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 33FCB37F752; Tue, 17 Mar 2026 05:43:49 +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=1773726230; cv=none; b=jfWtf9l/3KezTqrr1Mr1S3sUpqRXPf5H3mKGyoS1EQNwiyo7p2lvxBuZqyPlsPfwfN71zeC5mSOUgb99YXsFJwQqmQ9KIK4nerdv2XlnxopE+a+/JL55IUp4+IJse7Fe6IF7HgcXpK2fDi3tFCRCj4SiF+rYIXoFqAuIS+ntw1A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773726230; c=relaxed/simple; bh=aPJSwxGH6jNMzmpJsV3VWFn7DBqjxw2t4PJgg3D/cuw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XDf1fZVbvU8URTV3cQ0JdU/Sg8L7nhQNbVkYHkGmF5m8U3qM+n+8o4/V7JWmNBXYSof5XgxvVYgK4Ytt86eibrx0Onak4UeneWMy0T581F7xiGrIqVoTvmJ8rmls4s+BXLp67bMBSbnw5U8EWMWKUoaa5pAFGVRMJIefZuMiNXQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=P9P16qWF; 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="P9P16qWF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D4F8FC4CEF7; Tue, 17 Mar 2026 05:43:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773726229; bh=aPJSwxGH6jNMzmpJsV3VWFn7DBqjxw2t4PJgg3D/cuw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=P9P16qWF5ooL+iMl2PrfJJDFMJjHxAx856NDb9rJnaSJVoH6HeaE40ymfvWrF6dgt IDNO+1BU/L7bQpZB16aPEttGPgQNyCUp4LydF7OAOEmA8DXIvpY022XOrostvXPJfK hS246hpL/l+jgIOTok0YltjBZL0PggpEib3zodIQS4mXI3d7VwITGLJB6970J7qtlL N4w+eNtWvGvkmRREB4Oz6K+ZFFzwMXrGqlVOMpbNztTrIcWnOAdTbgdagsBC8kpYme QpQy5kurZ3x6/Kv5ncJlLstfAe7Q8y84BIOTxQDrHT3f5LGy5HVG7sBijUrA8DfB1w 1R5hkhGudmOxA== Date: Tue, 17 Mar 2026 07:43:41 +0200 From: Mike Rapoport To: "Lorenzo Stoakes (Oracle)" Cc: Breno Leitao , "David Hildenbrand (Arm)" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH] selftests/mm: add THP sysfs interface test Message-ID: References: <20260309-thp_selftest_v2-v1-1-a00cef41da44@debian.org> <9cb63c24-eaff-4954-97d5-2a422a0401fc@lucifer.local> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Mar 16, 2026 at 07:53:46PM +0000, Lorenzo Stoakes (Oracle) wrote: > On Mon, Mar 16, 2026 at 09:02:33AM -0700, Breno Leitao wrote: > > On Mon, Mar 16, 2026 at 03:44:14PM +0100, David Hildenbrand (Arm) wrote: > > > On 3/16/26 14:47, Breno Leitao wrote: > > > > On Mon, Mar 16, 2026 at 12:55:13PM +0000, Lorenzo Stoakes (Oracle) wrote: > > > >> On Mon, Mar 09, 2026 at 05:00:34AM -0700, Breno Leitao wrote: > > > >>> Add a shell-based selftest that exercises the full set of THP sysfs > > > >>> knobs: enabled (global and per-size anon), defrag, use_zero_page, > > > >>> hpage_pmd_size, shmem_enabled (global and per-size), shrink_underused, > > > >>> khugepaged/ tunables, and per-size stats files. > > > >>> > > > >>> Each writable knob is tested for valid writes, invalid-input rejection, > > > >>> idempotent writes, and mode transitions where applicable. All original > > > >>> values are saved before testing and restored afterwards. > > > >>> > > > >>> The test uses the kselftest KTAP framework (ktap_helpers.sh) for > > > >>> structured TAP 13 output, making results parseable by the kselftest > > > >>> harness. The test plan is printed at the end since the number of test > > > >>> points is dynamic (depends on available hugepage sizes and sysfs files). > > > >>> > > > >>> This is particularly useful for validating the refactoring of > > > >>> enabled_store() and anon_enabled_store() to use sysfs_match_string() > > > >>> and the new change_enabled()/change_anon_orders() helpers. > > > >>> > > > >>> Signed-off-by: Breno Leitao > > > >> > > > >> The test is broken locally for me, returning error code 127. > > > >> > > > >> I do appreciate the effort here, so I'm sorry to push back negatively, but I > > > >> feel a bash script here is pretty janky, and frankly if any of these interfaces > > > >> were as broken as this it'd be a major failure that would surely get picked up > > > >> far sooner elsewhere. > > > >> > > > >> So while I think this might be useful as a local test for your sysfs interface > > > >> changes, I don't think this is really suited to the mm selftests. > > > > > > > > That is totally fine. This test is what I have been using to test the > > > > changes, and I decide to share it in case someone find it useful. > > > > > > > > Let's drop it. > > > > > > Out of interest, to we know why the test is failing for Lorenzo? > > > > I really don't know, but, it sounds like ktap was not found? > > Yeah CONFIG_KUNIT is not set so could be :) Nah, CONFIG_KUNIT has nothing to do with ktap_helpers.sh, probably your environment does not bring in tools/testing/selftests/kselftest > > > > Then the first early-exit path hit: > > ktap_skip_all "..." # undefined → returns 127 exit "$KSFT_SKIP" > > # expands to: exit "" → exits with last $? = 127 > > > > > I agree that the test is a bit excessive, in particular when it comes to > > > invalid/idempotent values etc. I could see some value for testing > > > whether setting the modes keeps working, but also then I wonder if that > > > is really something we'll be changing frequently (and that breaks easily). > > > > yea, I make it very excessive, because there were some intrinsics in > > those sysfs that I was gettingit wrong when doing the intial conversion. > > > > So, the test is something that I trust now, and I found it useful when > > finding regressiosn. > > > > Is is something that will chagne frequently? probably not! > > > > That said, would you like to have a simplified/different version of this > > test? > > In an ideal world we'd use kunit or something to assert it internal to the > kernel I guess, but if we do have something scaled down it'd at least be nice to > have in C? :) > > I am not sure how useful it'd be though overall, I don't see us changing this > too often and really we're more interested in asserting behaviour. > > Sadly THP is inherently tricky to test generally because of its very nature, I > wish we could have better test isolation etc. > > See tools/testing/vma for a forlorn dream of kernel code being run in userland > (but oh how the stubs/duplicate declarations/etc. are a pain). > > I suspect THP could never be given the same treatment though! :) > > Cheers, Lorenzo -- Sincerely yours, Mike.