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Sun, 04 Feb 2024 18:05:49 -0800 (PST) X-Forwarded-Encrypted: i=0; AJvYcCVspSycYoIEXn4EgPZz7USoAoUFNLMU/8YDPVu6q/bF+OElJehghZkpfpgkoSsXTccwcG7aH9mG22TmU81aGJgC1CzbACMVutQROUUnzkgl+HummRTkXxn+DImzjz4YgmIJM6sT2hOuMKBNi9AxnraUSFPW4Gih3sg2+BZcDSHDqEEsrnbGVk/6EwO+So0Z9RpIi8o2ugDeLG/Kqum/1eTpZ+GYE6W1eRXia+S2qz9JZGCUsJ0= Received: from [10.255.134.6] ([139.177.225.228]) by smtp.gmail.com with ESMTPSA id mn16-20020a17090b189000b0029696f7f443sm966122pjb.50.2024.02.04.18.05.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 04 Feb 2024 18:05:49 -0800 (PST) Message-ID: <7fad74d9-134e-4606-abf7-3969ca01acef@bytedance.com> Date: Mon, 5 Feb 2024 10:05:42 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: pgtable: add missing flag and statistics for kernel PTE page Content-Language: en-US To: Matthew Wilcox Cc: akpm@linux-foundation.org, arnd@arndb.de, muchun.song@linux.dev, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org References: From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: ybudbs7se5ypzhhozsiakq36gru6baug X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: EAB6A120002 X-Rspam-User: X-HE-Tag: 1707098750-399732 X-HE-Meta: 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 pa5FrrwM HaiZoNhCSnIuDq2pckQx3Fhwxnb09kBTivNzfj5RM/9tpSI+vy+qPeSFQNDA4QamBo9ZaTXXi31ePTHOsQJsyR0XWJHkZij+V1m3zJ/70twA0lfUi0sRBPa47y+LX8UlhjUX/yMmidR01uF+W5cpprqwfK6cFjw7SVib0xokJ4TA4rdSVlnfU2Wg5AmkTdda28gom7GmfJdEdCRh5fbbk3Qz+gj0zhtDDZbdQxfgtvWYwqvE5L9RbdAB9NmUYQ+jT6c2kCbEBGzE0QYzJ8UcsnrTFf2vGTbyKMr0Sd5bvc0cOkGpXGoUih4k9na0f+QLWlHR72Xi5NN95XcrOL62jyLB8V3nVuJ8Vt16wKzMFBxsJ3HmBobIhxOIZfpCiRksyU7TMudrYEiinkyYDKfFHXla3Lw== 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: List-Subscribe: List-Unsubscribe: Hi Matthew, On 2024/2/5 02:51, Matthew Wilcox wrote: > On Thu, Feb 01, 2024 at 04:05:40PM +0800, Qi Zheng wrote: >> For kernel PTE page, we do not need to allocate and initialize its split >> ptlock, but as a page table page, it's still necessary to add PG_table >> flag and NR_PAGETABLE statistics for it. > > No, this is wrong. > > We do not account _kernel_ page tables to the _user_. Just because > the kernel, say, called vmalloc() doesn't mean we should charge the > task for it. Moreover, one task may call vmalloc() and a different task > would then call vfree(). > Got it. Thanks for providing this information! > This is a can of worms you don't want to open. Why did you want to do > this? Ah, just because generic {pmd|pud}_alloc_one() has opened it. ;) And When I looked through the commits (e.g. commit 1d40a5ea01d5), I couldn't find the information you provided above. And that is why I CC'd you to double check this, in case I might have overlooked some important background information. So we should actually fix generic {pmd|pud}_alloc_one() (and maybe some implementation in the arch), right? And it would be better to add some comments to clarify. Thanks.