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 D6E08286D7D; Sat, 11 Apr 2026 23:34:38 +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=1775950478; cv=none; b=YP0XLZ4Zh/6fI8a3czRgY6loaPGrGrRt4KesCEBGNr281EF1yfZE0vUfcqnqaxBIG9UWAgB/wMNlbs6CnHbSFqwuWEfR7NhhmSsg5tsEQjxh0mnMgs92h8wrGe9uTOpXByxhAwtPvK15/r9m/ecFNgFBvWyG64Uradi960oAw3Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775950478; c=relaxed/simple; bh=6hgRkVSjVQ54vQbr1xRhJZ/6jdyx+6uY8s9yPTjVW2w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VN6T5oZCF94uNDj6nrBc/acBBa4WdGu0Q3rGAnFpOkfc2g6g6pWvDRyeo/hriSkbFZX+GTmk4SnPGoZYDjAH5f8nFk55598Cyt9WeUSrQTU4QRMiaQMumzxm30Gp6tgNkqBYoNEG4QfgnQsKBv1/3McR/eANZangXvq6LmlqNkM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=J6X95oTb; 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="J6X95oTb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5133AC116C6; Sat, 11 Apr 2026 23:34:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775950478; bh=6hgRkVSjVQ54vQbr1xRhJZ/6jdyx+6uY8s9yPTjVW2w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=J6X95oTbOAS3XyTF0Dmt6wrD17Kvgl97r+sYxRrN3bzDEaNkg+d2uLZfGFngtgb9a rahioNH2tDN2hSjLgrp49QPC5chnLUOXdclMlOl3EjWCR6AJ4JG0XcB9mtn2e63AaN 9G47GhDisB6kb4+bOH4cqao/EDJW6bTWRbh6H8QZ9S8Nc7AhbFEnaQGr3V8e5fn+2E PrLcdPKyHMukj0XKaa2J57USMBGYr/JI4xH9Rrja6wYCd89g0p/ZiJfo/rOnyacf4U HpW0xB1QdECfsjlYxYkgro8hIeY7IBCaw18ZNWPUzB28ARfFk8X6wf8Bf33aTzR7/m 2LxJ5v/6Im24g== From: SeongJae Park To: SeongJae Park Cc: Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [PATCH] mm/damon/core: disallow non-power of two min_region_sz on damon_start() Date: Sat, 11 Apr 2026 16:34:30 -0700 Message-ID: <20260411233431.78220-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260411213638.77768-1-sj@kernel.org> References: Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit TL; DR: sashiko found no blocker of this patch. Forwarding full sashiko review in a reply format with my inline comments below, for sharing details of my view and doing followup discussions via mails if needed. > # review url: https://sashiko.dev/#/patchset/20260411213638.77768-1-sj@kernel.org > # start of sashiko.dev inline review > commit a125056db470cab021e84ad481a0f51ddfc426c2 > Author: SeongJae Park > > mm/damon/core: disallow non-power of two min_region_sz on damon_start() > > This commit fixes an issue that allows unaligned DAMON region address ranges. > It adds a check for power-of-two min_region_sz directly in damon_start() > to catch invalid configurations from the sysfs interface. > > Link: https://lore.kernel.org/20260403155530.64647-1-sj@kernel.org > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > index 3703f62a876b3..c107d74c77e74 100644 > > --- a/mm/damon/core.c > > +++ b/mm/damon/core.c > > @@ -1368,6 +1368,11 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive) > > int i; > > int err = 0; > > > > + for (i = 0; i < nr_ctxs; i++) { > > + if (!is_power_of_2(ctxs[i]->min_region_sz)) > > + return -EINVAL; > > + } > > + > > This isn't a regression introduced by this commit, but modifying > damon_start() brings up a question about partial failure handling when > starting multiple contexts. > > If __damon_start() succeeds for the first context but fails for a subsequent > one (for example if kthread_run() fails), the initialization loop breaks and > returns an error: > > for (i = 0; i < nr_ctxs; i++) { > err = __damon_start(ctxs[i]); > if (err) > break; > nr_running_ctxs++; > } > > Does this leave the previously successful kdamond threads running without > stopping them? > > Because nr_running_ctxs is incremented for the successful starts and > running_exclusive_ctxs is set to true, it appears the internal state > would prevent starting new contexts. > > Would this result in all future calls to damon_start() returning -EBUSY? Yes, this is not ideal. But as Sashiko also says it is no blocker of this patch. I will revisit this later. > > > # end of sashiko.dev inline review > # review url: https://sashiko.dev/#/patchset/20260411213638.77768-1-sj@kernel.org Thanks, SJ # hkml [1] generated a draft of this mail. You can regenerate # this using below command: # # hkml patch sashiko_dev --for_forwarding \ # 20260411213638.77768-1-sj@kernel.org # # [1] https://github.com/sjp38/hackermail