From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 31010F531CE for ; Tue, 14 Apr 2026 00:34:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5EC116B0088; Mon, 13 Apr 2026 20:34:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 59C1C6B008A; Mon, 13 Apr 2026 20:34:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4B14F6B0092; Mon, 13 Apr 2026 20:34:45 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 383466B0088 for ; Mon, 13 Apr 2026 20:34:45 -0400 (EDT) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id C768B8B549 for ; Tue, 14 Apr 2026 00:34:44 +0000 (UTC) X-FDA: 84655290888.06.EBE4E58 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf24.hostedemail.com (Postfix) with ESMTP id 3C065180003 for ; Tue, 14 Apr 2026 00:34:43 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Jg51ZdQx; spf=pass (imf24.hostedemail.com: domain of sj@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=sj@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1776126883; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=sLHJnCdWa0Cw0/5pmrSPBU0Rz5KofOhsmRu+dPHHofQ=; b=Htfd8bmIM85HDPSRi911UFsX1zw5pq0oSLb/Q0OtspvdVhCHACYmm4mtmYKcORUS+wP8W5 gx4pxPyVEY8Qy3C4NKsSQJkIewACEPq3TUgZDZQKaZr/cE0z/HIHFh7SrTbKB2DwWFdN0u hUqoO5VS0m4GjsFvTDCVJ/Uf8/0WYDg= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Jg51ZdQx; spf=pass (imf24.hostedemail.com: domain of sj@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=sj@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776126883; a=rsa-sha256; cv=none; b=v8SOAMxYyMILOyjGETbgwV5bnx8eWrXsC/cIBFSQwnQq5q+OEy8IqRIhS4tyJCrCu4IIib +X5fRtqlRBSNwKiQzp9dJR9ZEQ/qinWRzK0BqXKUnkbAkcL+F6h9nAQLo/k27A1ag34cpl TBIJsWn9cl7guKkmohxzYMyjaD+ZCQM= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 66A0660018; Tue, 14 Apr 2026 00:34:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EBACEC2BCAF; Tue, 14 Apr 2026 00:34:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776126882; bh=rKC/FuSHBQjUqfWFKqtW02kqh5fExR6jEuIsswCLAQY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Jg51ZdQxMg5FW7/m4sfIFrbXt8FLCSi9kR/RwRMzsKhRmnFDqEdL8L73RM2C9B3wh AJler8tDrsVk0/yJ6fuPr1AnNbEDbMlgCw+mNwSqFc0drWXFj8kXRyUPKOF2VWIpJU /F0gwD5nupZWX5YscBMpB1wUl+5yFVa/eEp2Ch74vLWK2xbUziYv++f2miXuK6BgUD 0FfZx7vkDFPY+XSQ1T91DeieSxicbpAifRVRKRJWbuwGJN5Sz56Ll870Du2roybCu4 UhWJ229SsK4sbL6NhFlcYmRYB/HjlgcdEh5f1tbKr/LetZgP9W/1e1OAxQvZzli3+Y yjms/F07QveFg== From: SeongJae Park To: SeongJae Park Cc: Liew Rui Yan , 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 17:34:34 -0700 Message-ID: <20260414003434.83697-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260414002300.83328-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 3C065180003 X-Stat-Signature: hhkxupwcpwm7nbkqozjikmcjb4foxm66 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1776126883-8458 X-HE-Meta: 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 KyZaVw2C WaHQGUMLpxUVglupeNrMioJ6IbJ+gLu5guRPgtrZkHYrw9Q2dHlQnOwqa4awO5/JliZiR+Y/MqwP94MkKOO47t2+4o/32STDtizOvopMvhAseqrmRowwkL4Lbe7uEa4Hr87UTxpD6JI4xzg73Xmv0FTgmzHX6Y/oBnu7daIF72ANLFKU+QAHaD/a/kIRxCxZRbPSVONo0qp49/x2JTyCYB87/slsaHhfqb4LVww5p+GUJ8/ifk6u4X5JMrT4SWizgdIgo Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 13 Apr 2026 17:23:03 -0700 SeongJae Park wrote: > 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. Also, I just found the patches don't have Fixes: and Cc: stable@. Could you please add those appripriately? Thanks, SJ > > > Thanks, > SJ > > [...] >