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 4D5C4DF76; Thu, 16 Jul 2026 11:20:48 +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=1784200849; cv=none; b=N9nGxquIhKQfHQmAiWaxXWAn1Qb0tn4lxj/1KPLK2Z1OdDJD8ra1ZdItV5Mz9UmGgjPCXtEtIpyK04pUE8VkwOhPr2+p0351uAXlReSRpxOR0aK+THHrS9Jz2yWAByDc1vsoaaeNZI5+6+BCA4zygOLjTpTja/RYKdBO5DoXpGI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784200849; c=relaxed/simple; bh=QK7N3/wsTvX1kN/spYWC/FGRFpFg0+xkagkwjKwI3yo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aM+/1IoMEA6Y2909aD2eGNTqwn3IMnJo9OATtcQjyjNcoX1hQfZEzP5cmUeC29avMw+ttIYCCWy3lE/QXKhzxJO0U0Cz+vBCpBmZdjv35zbNgaVn5TtLiA/Np7rz3olAEaScXJR946/6wNcBnvcSkFm57/65VHIP9OylPGGSltI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ULJ8jTJL; 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="ULJ8jTJL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E22731F00A3A; Thu, 16 Jul 2026 11:20:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784200848; bh=iohMITS/mr9qDiRkI+rGRUr759u+rXGlGlDEwpj+fhU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ULJ8jTJL674cLd5oJIqYzCX17btEY5HF91TfblR8ew2LU3w2GS1H8qpYVf+Ss+vYa A4kPjTsJPQcIq0ZhsQvwyxrUv1aoJE2X/5vZv4WNyPyDYs7quFjED/Aaw8NFKpB2TT 7MWIIwG0eLp2UyYHic9Ix8F3s2XnZlUGX1584c/xpCOlkdUEeooD4LRHnoOQU6DLxR 9pp7/6d6UvA8aaNkL8MqGEA9g+Tncqanp9i97hDdqwCABUrTWW/23hhjFLIW5uUbxT lAFu++ONA29JTBj6BAUInoCpeJa5B+uqqSiGLXUbRmmvbU62WXI6+bIAyzWPP59ka8 J/5pwZXkY5Ofg== Message-ID: <0c278b69-3ecd-4ec3-b418-dea84e043732@kernel.org> Date: Thu, 16 Jul 2026 13:20:45 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] selftests/mm: khugepaged: skip swap tests when swap is unavailable To: Dev Jain , Jaeyeon Lee , Andrew Morton , Shuah Khan Cc: linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260715133418.170386-1-jaeyeon.lee.dev@gmail.com> <4b6904b5-81f9-4e27-8ac5-5bd7e7174c5d@kernel.org> <6c474ce7-8f1d-4e85-8587-8a60983cec03@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/15/26 16:47, Dev Jain wrote: > > > On 15/07/26 7:39 pm, David Hildenbrand (Arm) wrote: >> On 7/15/26 15:34, Jaeyeon Lee wrote: >>> The collapse_swapin_single_pte and collapse_max_ptes_swap tests use >>> MADV_PAGEOUT to swap out pages before verifying khugepaged collapse >>> behavior. On systems without swap configured, MADV_PAGEOUT succeeds >>> but the pages are not actually swapped out, so check_swap() returns >>> false and the tests report a failure. >>> >>> These tests cannot run meaningfully without swap, so a missing swap >>> area is an environment limitation rather than a test failure. Detect >>> the absence of swap via /proc/swaps and skip the affected tests >>> instead of failing them. >>> >>> Signed-off-by: Jaeyeon Lee >>> --- >>> tools/testing/selftests/mm/khugepaged.c | 25 +++++++++++++++++++++++++ >>> 1 file changed, 25 insertions(+) >>> >>> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c >>> index 10e8dedcb087..f9b4ebe733ce 100644 >>> --- a/tools/testing/selftests/mm/khugepaged.c >>> +++ b/tools/testing/selftests/mm/khugepaged.c >>> @@ -100,6 +100,22 @@ static void skip(const char *msg) >>> exit_status = KSFT_SKIP; >>> } >>> >>> +static bool swap_available(void) >>> +{ >>> + char buf[256]; >>> + bool ret; >>> + FILE *fp = fopen("/proc/swaps", "r"); >>> + >>> + if (!fp) >>> + return false; >>> + >>> + fgets(buf, sizeof(buf), fp); >>> + ret = !!fgets(buf, sizeof(buf), fp); >>> + >>> + fclose(fp); >>> + return ret; >>> +} >>> + >> >> That doesn't mean that swapout will succeed. >> >> Take a look at cow.c where we use pagemap_is_swapped() after MADV_PAGEOUT. > > That suffers from the reverse problem - in case of a real swap bug, cow.c > will skip the test and anyone running the test won't bother. Yes, because there could be other reasons why MADV_PAGEOUT would not be successful (speculative page references, out of swap space). > > I think this patch idea is reasonable, we need a way to say "swap definitely > won't succeed because there is no swap device, so skip" vs "swap failed, > need to dig in!" . I would not pack a "let's test if swapping in the system even works" into a khugeapged test. I think we can reasonably assume here "swap subsystem is not completely broken". And if we want to check for that, have a separate test that stresses swapping, if available. -- Cheers, David