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Sun, 16 Aug 2026 13:07:11 +0000 (GMT) Received: from li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com (unknown [9.39.17.50]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Sun, 16 Aug 2026 13:07:11 +0000 (GMT) From: Ojaswin Mujoo To: linux-erofs@lists.ozlabs.org Cc: Gao Xiang , Chao Yu , Yue Hu , Jeffle Xu , Sandeep Dhavale , Hongbo Li , Chunhai Guo , linux-kernel@vger.kernel.org Subject: [PATCH 0/1] erofs: fix unused pcluster_pools for higher page sizes Date: Sun, 16 Aug 2026 18:37:08 +0530 Message-ID: X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: wybZggqbW3EdyCReKtdj2aNEOz3itYIM X-Authority-Analysis: v=2.4 cv=NLLlPU6g c=1 sm=1 tr=0 ts=6a81b605 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VwQbUJbxAAAA:8 a=YVvUhAtAW8BG0TNbuoAA:9 X-Proofpoint-Spam-Info: AW1haW4tMjYwODE2MDEwMyBTYWx0ZWRfX7w3gDTyYXZBg VbJXFcHHa1TyhCoVxZdIp45ePK/PJlKIiogPdVxSpX+JPxeET9YT3lePW/Rfnin3PiJvdCe8Qbb pQeqij3LDUcLip2GAFXx6VDWgEQJa0c= X-Proofpoint-ORIG-GUID: oYZ1P6jcpP6CgrixDxMdNLOZ5iAPTOwq X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE2MDEwMyBTYWx0ZWRfX6/4yMreFiWmn ETUO6/A8RW1MT7g/MRF3yJ8dC+Eo47xjYaMb8wako6zomDfKPAqAAY/+GIViGlLrMa9MP4AGh3h j8OPMnvbUMwOef3Dvd1VZnvuo+bMmHD68H7vCa5EBqUj/pAoJner+o6WbsVqLgpxSHyWlFNRSDn RgdFAMZgYt2brBHi9VnT3NiQd798VngwQoH+0kY0fPYzycTvaYfkg+zXZ3leChBnfzLVUi0a/+g BqVexRUY5BWf689LMVVk/FuF0C3m96A+8zdQCSKJRmLrkjqG5cqPo9EAC8fTeML2yxLC820ZhXs gb8H0TwpektyQz1f2It9rE1xB1KanandrGPrKo5YtVupfOgCabjN0nchJXSl2QAsknnvvD6XU9G lyoZVfWzWxf86wwXJ2AgDB7HwmNVvW5OHtkbdx6M6cOXCL5MldaEc1Phxk05IhqLmtgvzbNH9Zb oOxhbns764BSxdTxqpg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-16_03,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 spamscore=0 lowpriorityscore=0 phishscore=0 impostorscore=0 malwarescore=0 suspectscore=0 clxscore=1011 adultscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608160103 When inserting the erofs module on an older kernel with a 64K page size machine, we were running into the following dmesg followed by a stack dump (Needs, CONFIG_DEBUG_VM=y): [ 4.616501] kmem_cache of name 'erofs_pcluster-16' already exists The root cause is that on 64k page size: Z_EROFS_PCLUSTER_MAX_PAGES = 1M / 16k = 16 and, on that kernel, our logic to create the pcluster pool is as: static struct z_erofs_pcluster_slab pcluster_pool[] __read_mostly = { _PCLP(1), _PCLP(4), _PCLP(16), _PCLP(64), _PCLP(128), _PCLP(Z_EROFS_PCLUSTER_MAX_PAGES) }; so we were ending up creating kmemcaches for nr_pages= 1, 4, 16, 64, 128, and Z_EROFS_PCLUSTER_MAX_PAGES (=16, again). This caused the kmem_cache sanity check to emit the warning. When comparing with the upstream code, I noticed that this issue has been fixed as a side effect of the patch: commit 7361d1e3763baaf7b9349c576137851458ad38d1 Author: Gao Xiang Date: Mon Mar 10 17:54:59 2025 +0800 erofs: support unaligned encoded data which changes static struct z_erofs_pcluster_slab pcluster_pool[] __read_mostly = { _PCLP(1), _PCLP(4), _PCLP(16), _PCLP(64), _PCLP(128), - _PCLP(Z_EROFS_PCLUSTER_MAX_PAGES) + _PCLP(Z_EROFS_PCLUSTER_MAX_PAGES + 1) }; and hence the final cache has nr_pages = 17 and doesn't clash with the nr_pages=16 cache anymore. However, this is still incorrect as on higher page sizes like 64k we will never use nr_pages > 16 and the rest of the caches are wasted. So this patch intends to fix the issue on upstream first and if the approach looks okay, I'll send a backport for other the older affected kernels. Regards, ojaswin Ojaswin Mujoo (1): erofs: fix unused pcluster_pools for higher page sizes fs/erofs/zdata.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) -- 2.55.0