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Tue, 7 Jul 2026 10:40:31 +0800 (CST) Received: from kwepemr500001.china.huawei.com (unknown [7.202.194.229]) by mail.maildlp.com (Postfix) with ESMTPS id EC2F64057D; Tue, 7 Jul 2026 10:49:10 +0800 (CST) Received: from [10.174.178.9] (10.174.178.9) by kwepemr500001.china.huawei.com (7.202.194.229) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 7 Jul 2026 10:49:10 +0800 Message-ID: <2b4b3fec-18e4-48da-8ead-82d0c4970c08@huawei.com> Date: Tue, 7 Jul 2026 10:49:09 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fs/proc/task_mmu: count KSM-placed zero pages in smaps To: "David Hildenbrand (Arm)" , , , , , , , , , , CC: , References: <20260706121323.1149847-1-tujinjiang@huawei.com> <6ef49a9f-af0c-4bce-8402-16926424ea7a@kernel.org> From: Jinjiang Tu In-Reply-To: <6ef49a9f-af0c-4bce-8402-16926424ea7a@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.9] X-ClientProxiedBy: kwepems100001.china.huawei.com (7.221.188.238) To kwepemr500001.china.huawei.com (7.202.194.229) X-Rspamd-Queue-Id: DDA6C40002 X-Stat-Signature: a74g88rerk3nmp71dipukxhrxgi8dk1h X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1783392554-221608 X-HE-Meta: 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 Mu6mYzvg aD7163sN3PvP2WG73sk9WEYokm5lLelWfPvnR/BH50XHBwqOCwcj4VM2FQy47G20KUP6d9KirCcN7RxroT41LftdMP39vSPhfG8+4LIHGdt5B7FsTfMR/UwGvvfcWKbMuy9gzIKO2LuhbcQ9U5eymZY3TBFRaC6ej5nKYCiS+Vqxed2KDrxHDfY5pmiWPfVpVj8+aZPb1z03jukSLzdCXnhwkj1qGXkwDPnK9TgR2M1QuOS5dWsup+Mj8QbbB5B9n4729Pyxd90XoeV7JHqvZ0OUYNaW50fc0LtN2R3s92mwDzfKxKLJRpTw7pi1qt4Vz+On2MNd1mom2+L8odk5daDW22SVn6QKfoQYi8fatMBcwaH49/hXPW10Hm3yfNMVqfAaVIjtC61Nz1q0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 在 2026/7/6 21:40, David Hildenbrand (Arm) 写道: > On 7/6/26 14:13, Jinjiang Tu wrote: >> When KSM deduplicates a page to the kernel zero page (i.e. when >> /sys/kernel/mm/ksm/use_zero_pages=1), it places a zero PTE with the dirty >> bit set. vm_normal_page() returns NULL for such PTEs, so smaps_pte_entry() >> bails out before reaching smaps_account() and these pages are never counted >> into mss->ksm. As a result /proc//smaps and smaps_rollup report a KSM >> value of 0 even though the region is fully merged. >> >> Count KSM-placed zero pages directly in smaps_pte_entry() using >> is_ksm_zero_pte(). > Hm. > > We do expose "ksm_zero_pages" in /proc//ksm_stat for calculating the KSM > profit. > > Why would we want to expose it here as KSM pages? > > An application will notice the difference between "zeropage enabled vs. > disabled" either way because we'll also not account zerpages towards e.g., > "Anonymous". > > So faking that something consumes memory when it actually doesn't consume memory > is wrong? Indeed. As Documentation/filesystems/proc.rst says, smaps shows the memory consumption of each mapping and flags associated with it. KSM-placed zero pages shouldn't be accounted.