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Mon, 10 Jul 2023 03:58:40 -0700 (PDT) Received: from [10.90.35.114] ([203.208.167.147]) by smtp.gmail.com with ESMTPSA id u8-20020a62ed08000000b0067ab572c72fsm6919768pfh.84.2023.07.10.03.58.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 10 Jul 2023 03:58:40 -0700 (PDT) Message-ID: <8bc21e32-fdb0-e1a3-477f-dd660646ccdd@bytedance.com> Date: Mon, 10 Jul 2023 18:58:35 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH] mm: kfence: allocate kfence_metadata at runtime To: Alexander Potapenko Cc: elver@google.com, dvyukov@google.com, akpm@linux-foundation.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, muchun.song@linux.dev, Peng Zhang References: <20230710032714.26200-1-zhangpeng.00@bytedance.com> From: Peng Zhang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 54E1A100018 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: b4duqeboqjznmgs84484pt5pqi17iqf3 X-HE-Tag: 1688986722-353490 X-HE-Meta: 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 LM+HwNr5 ZbSJbpfbph2UmayNfyoyzaIkqMcF/Ew370dDNRnJ6uKaZptmWp5twcdt57r3SCQGkp29XU0iyi2wtAjsib3HubBiFhnH15QwTzlc+UGfMsYwAyNkrxNuJXtoorDVyQ0NTxF5kp85V84aTekA8FniGL/5+wvMD9H2w8rjOBTef62lHx2t7ALjrIok4cOSI4f+qiuFU/s2WhYixuCgbd5el/iGG3QV0O1ypZhsJBFK2hiv8lyKjYlpb7EtzBg+/H+UDR+f02d3WwW32VWVfelgv5G98hfYEUI5RDFjxWCeZYhZlCUmei2vW0kMUvC9xLzRhpPbRvL9u7cmjF3Pkl+E/NB6999S2d5+eWDWidrsJvaEI7ut7X8RWr/PCYt7bjy8cgpsKPYcRDmnMftc7JI3BO7fgTwH3B+iuR4saqnNxdJySII4u6Ls3+vv4yeubOyrkkS8jbC4E3bHHd+aEFqMNm8xIqA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 在 2023/7/10 18:37, Alexander Potapenko 写道: > On Mon, Jul 10, 2023 at 5:27 AM 'Peng Zhang' via kasan-dev > wrote: >> >> kfence_metadata is currently a static array. For the purpose of >> allocating scalable __kfence_pool, we first change it to runtime >> allocation of metadata. Since the size of an object of kfence_metadata >> is 1160 bytes, we can save at least 72 pages (with default 256 objects) >> without enabling kfence. >> >> Below is the numbers obtained in qemu (with default 256 objects). >> before: Memory: 8134692K/8388080K available (3668K bss) >> after: Memory: 8136740K/8388080K available (1620K bss) >> More than expected, it saves 2MB memory. > > Do you have an understanding of where these 2MB come from? > According to your calculations (which seem valid) the gain should be > 290K, so either 2MB is irrelevant to your change (then these numbers > should be omitted), or there's some hidden cost that we do not know > about. I don't know why the 2MB memory was saved, but it looks like it has to do with the .bss section, maybe removing this array affected the linker?