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Sat, 21 Mar 2026 23:06:34 -0700 (PDT) From: Liew Rui Yan To: sj@kernel.org Cc: aethernet65535@gmail.com, damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [RFC v2] mm/damon: add synchronous validation for commit_inputs Date: Sun, 22 Mar 2026 14:06:30 +0800 Message-ID: <20260322060630.82964-1-aethernet65535@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260321173235.84923-1-sj@kernel.org> References: <20260321173235.84923-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: x8bqhnjjanchwmyh4x15spfkdwncnt6u X-Rspamd-Queue-Id: 9954B2000E X-Rspamd-Server: rspam03 X-HE-Tag: 1774159595-376572 X-HE-Meta: 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 SlWKCjpb AtGnjsDXZLwp1CEBIYT69tGz2o39BnNktQrBsdUYTx7zoKTwiikviT/7ecF+Xnpj1LHCatL1EpM+4FzFa0Uz0iPuk3f48y36GkfPI7fajfT3Tw+8pY8xHF3J7EwWrTdXKj5YqyiBF5l3D5tMuYy5Iqzm8n+1LC9+ApDnZlJ8bw69DWsVBsYUUM7OW+/9m12CSYysA1LW8L4Dxyz0CGnpRfnPijziPxz1WAOz80KnBtZMnadzdRKxwLpCwIro9Ex0yxvhYXeR7m7/IV5i+ZI4pc2Ly8GbUnWWr0ktOjoichhWZz4u/I/9z4RKoNkRFFHpERPSOXyLTptFYm41h3oaJCKOomp/ORDS4TRW8yf6Ms4IUsQsMi+TGVKvdhOWxrM81C9qa7zyoUrb479juAaEqxwGe7z3r7qbRg8tq4aYS9tpN39rxFtzNKficF0kavDmSlL8yrGEk2XUuCMo8XdA3BCb1Z78jRnik7Ouq Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi SeongJae, I tried implementing the synchronous commit using damon_call() as suggested, similar to how damon_sysfs_commit_input() works. This successfully returns errors to userspace immediately instead of failing silently. However, I observed a side effect during testing: Since damon_call() waits for the kdamond thread to process the request, the latency of writing to 'commit_inputs' depends on the kdamond's wake-up interval (controlled by damos_watermarks.interval). In my test with DAMON_LRU_SORT: - With '.interval=5s', the write latency can be up to ~5 seconds. - When I temporarily increase '.interval=50s' for testing, the latency increased proportionally. I understand this is expected behavior for synchronous communication with a sleeping kernel thread. However, since 'commit_inputs' is a control interface rather than a hot path, I wanted to comfirm: Is this level of latency acceptable for the 'commit_inputs' parameter? Or should we consider waking up the kdamond thread immediately upon receiving a damon_call() request to reduce the worst-case latency? For reference, DAMON_SYSFS seems to have similar latency charactheristics when using damon_call(). Thank you for you high-level comments and the suggestion! :> Best regards, Rui Yan