47 -0400 From: Peter Xu To: Matthew Wilcox Cc: Suren Baghdasaryan , David Hildenbrand , akpm@linux-foundation.org, jirislaby@kernel.org, jacobly.alt@gmail.com, holger@applied-asynchrony.com, hdegoede@redhat.com, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, 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, 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, chriscli@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, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v3 2/2] mm: disable CONFIG_PER_VMA_LOCK until its fixed Message-ID: References: <20230705171213.2843068-1-surenb@google.com> <20230705171213.2843068-3-surenb@google.com> <3cdaa7d4-1293-3806-05ce-6b7fc4382458@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: AAF9214000F X-Rspam-User: X-Stat-Signature: ni5zeq85cmkx3nz5nfg554q6oyypjhxj X-Rspamd-Server: rspam01 X-HE-Tag: 1688594152-32136 X-HE-Meta: U2FsdGVkX18Y/U9MJbWh0ZNcdsEwSyXzCw2B0S66+/Ms5OrkorglPrM+YA2PVh5a54sJI5qUQp1YXcIAp4Xj9tciuTryBDRGegevuDB2rnLv9LiMc1nbPq8oPPAnhBBh0thVDC8Fp23O4+QiYHbricj8iD1kTR8kajKWhrCU3akjDNw/uh58MpfWsg655NlxFM6P4x7dtPRbNYrAXlF8t/Xz02Ht93xb/ZX98yTA8bq2pbdQkZtqy6GA+TgjstnUpfTY65BokWhSQDJv9GNoe4nE6PRo4p+5bAQuIEmV9OCr1E3wYD5rkYmx4/NcPu/zTwPYQxf135kK2OdJGknaeR6XDMPFYRftRHRY+7Sc6PQ/C+MKk3GysimpR1MN+1fF8qBJE+pjAKvPjD1LZyN/DMGukcbmjTxA2VyHPQ2nL1cR0NQ9QNDy5XhjX4uq1O1I+iJWtn7x1qw9F9XFzC3KSVPOFE79cmsdRWHX7KEpE974SAwPqj3I7CMM0ACqrZ58T31yNk3y5XX7C2N0jTxVZ9EtWsNehYJqSbnqrSmxA5tT8AlNLWBin16JMZUYanktt5UMrTewq2WkIwSwdhRLSD1VQpSVN+g05gpgNyhLhCNKGsb/Vjk5nEAcbStW5M3DkCOdeut9jPovq8xYvgkc9R4EpTHqlTGsDP5Vc8yBTsybdZfaTxYDqCZ7hMwKi5oYRkhuSbVUcOOmbdqXMXGmuUnsgjhnoMZ//0hUTcd7U6Lj+hb1rwKvrCjVS41oqeXwdCtQPCusFfrifNh1aM1kqT8XNjGhsZs669TdSa5dEh9wjjvwMcwZSCv4Dtd8yRLmDK2QI8iVK+28MCstXY/JKymo2PM1jeWUQ55ywX37IY9bvgLXM1YmzUovbnZf3POgPkpUoRqKAH/tf1OQIAUD3w5iiyMLxK7HvuSRab6qI+4DXSzD3r7chgc7xc/ItwPuTi9Cpu7bg8cm4G3FPuF syhpzPaQ XvKFZKhPPht23RhXAUhvAGl5+NOUUAMpJ5pQ9UMO9pcB6jEeIBQm3DPwDZJ5WAeF0iq+stU94ek3HqwihOeGNaEoEDWUj3grjHRxBk15JYqyfbiWJg0SWETQ4B+xiQ79DaEIbh6IvslG6yzbbfcxoAYrMIpeEyikmwQDazmNICQLENPd5mrpOzoaXjzBFZ+1tKmwX/cjJL9GdUvOh4iFbDmr69+eSA+HzwWx7DeXVEBFf2J+cG9h/JIARg7CxNS9iDeas+Ic2tAMBeRPjO9nO5dOuBh3UG7/BO6GAowCndLfR1xZH6ZupMgI7T9M2X2gZPnYnuPJALkEHZI/4nBt14y6oLj/f8BN95I9h6MN8GF5arB1JCk4VHrE8LSnvXNXsTQqX7nQKzXbc1JsPVkpdekmBj0mQi3Z0mWGBXJZjTabX1v8tgR1zrRWJ6Q+iSiBR1D+skp1efyVsGDy0gFJdBaIXvtP/jy53QHv9J7UDALxqBbA= 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 Wed, Jul 05, 2023 at 10:27:56PM +0100, Matthew Wilcox wrote: > On Wed, Jul 05, 2023 at 04:25:21PM -0400, Peter Xu wrote: > > There'll still try to be a final fix, am I right? As IIRC allowing page > > faults during fork() is one of the major goals of vma lock. > > Good grief, no. Why would we want to optimise something that happens > so rarely? The goal is, as usual, more performance. Satisfying page > faults while mmap()/munmap()/mprotect() are happening is worthwhile. > Those happen a lot more than fork(). > > In this case though, there's also a priority-inversion problem that > we're trying to solve where process A (high priority) calls mmap() while > process B (low priority) is reading /proc/$pid/smaps and now (because > rwsems are fair), none of process A's other threads can satisy any page > faults until process B is scheduled. Is it possible to extend vma lock to things like smaps? > > Where on earth did you get the idea that we cared even a little bit > about the performance of page fault during fork()? My memory, when I was talking to someone during the conference that mentioned such a use case. But my memory can be just wrong, in that case it's my fault, but I hope it's still fine to just ask here. -- Peter Xu