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 C643A4BB28E; Mon, 21 Sep 2026 15:31:56 +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=1790004717; cv=none; b=Q434pHUWcgvbixnQ/Zstb8DeyWnQDJOe8W0QWguuxWFBefwdvN1188SsoIklsZJsQ0UruYGF3wpdD6XlDxEfuYm9O3CtpADxypGuMPcm5X45KA1BRDO0e9Co+5yBNwqvTVYNOTNK53SK5Ju5Cb4+WKuakHkdDDLpMC8PZCspNu4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790004717; c=relaxed/simple; bh=Zhun9bmg0CRQi5K4hjUQKXMbPDPpc1D1fATRLPF5MqQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qEY/QoV3dgJQqEnMAx0t+nMJD+T/OvXaCqlgeWtQ/ws110t4Qq4jAi72UwmnSglonPzo7s+lCQehMbdrCrBDcF7TUNQqZLZhexQ7hI0gEvtpYq7neOMYM5aglFiz5E+4+ekOIKUecnj5kLBVxBr01+laMdUkex2QNG2IN9VKfzg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BpWnWfx2; 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="BpWnWfx2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A0C741F00898; Mon, 21 Sep 2026 15:31:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790004716; bh=FuUrqWc9bTGN2ILuKnc9hMdv0vV4JMwCLib1Eff7GPo=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=BpWnWfx2ds3Fe0emxSeG9TZPaU0fjs6BNTQP9KkoI+3KJtqZ/c53fPAcFTUWz4E1b 23fgyM9QIldp/Ud7j2JcDXbZR7MY3ffMBZMYTMjb7RHPDAQdV9oFWu/rPLi9x75GdW wqLix0oxA7ZjiuZuAA5szff+krYbGlVAY60Gh+q5/5mdR9xpLfCA1oHMoqB6akI1o5 xPtXZ8W9vQG4uA61wqDz1XOlOPTV8POlHsKzV5yG8b+GNPUIXpVntti06qvivtGb+H 4qVvcrlSiYCVXujkEwaEmTL5GzWaUz1EzJqeRGnEicy8fFZx6Er5LvVSJrxOpJSCqA krGUh0imuKFzA== Date: Mon, 21 Sep 2026 16:31:53 +0100 From: Harry Yoo To: "Vlastimil Babka (SUSE)" Cc: Tim Menninger , linux-mm@kvack.org, Chuck Lever , linux-nfs@vger.kernel.org, Jon Curley , Eric Badger , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [SLUB] nfs_page cmpxchg_double_fail and perf lock perturbation on dual-socket NFS/RDMA Message-ID: References: <20260917162533.600472-1-tmenninger@everpuredata.com> <8705aa4f-5e02-45e7-ad45-0baa982a8c02@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8705aa4f-5e02-45e7-ad45-0baa982a8c02@kernel.org> On Fri, Sep 18, 2026 at 09:08:37AM +0200, Vlastimil Babka (SUSE) wrote: > On 9/17/26 18:25, Tim Menninger wrote: > > It reproduces with slab_nomerge. > > > > I booted the same kernel with: > > > > $ cat /proc/cmdline > > ... slab_nomerge ... > > > > Uninstrumented throughput remains in the high-45 to low-46 GB/s > > range, as before. During perf lock it was around 30 GB/s in these > > runs, versus roughly 25 GB/s previously. > > > > The dominant lock measurements are essentially unchanged: > > > > default slab_nomerge > > unpinned/node0 > > contentions 4,782,839 4,858,759 > > total wait 14.39 min 14.26 min > > average wait 180.47 us 176.13 us > > > > node0/node0 > > contentions 4,582,012 4,686,729 > > total wait 14.13 min 14.34 min > > average wait 185.05 us 183.53 us > > > > unpinned/balanced > > contentions 4,572,196 4,544,677 > > total wait 12.81 min 12.56 min > > average wait 168.14 us 165.84 us > > > > The uninstrumented cmpxchg_double_fail deltas were: > > > > default slab_nomerge > > unpinned/node0 7,471 8,892 > > node0/node0 713 457 > > unpinned/balanced 1,503 1,504 > > > > The CPU-utilization change while perf lock is active also remains. > > System-wide %idle for uninstrumented/instrumented windows was: > > > > default slab_nomerge > > uninstr. instr. uninstr. instr. > > unpinned/node0 31.46% 3.60% 23.02% 2.15% > > node0/node0 84.26% 12.07% 84.62% 11.85% > > unpinned/balanced 66.86% 14.83% 66.58% 14.78% > > I believe the weirdest part in the original report was how slub stat > counters such as free_fastpath etc got order of magnitude higher with > instrumented vs non-instrumented. > Did any of that change with slab_nomerge? If it didn't change, that'd be very surprising. ... unless perf lock was writing data to an NFS filesystem? -- Cheers, Harry / Hyeonggon