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Thu, 26 Feb 2026 12:04:24 +0000 (GMT) Date: Thu, 26 Feb 2026 13:04:22 +0100 From: Heiko Carstens To: Mathieu Desnoyers Cc: Andrew Morton , linux-kernel@vger.kernel.org, "Paul E. McKenney" , Steven Rostedt , Masami Hiramatsu , Dennis Zhou , Tejun Heo , Christoph Lameter , Martin Liu , David Rientjes , christian.koenig@amd.com, Shakeel Butt , SeongJae Park , Michal Hocko , Johannes Weiner , Sweet Tea Dorminy , Lorenzo Stoakes , "Liam R . Howlett" , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , Christian Brauner , Wei Yang , David Hildenbrand , Miaohe Lin , Al Viro , linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, Yu Zhao , Roman Gushchin , Mateusz Guzik , Matthew Wilcox , Baolin Wang , Aboorva Devarajan , Vasily Gorbik , linux-s390@vger.kernel.org Subject: Re: [PATCH v17 0/3] Improve proc RSS accuracy Message-ID: <20260226120422.8101Cc2-hca@linux.ibm.com> References: <20260217161006.1105611-1-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260217161006.1105611-1-mathieu.desnoyers@efficios.com> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=TNRIilla c=1 sm=1 tr=0 ts=69a036ce cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=kj9zAlcOel0A:10 a=HzLeVaNsDn8A:10 a=VkNPw1HP01LnGYTKEx00:22 a=Mpw57Om8IfrbqaoTuvik:22 a=GgsMoib0sEa3-_RKJdDe:22 a=VwQbUJbxAAAA:8 a=7d_E57ReAAAA:8 a=Z4Rwk6OoAAAA:8 a=Z2se5BRXh4BkGdnmWtwA:9 a=CjuIK1q_8ugA:10 a=jhqOcbufqs7Y1TYCrUUU:22 a=HkZW87K1Qel5hWWM3VKY:22 X-Proofpoint-GUID: tD1VGSP6HieBCF5wEAHv0bKZIDdXK7aS X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjI2MDEwNSBTYWx0ZWRfXxnBFMIMGvx93 NdpWAzHcd9kNIM7tpzuPDi3BSVm5oNJyX6k7U0zZdM32iWRNeKiIIDNyDwhW1ie1R6T7aYFi1O/ 4fTTnuaMtg+xKW1e1SAZWgaAArbF6sYmYRLl0D+MSZtAg1edED7r4cnXS7CPaeMF9mzXf9faZ1z qpQdHAJooVMDsMDGOkFzgtGitkCuFBpyeTRc6t74i/nwBL9/4KpF6bQ7on4XWzxPvWRijLBIcOv ujVTdWIdcqGk/3fdev5KpkuWBOoop05s2VqEGRalxYfMIHqrcIup+G8zDyxRelcgxsGbr8FC8Cj X9bx/fneQd6kt42vykx7myCLplIrWu/25T3vAdeEcbCbhHiXItBLsdtoAwUQ0/+Im47jQZbTkhT wN+y90PoLt8pSiXfN5aITpdmy7OKN6jXjHJTn2mvgLfS6k6L2dfKdg7fXZsMgJL27bQk0EH3CkN 9JG/g+VOAbbevvP5dag== X-Proofpoint-ORIG-GUID: 8HrdOn9qyY5RT1ScPmZUbcFIKf-LaGiO X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-25_04,2026-02-25_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 suspectscore=0 adultscore=0 priorityscore=1501 impostorscore=0 spamscore=0 clxscore=1011 bulkscore=0 lowpriorityscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2601150000 definitions=main-2602260105 X-Rspam-User: X-Stat-Signature: d89x43bg3m3ry6sry6y8575se68oroun X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A53681C0019 X-HE-Tag: 1772107497-9817 X-HE-Meta: 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 KteGTuYa n+6Su9gM+4kMlDsdIEWT8aRdqdeGLuwBfO0o5LzhEpQSLPWJ/jl6+c/sjg6FAqE+b0g3K2sXH1B/oL50WCsP+UVmodhMKoXHVdcgEJrVoxSvdSFYJtK6WYcgV4Mafb7xT5FS8DYQyyu+t/28CvKxbWOu6BbDnit+cjdxTZcn1/ScvZSzNUJA6sK6JFYPqFj4YPE7sRSV5/+r0m9cGI152iGgVrGffundBHPpBwaJyhHH0aQKE9+hKwGLyYxDAjtbYLxWpjq0Kul+kNKV5kdtq7KfWmYmmGYlYK91BGZcUV5oq7me+FcaM8W9mXuMt0zcoyN1InSXyVvi1FsvVkVix5djWwTRTTIdDIaopnGQnHdKKMJHNQM10kyUopVpGymcRyUQCoNmoa23h6PYerC+BRzKgdVNob7y+QbSWvMhNNt8MAAbCyeMTxHACOg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Feb 17, 2026 at 11:10:03AM -0500, Mathieu Desnoyers wrote: > This series introduces the hierarchical tree counter (hpcc) to increase > accuracy of approximated RSS counters exposed through proc interfaces. > > With a test program hopping across CPUs doing frequent mmap/munmap > operations, the upstream implementation approximation reaches a 1GB > delta from the precise value after a few minutes, compared to a 80MB > delta with the hierarchical counter. The hierarchical counter provides a > guaranteed maximum approximation inaccuracy of 192MB on that hardware > topology. > > This series is based on > commit 0f2acd3148e0 Merge tag 'm68knommu-for-v7.0' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu > > The main changes since v16: > - Dropped OOM killer 2-pass task selection algorithm. > - Introduce Kunit tests. > - Only perform atomic increments of intermediate tree nodes when > bits which are significant for carry propagation are being changed. This seems to cause crashes with linux-next on s390, at least I could bisect it to the last patch of this series. Reverting the last one, makes the crashes go away: 0acac6604c1cfd7a1762901f0a4abe87cf3a8619 is the first bad commit commit 0acac6604c1cfd7a1762901f0a4abe87cf3a8619 (HEAD) Author: Mathieu Desnoyers AuthorDate: Tue Feb 17 11:10:06 2026 -0500 Commit: Andrew Morton CommitDate: Tue Feb 24 11:15:15 2026 -0800 mm: improve RSS counter approximation accuracy for proc interfaces Unable to handle kernel pointer dereference in virtual kernel address space Failing address: 766d615f72615000 TEID: 766d615f72615803 ESOP-2 FSI Fault in home space mode while using kernel ASCE. AS:000000025dc04007 R3:0000000000000024 Oops: 0038 ilc:2 [#1]SMP Modules linked in: CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.0.0-20260224.rc1.git266.3ef088b0c577.300.fc43.s390x+next #1 PREEMPTLAZY Hardware name: IBM 3931 A01 703 (z/VM 7.4.0) Krnl PSW : 0704c00180000000 00000216ef164cde (kernfs_name_hash+0x1e/0xb0) R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3 Krnl GPRS: 0000000000000000 0000000000000000 766d615f72615f65 0000000000000000 766d615f72615f65 0000000000000000 0000000000000000 0000000000000000 766d615f72615f65 0000000081212440 0000000000000000 0000000000000000 0000000080a00000 00000216efcb5390 00000216ef16530c 00000196eeb07ae0 Krnl Code: 00000216ef164cd2: a7190000 lghi %r1,0 00000216ef164cd6: b9040042 lgr %r4,%r2 *00000216ef164cda: a7090000 lghi %r0,0 >00000216ef164cde: b25e0014 srst %r1,%r4 00000216ef164ce2: a714fffe brc 1,00000216ef164cde 00000216ef164ce6: b9e92051 sgrk %r5,%r1,%r2 00000216ef164cea: ec1200208076 crj %r1,%r2,8,00000216ef164d2a 00000216ef164cf0: b9160005 llgfr %r0,%r5 Call Trace: [<00000216ef164cde>] kernfs_name_hash+0x1e/0xb0 [<00000216ef167d32>] kernfs_remove_by_name_ns+0x72/0x120 [<00000216ef16bbfa>] remove_files+0x4a/0x90 [<00000216ef16bf96>] create_files+0x276/0x2b0 [<00000216ef16c15a>] internal_create_group+0x18a/0x320 [<00000216f09b61c6>] swap_init+0x5e/0xa0 [<00000216eec7fb00>] do_one_initcall+0x40/0x270 [<00000216f0990a40>] kernel_init_freeable+0x2b0/0x330 [<00000216efb5160e>] kernel_init+0x2e/0x180 [<00000216eec81ffc>] __ret_from_fork+0x3c/0x240 [<00000216efb5e052>] ret_from_fork+0xa/0x30 Last Breaking-Event-Address: [<00000216ef165306>] kernfs_find_ns+0x76/0x140 Kernel panic - not syncing: Fatal exception: panic_on_oops