From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 213F648424A; Mon, 31 Aug 2026 14:03:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788184984; cv=none; b=FCHhqD+U2cyxffX1b94eHoCW2/yiPRaXXQydyjBUSbyhc2kowBcpp2aiKpnVG+pzKHJXNoVPqVh3a3eeSYQ3wjmoBhV6bxbhwm1aC+d5zYHg/STCOqciuXzLEoF9TzfnSBmqJG8SkMtGy2JeNmeBvP+w/XmNdCKJs+s+lP2/MvY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788184984; c=relaxed/simple; bh=c8YnLYM9gCkCamNMX4Ifu9ihjCO2crXUFIBol3Mz1aU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mgTZRnUGfaKuSxI7fqh94XJEi1GZ0aiKRPDaw+xnc83Cj6GqcvuDxzT4jg111Cw0rNBl79njakJN+gj6tW/s5yS/kQbz5fULibghHUQJrzj9jRfNCID8mddrui5p35ewNFR1QmmcyPsLjcEV0UEe2Pp4lZXAD/pCMWFF2O455hQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=h+1eIXDe; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="h+1eIXDe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BC6771F00A3F; Mon, 31 Aug 2026 14:03:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788184983; bh=ccJR9KUzvn7k6BzhoDEjN3sQrL1C2MxY/yOiNOzvC90=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=h+1eIXDeQBAQUEQT+BHPoIt3p/SRP8E+YgRQDpNx0ek9JHPXbuwO0QBybw+PfjfrZ hHRD5xsWcY4EoIhMgDT5cKTMNKxOib1aMBeU16mcgv74zbIVZWmtnqNJN7V06osC1H fGo60DV1jRBKLrPXpVjoq7fpmZQixJNKqZrtZiyfvmDTetdnUjdoTkurf8aSfVAOC8 6R5+j/oVhpV9iY6JWJzQf9zH4CJCLSG+WS3q2Qyshrnr6PK/kv41ElGi8FUn6W/3lq 0CHnlRxIWF45bMsV6ZfHPw9oroitEgD6q9hNcqHfNa5f4YCvca5kLlfldmIZyoXVe6 oBDRf+zfa/ZXg== From: SJ Park To: Cc: SJ Park , stable@vger.kernel.org, Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v1.2 1/8] mm/damon/core: skip applying scheme if region split for quota fails Date: Mon, 31 Aug 2026 07:02:40 -0700 Message-ID: <20260831140254.72004-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260831140254.72004-1-sj@kernel.org> References: <20260831140254.72004-1-sj@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit damos_apply_scheme() splits a region and apply the action to the subregion if it is needed for not violating the quota. The split operation (damon_split_region_at()) could fail for allocation failure. In the case, the quota could be violated. From the user's perspective, DAMOS becomes more aggressive than expected under the extreme situation. Handle the failure. The user impact is not critical. The failure of damon_split_region_at() is unlikely since it is arguably too small to fail. Also DAMOS being aggressive is limited to the single region. Users can set min_nr_regions to set the maximum size of each region. If it is reasonably set, the transient overhead shouldn't be critical. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260718171523.87547-1-sj@kernel.org Fixes: 2b8a248d5873 ("mm/damon/schemes: implement size quota for schemes application speed control") Cc: # 5.16.x Signed-off-by: SJ Park --- mm/damon/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 644daf5a16560..e2900d0c984c9 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2613,7 +2613,8 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t, c->min_region_sz); if (!sz) goto update_stat; - damon_split_region_at(t, r, sz); + if (damon_split_region_at(t, r, sz)) + goto update_stat; } if (damos_core_filter_out(c, t, r, s)) return; -- 2.47.3