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Thu, 23 Feb 2023 06:51:40 -0800 (PST) Date: Thu, 23 Feb 2023 14:51:27 +0000 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> 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, 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, 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 16/35] mm/mmap: write-lock VMAs before merging, splitting or expanding them Message-ID: References: <20230216051750.3125598-1-surenb@google.com> <20230216051750.3125598-17-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230216051750.3125598-17-surenb@google.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6FFBE40007 X-Stat-Signature: z3z5gx1to8sutfgcdsw7nsdphazxpyqi X-HE-Tag: 1677163903-869412 X-HE-Meta: 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 tKrZYJJY YlPhhz7ztaORQuVoFYYE0iEw7B95HFj2PuQfJDodSKhI41bQw2nPEu8m+N7+a99gXqBzhAVu3nPGD/qLbeETfx/mB6c6hJwVnYMkfIvQTRDhW8IteihTp5It81CfmqK4m8we1V4FcmQFePS+WdGHgvD8vd+11a9fTvsmneQCbz/9RHjJIjGRNVKqf/WP1C7JmGUj7+O5Xj/nvmrD22dmxzrb3eUfFN7im3yUur19v5oDNeFJvdq6+f0Joy1Sbj9S7ahTr1uaP0G0FoHjrEMfY/3eAQwE+pKwryzuRA78hFDqgd9R7ZsjgyT2AACe1WFOSw2DxOROUWd9Al8YhcHjLZpTkainOawJ13CJ+g1osiIMHgewh1TqkboelnPIyOw8BJr1l17m6WlIFX+e4DnCL1gKpY7eOUmrhkvOGuXAJZksjP8kDHoUy4uhith4UXOjQNf5sCR/FXbktSCQ= 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 09:17:31PM -0800, Suren Baghdasaryan wrote: > Decisions about whether VMAs can be merged, split or expanded must be > made while VMAs are protected from the changes which can affect that > decision. For example, merge_vma uses vma->anon_vma in its decision Did you mean vma_merge()? > whether the VMA can be merged. Meanwhile, page fault handler changes > vma->anon_vma during COW operation. > Write-lock all VMAs which might be affected by a merge or split operation > before making decision how such operations should be performed. > It doesn't make sense (to me) to update vma->anon_vma during COW fault. AFAIK children's vma->anon_vma is allocated during fork() and page->anon_vma is updated on COW to reduce rmap walking because it's now unshared, no? As patch 26 just falls back to mmap_lock if no anon_vma is set, I think we can assume nothing updates vma->anon_vma (and its interval tree) if we are holding mmap_lock in write mode. Or am I missing something? -- Regards, Hyeonggon