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t=1789715324; bh=WCL4dePjhuTX+CGE5tvS1dbBZl4n5dA5dLQyhLK3zT8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Awku+uV8pxJg2xgDDCtl5/l75ccjfY+SVllzMvrfHWYiQtLqHtEiXmIY92vIOOLqA sw+p8lDtPlpSpOCo6STc40T4j4ymvTQ8miSZNMQeBBBm5EA7WucrIMgYeH8wuuM/DG +BfgFttLkbWWOmkrZgLyIIMf/YZnzRxDgoxY8eXn76fo0NBew4JbrSvc+cRNfaFiAl QkEWcPh0v2r3CBUEUYOst7UeoaOyYdLc4pb1uRmVVT2l0puoiHyRr+BB00fdwvDOte zMTrahakOeCUcuHDF8D2CjLZFngzAzI+3HVShn15UKErn1OlTsiT38Xn3cVrzIAtYv 8z5PR0qB8xmPA== Message-ID: <8705aa4f-5e02-45e7-ad45-0baa982a8c02@kernel.org> Date: Fri, 18 Sep 2026 09:08:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [SLUB] nfs_page cmpxchg_double_fail and perf lock perturbation on dual-socket NFS/RDMA Content-Language: en-US To: Tim Menninger , Harry Yoo Cc: 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 References: <20260917162533.600472-1-tmenninger@everpuredata.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4522C1C0003 X-Stat-Signature: z7dotsmiarit6zzdfdntxp1mh8f4f9qn X-Rspam-User: X-HE-Tag: 1789715325-942635 X-HE-Meta: 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 TjYlpYmz MvbRlkuBYiOQpXgK6IHQDimgXBjBQ02K2ks8zY/gYLq9F9mCFGcQMflW0V74ToHUNI7fBkoIJf3r6OyzeG9geM06sNKRlMe3OC7gfTVFUKdTALMyKnYeHu2XDNDk+0JoF2sAdG35sET6SQxCFT88A9ehDZaBEjrbp89UWYhiyRVES6BQzf4c9723gmmkg07PJnHNx9mAh/RwRc+BYKQFVFfAQAAGCkinB7kZqjRq+J5YigvKkntvlRQlfya2kerQe6OOKnvmWHjLY3uZf6lFVM59aUr79fR/Vs0s59qdquHEpmX76nw900Qy+aQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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? > Thanks, > Tim