From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A90F03D561 for ; Tue, 14 Apr 2026 00:23:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776126183; cv=none; b=IAtIeE6V5XV2ktFvEuxaPWlDyOiVvCHJvnPtQiWaF0zuu/PM87xzZbXM+neIvx1lEDBo0CQkYscNwMqmpb+hqXNvO8gbTYZDGo70kLDVyT1EXLiX5VHgx4LiXu+sZ3gKGuedbp+6uaWfApYSqSWNLwYYJY+AZ43k9V6BQWHNJts= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776126183; c=relaxed/simple; bh=rUPIO44OS0Rco3GvN57c0BXurHCc9flcjQqmcQyfIfs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OuUV+0LO986+BSVCVpTUszMn5IuzDbaKYqLmNzCiR+EJMCkW15IOm8tf7vE4WglU6RdgGrzJnjMo0Sckrw48Izj/1lg7y3PwcOqtDeSVAb9PbJP6zTy1xOqMPlokDIUcSVG+iSO9CgOLdkdKrDPQrDqMV5Girt00ymWMyBpFN4U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UFC+xDNx; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UFC+xDNx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 678E7C2BCAF; Tue, 14 Apr 2026 00:23:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776126183; bh=rUPIO44OS0Rco3GvN57c0BXurHCc9flcjQqmcQyfIfs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UFC+xDNxVZ7H1zSIPMZdUup9eX9wkebQIij2neJzsBGlAmCV1TP3+NbVMlx0yhypt ka+4TLqgz0AIa7O/2RJP0uzCvgdrht1PDh/cMt013nUTCqmxIeRcunnUF8NavZrM9D VDPAJJqDa8wl6UkgNfoXDEK4dM/z8jj3XmyMsEb9b0IJpJpsGBq15dFrpmcBVesv3E 6OARsnGZz8qFFJvHcjGBeaE0n299WE53HUNIcL0k9mQyclsjsIwsweW3iITzy/VuMO l5b8fgU0A578t3osFs9cObvaGrGfPPCfgOQeujnNdTEUf6H6izFidliLGlg+fF0i5t cxYxHK78vUzMw== From: SeongJae Park To: Liew Rui Yan Cc: SeongJae Park , damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [PATCH v2 0/2] mm/damon: reset thread status parameters upon kdamond termination Date: Mon, 13 Apr 2026 17:22:59 -0700 Message-ID: <20260414002300.83328-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260413185249.5921-1-aethernet65535@gmail.com> References: Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Tue, 14 Apr 2026 02:52:47 +0800 Liew Rui Yan wrote: > Problem > ======== Let's align the underline with the subject. Also, let's add one blank line after the underline. > When kdamond terminates unexpectedly, 'enabled' remains 'Y' and > 'kdamond_pid' remains stale. This prevents user from restarting DAMON > because both writing 'Y' and 'N' to 'enabled' will fail. > > "Unexpected termination" here means the kdamond exits without any user > request (e.g., not by writing 'N' to 'enabled'). Could you please further explain when such termination can happen? > > User Impact > =========== > Once kdamond terminates this way, it cannot be restarted via sysfs > because: > > 1. DAMON_LRU_SORT/DAMON_RECLAIM is built into the kernel, so it cannot > be unloaded and reloaded at runtime. I think this is quite obvious, so may better to be dropped. > 2. Writing 'N' to 'enabled' fails because kdamond no longer exists; > Writing 'Y' does nothing, as 'enabled' is already Y. > > As a result, the only way to restore DAMON functionality is a full > system reboot. Thank you for clarifying the user impact. I think this deserves Cc-ing stable@. I think 'Problem' and 'User Impact' can be unified into one section. > > Solution > ======== > damon_commit_ctx() sets 'maybe_corrupted=true' at the beginning and only > sets it to false upon successful completion. When 'maybe_corrupted' > remains true, kdamond will terminate eventually. This seems better to be explained earlier, on the problem section. > > Therefore: > 1. In damon_{lru_sort, reclaim}_turn(): Add fallback logic to reset > parameters when damon_stop() fails but kdamond is not running. > 2. In damon_{lru_sort, reclaim}_apply_parameters(): Reset parameters > when damon_commit_ctx() fails, as kdamond will terminate due to > maybe_corrupted mechanism. So the problem is that 'enable' parameter value is not trustworthy, and this series is trying to make it trustworthy. I think it is bit complicated, especially for stable@ fix. What about simply using more trustworthy information, e.g., ''' --- a/mm/damon/reclaim.c +++ b/mm/damon/reclaim.c @@ -390,7 +390,7 @@ MODULE_PARM_DESC(addr_unit, static int damon_reclaim_enabled_store(const char *val, const struct kernel_param *kp) { - bool is_enabled = enabled; + bool is_enabled = false; bool enable; int err; @@ -398,6 +398,9 @@ static int damon_reclaim_enabled_store(const char *val, if (err) return err; + if (ctx) + is_enabled = damon_is_running(ctx); + if (is_enabled == enable) return 0; ''' > > Changes from RFC-v1 > (https://lore.kernel.org/20260330164347.12772-1-aethernet65535@gmail.com) > - Remove RFC tag. When dropping RFC tag, let's start from v1 again, from the next time. Thanks, SJ [...]