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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id j15-20020a05622a038f00b00410a9dd3d88sm3671836qtx.68.2023.10.30.13.15.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Oct 2023 13:15:35 -0700 (PDT) Date: Mon, 30 Oct 2023 16:15:13 -0400 From: Peter Xu To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, david@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v4 1/5] mm/rmap: support move to different root anon_vma in folio_move_anon_rmap() Message-ID: References: <20231028003819.652322-1-surenb@google.com> <20231028003819.652322-2-surenb@google.com> MIME-Version: 1.0 In-Reply-To: <20231028003819.652322-2-surenb@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 6FE3480020 X-Stat-Signature: kbhq8zjnjmo89z5okwte4hm1eynhkhta X-HE-Tag: 1698696939-407936 X-HE-Meta: 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 gj8iE1Uq dsqW2lm0+ijeUHcyM7pYj06B8GNvb6nU12YVE3mJGcmwwVDf2p5fEj8ROSQk7j5K38ZhQfTOrV9u+4nUQjlUsnEZyH3dVappjoZNX3lofo6WLOMAYlDZxvC1CKnzaYXdfwjJiRe45ZYa1flyA9tM7EC++sZAPfl8Qso96nlM9PlYKWpDD+uTaZL1+Vglr3SKfcaPrkD0EXurwOT4blaKapN5KwtodKH1sc2ElROmC1ihRmCamMs6MRom+d081r0WjUpqMGEHSEhr/BDWDoL0TSdMFbf1zsXdvAGnv81Z5t5K00yNac7E/Xd8pD+V1h6ONWD5F0uBrnj8k0ew1w6tSB+ibt8DZ2z98RBtWV0OW2qW4Mf8YY2i82MQ6LftgKa7rW1u+VmPJY5D5HGIFt+Ge+d+pBwZoE3kn+yDgFIVNUqi/0IPf2xcs8+ZyRS5vO+Mi/1aVe0h2Ka7OZOo= 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: List-Subscribe: List-Unsubscribe: On Fri, Oct 27, 2023 at 05:38:11PM -0700, Suren Baghdasaryan wrote: > From: Andrea Arcangeli > > For now, folio_move_anon_rmap() was only used to move a folio to a > different anon_vma after fork(), whereby the root anon_vma stayed > unchanged. For that, it was sufficient to hold the folio lock when > calling folio_move_anon_rmap(). > > However, we want to make use of folio_move_anon_rmap() to move folios > between VMAs that have a different root anon_vma. As folio_referenced() > performs an RMAP walk without holding the folio lock but only holding the > anon_vma in read mode, holding the folio lock is insufficient. > > When moving to an anon_vma with a different root anon_vma, we'll have to > hold both, the folio lock and the anon_vma lock in write mode. > Consequently, whenever we succeeded in folio_lock_anon_vma_read() to > read-lock the anon_vma, we have to re-check if the mapping was changed > in the meantime. If that was the case, we have to retry. > > Note that folio_move_anon_rmap() must only be called if the anon page is > exclusive to a process, and must not be called on KSM folios. > > This is a preparation for UFFDIO_MOVE, which will hold the folio lock, > the anon_vma lock in write mode, and the mmap_lock in read mode. > > Signed-off-by: Andrea Arcangeli > Signed-off-by: Suren Baghdasaryan Acked-by: Peter Xu -- Peter Xu