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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pSgRD-008WXZ-IG; Thu, 16 Feb 2023 15:44:47 +0000 Date: Thu, 16 Feb 2023 15:44:47 +0000 From: Matthew Wilcox To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, 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, 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, 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, gurua@google.com, arjunroy@google.com, soheil@google.com, leewalsh@google.com, posk@google.com, michalechner92@googlemail.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 v3 26/35] mm: fall back to mmap_lock if vma->anon_vma is not yet set Message-ID: References: <20230216051750.3125598-1-surenb@google.com> <20230216051750.3125598-27-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230216051750.3125598-27-surenb@google.com> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 16F781C0025 X-Stat-Signature: pih5yc4k9cstedpqtcjfr4g9moqmyort X-HE-Tag: 1676562339-979838 X-HE-Meta: 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 16mmZKEf JSC2iE7kFo6wDbINnE68z3JhUoEJFON1cPO8dPcgUfUmSvl0ItbFyEM8xjXH4vqoK5WNcB+JVxOcG82tIvy+yqtuscYxeagBhU4xqmXF3BwyxyWQDmd8oamAuasFXxn4VCY10SF9T5k5N7cTw4qP63tyteGHsc7kls1bsdo5Uv5YAppkj1UoIDd8W2qZkr1A+YUqrv3LxXnlkTFw= 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, Feb 15, 2023 at 09:17:41PM -0800, Suren Baghdasaryan wrote: > When vma->anon_vma is not set, page fault handler will set it by either > reusing anon_vma of an adjacent VMA if VMAs are compatible or by > allocating a new one. find_mergeable_anon_vma() walks VMA tree to find > a compatible adjacent VMA and that requires not only the faulting VMA > to be stable but also the tree structure and other VMAs inside that tree. > Therefore locking just the faulting VMA is not enough for this search. > Fall back to taking mmap_lock when vma->anon_vma is not set. This > situation happens only on the first page fault and should not affect > overall performance. I think I asked this before, but don't remember getting an aswer. Why do we defer setting anon_vma to the first fault? Why don't we set it up at mmap time?