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b=mZVhN5KlL11K88wefykFNw4z0BUVVaYN+y7IX2XX1QMgigoA+xMSnAjA61UnQT+rd vemx26JRp2EEMsXbJDnOVg4t0JlQxKF86RJ84qZJuRigcnmixLwXajrPFQp2ARiekJ kBL2aAHsuryGKnwU1ozP++iK8aK4els6QMxWiq6YkcECh2oLlH93urvXwe/yH15IIb tBTnl8yZlXbNQeV0cxiI4IUS8/jcPqwj0WNdaZ1KMkT/9kCZuV1NwbZWHdfM0QRb6f wnyFkUWB3uaDe4OJqv202bnVbc2P+fVGfPNtI6Q5ro4FO+XjydWdbxCip3rGi7wwsp y6O85Rk62cy0A== From: SeongJae Park To: Liew Rui Yan Cc: SeongJae Park , damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [RFC PATCH] mm/damon: reset thread status parameters upon kdamond termination Date: Thu, 2 Apr 2026 06:54:39 -0700 Message-ID: <20260402135440.74339-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260402053458.26524-1-aethernet65535@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 3FEC51C000A X-Stat-Signature: x6r99xb5aw3frzmd6r17demh3b79nnac X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1775138083-423394 X-HE-Meta: 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 ws//0qFf 8V9EO3MHGZK2wUtPeU/7Te8wec3pkMier+CofhqMaMKlvThIQoWKu+NH9p2LQ4lL22vpKeUf46uAnjQ2lFhyZPe045OjuvlaMA1MFkddkb0Ck2M84Qt4X/S6cDh3eBH36Enk8MZcPMNKJSmEm70M4iSLMpods2xRkp/Xq8jPPzPEnsnJSKYv7MU8fDTk1lgXxnso0Bsvz2V8OmBLiw0MjSDgbnmEZZVvpycij0WgZ3N7GSJzmY+cU5lJZct6YIWArP7Kz Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 2 Apr 2026 13:34:58 +0800 Liew Rui Yan wrote: > Hi SeongJae, > > On Wed, 1 Apr 2026 08:41:18 -0700 SeongJae Park wrote: > > > [...] > > What about checking if damon_call() and damon_commit_ctx() failures via therir > > return value? It seems damon_call() fails only when kdamond goes to the > > termination path. damon_commit_ctx() failure always causes the kdamond be > > terminated. So if I didn't miss something that could be a path forward. What > > do you think? > > Thank you for the suggestion. I looked into the code and I think > focusing on damon_commit_ctx() failures makes sense. > > Specifically, damon_call() is only used in the damon_{lru_sort, reclaim} > _enabled_store() path, which doesn't trigger unexpected termination. The > main risk comes from 'commit_inputs', which calls damon_{lru_sort, > reclaim}_apply_parameters() . When damon_commit_ctx() fails there, it > reliably indicates that kdamond is terminating. > > My plan is to add the error check directly in apply_parameters(), right > after damon_commit_ctx(): > > err = damon_commit_ctx(ctx, param_ctx); > if (err) { > enabled = false; > kdamond_pid = -1; > } > > This covers the reproducible case (addr_unit=3 + commit_inputs=Y). > > For truly unexpected termination (e.g., memory allocation failure inside > kdamond), I'm considering a fallback mechanism in enabled_store(): > > - When the user writes 'N' to 'enabled', if damon_stop() fails but > kdamond is actually terminated, we reset enabled and kdamond_pid. Sounds good. > > - When the user writes 'Y' to 'enabled', if enabled is already 'Y' but > kdamond is terminated, we treat this as a restart request. This sounds bit odd to me. User shows enabled=Y and kdamond_pid!=-1. Why they would write 'Y' again? Yes, they would notice kdamond is terminated in real, using 'ps' like tool. But even in the case, I'd imagine users would write N to enabled first, and then write Y to enabled. In other words, this could improve the user experience, but seems not really necessary to me, at least as a hotfix. What do you think? > > This way, even if kdamond terminates unexpectedly, the next user > interaction will recover the state automatically. > > Does this approach sound reasonable? Yes, the plan for the next version sounds good to me. Thanks, SJ [...]