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Mon, 31 Jul 2023 05:39:16 -0700 (PDT) Received: from [10.90.34.137] ([203.208.167.147]) by smtp.gmail.com with ESMTPSA id q16-20020a170902dad000b001b89c313185sm8505332plx.205.2023.07.31.05.39.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 31 Jul 2023 05:39:15 -0700 (PDT) Message-ID: <20aab1af-c183-db94-90d7-5e5425e3fd80@bytedance.com> Date: Mon, 31 Jul 2023 20:39:08 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.13.1 Subject: Re: [PATCH 06/11] maple_tree: Introduce mas_replace_entry() to directly replace an entry To: "Liam R. Howlett" References: <20230726080916.17454-1-zhangpeng.00@bytedance.com> <20230726080916.17454-7-zhangpeng.00@bytedance.com> <20230726160843.hpl4razxiikqbuxy@revolver> Cc: Peng Zhang , avagin@gmail.com, npiggin@gmail.com, mathieu.desnoyers@efficios.com, peterz@infradead.org, michael.christie@oracle.com, surenb@google.com, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, corbet@lwn.net, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org From: Peng Zhang In-Reply-To: <20230726160843.hpl4razxiikqbuxy@revolver> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 66A4440018 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: czpe7p13s4nz8y7ok9mnm4ro7z7bb7xw X-HE-Tag: 1690807157-894937 X-HE-Meta: U2FsdGVkX19nPELm+siZqH5Ah6FpJ2n0CxaDyfEB3duhhTmqFR4rSw5NGOH1iWoJuhH+Rmbct4zYafGWRSv6jgcDYZCUXH7zTB0VUB1mhtrSHI1C6sh0KNxEfGyL4MopM6YTUtIgxNkZWAsZEA2w/cGRoLYptJaXN2ubzATa2iYPg7nPBPHU4SsMMGKTLMypgffe3EYqOsSYRKu910EFM+dpa91fOljzG1ArNexI+UZCb65ki0Uod8mELpx3Crtl4XQwGjnJt//27t8NV51J0/Q6QCRoFZXoWwLp7kbD+0WVaBpUxL3yFInfJjX6r4+ze7L3Xqlsos30uUgMzDdEw2Luawx12JPJeV2GigBXsu5XALKRVEk0kc+djMAPqjx2n6TojGmVBbOHmSpqT3KDh7KAN07KtOhD3BqsV32A5xtC1lsOJO757NEfKt7nnHA7ScJffUO1vRg9prNpRbZMvZU1cQGs5pFNW/X6lar2/4GLtZwdB5v0FzxD/IzmWMdTq8VKB83zaheDwDlgaH2GjLHUrSVG66T9SYLbSamIO/AMgYPikHFe78IP6wKihzTXdJ91ZSOyrQW3wU6/T3MtsuZOI2gqm5W4YH7J6PNTCejQ9hFhQFHwLnpM04CnpSOsOie2wBPR4884zLV2P95cyE++l93j5wCAkQHza3Zov+5/uRBRlaaWyg5dxKw97Gc4HYv3nFt0zOH5SbDhcHR7Aq1IwMoQ+DtWZQ30IVqcTPwvO8jw2LnL4S5zvLayY0zwyCNHCpi2M4z3FyX61USqNtAGbCIaQUjMSFh9h6ksS5ulY4YtrDyySoBm8byTjwfO+tJFiiotg6ANlIvA1RYsqzfOnW084aJZfpPa2gjSGgGsPvTp4dNViL6vkX5IZDoIMW6ie9/XoFn8olyA7YDqO2te6VW0BtIVQfHRmb8hZOJJ4W8nKZjMcPhztjzUuF9h0ahaMme1Ot3+WvMDs7v syvfqBF6 2WmTREMIqVPiCSq+wcmXUmb1HBnQhokd4ayJpm3xPuEN1QdwfNUrMVY7kpDD9sjJHz/fMudSXodvNTaNnVNaoxUDZC02xlQvVUKMg95/IcCNK8TBT6Sb2TR5HXLVLirB5dRvJEo98HvYowV4VOT16Ff+jccSB+WjdzCBLWJkYaofn6TsMqZjyNML2d4nslWbUW+0Nkp84bsW33c4pQfg2L3iXk7hAYDu389TBy+zqW0z71ucGWqUZ1JtaUsXSJdSKYzElh2nbJFILhxAoeGymBU9zSldq8huc4YXTNIRzP1DFiZ3cRf/sO7YtHL5TRlzRQjFuWQaW7EYGYK04CO1Opaa2Ue5q0hhJ9Rz9uILbXSHBTAWPkszKyaBLhpQFBWHN9vSEAdo/UsBnrdBGSqzitANv8SwuHbuTGfucedFWEs1XwczuiKM0Q9r2TETRXB0KsVzRZbWU8gdHc9D6OSRanYLjE9xMYlJbYU2I X-Bogosity: Ham, tests=bogofilter, spamicity=0.000064, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 在 2023/7/27 00:08, Liam R. Howlett 写道: > * Peng Zhang [230726 04:10]: >> If mas has located a specific entry, it may be need to replace this >> entry, so introduce mas_replace_entry() to do this. mas_replace_entry() >> will be more efficient than mas_store*() because it doesn't do many >> unnecessary checks. >> >> This function should be inline, but more functions need to be moved to >> the header file, so I didn't do it for the time being. > > I am really nervous having no checks here. I get that this could be > used for duplicating the tree more efficiently, but having a function > that just swaps a value in is very dangerous - especially since it is > decoupled from the tree duplication code. I've thought about this, and I feel like this is something the user should be guaranteed. If the user is not sure whether to use it, mas_store() can be used instead. And we should provide this interface because it has better performance. > >> >> Signed-off-by: Peng Zhang >> --- >> include/linux/maple_tree.h | 1 + >> lib/maple_tree.c | 25 +++++++++++++++++++++++++ >> 2 files changed, 26 insertions(+) >> >> diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h >> index 229fe78e4c89..a05e9827d761 100644 >> --- a/include/linux/maple_tree.h >> +++ b/include/linux/maple_tree.h >> @@ -462,6 +462,7 @@ struct ma_wr_state { >> >> void *mas_walk(struct ma_state *mas); >> void *mas_store(struct ma_state *mas, void *entry); >> +void mas_replace_entry(struct ma_state *mas, void *entry); >> void *mas_erase(struct ma_state *mas); >> int mas_store_gfp(struct ma_state *mas, void *entry, gfp_t gfp); >> void mas_store_prealloc(struct ma_state *mas, void *entry); >> diff --git a/lib/maple_tree.c b/lib/maple_tree.c >> index efac6761ae37..d58572666a00 100644 >> --- a/lib/maple_tree.c >> +++ b/lib/maple_tree.c >> @@ -5600,6 +5600,31 @@ void *mas_store(struct ma_state *mas, void *entry) >> } >> EXPORT_SYMBOL_GPL(mas_store); >> >> +/** >> + * mas_replace_entry() - Replace an entry that already exists in the maple tree >> + * @mas: The maple state >> + * @entry: The entry to store >> + * >> + * Please note that mas must already locate an existing entry, and the new entry >> + * must not be NULL. If these two points cannot be guaranteed, please use >> + * mas_store*() instead, otherwise it will cause an internal error in the maple >> + * tree. This function does not need to allocate memory, so it must succeed. >> + */ >> +void mas_replace_entry(struct ma_state *mas, void *entry) >> +{ >> + void __rcu **slots; >> + >> +#ifdef CONFIG_DEBUG_MAPLE_TREE >> + MAS_WARN_ON(mas, !mte_is_leaf(mas->node)); >> + MAS_WARN_ON(mas, !entry); >> + MAS_WARN_ON(mas, mas->offset >= mt_slots[mte_node_type(mas->node)]); >> +#endif >> + >> + slots = ma_slots(mte_to_node(mas->node), mte_node_type(mas->node)); >> + rcu_assign_pointer(slots[mas->offset], entry); >> +} >> +EXPORT_SYMBOL_GPL(mas_replace_entry); >> + >> /** >> * mas_store_gfp() - Store a value into the tree. >> * @mas: The maple state >> -- >> 2.20.1 >>