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Thu, 18 Dec 2025 13:06:51 GMT Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 58C302004B; Thu, 18 Dec 2025 13:06:51 +0000 (GMT) Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BC06A20040; Thu, 18 Dec 2025 13:06:47 +0000 (GMT) Received: from [9.39.19.14] (unknown [9.39.19.14]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 18 Dec 2025 13:06:47 +0000 (GMT) Message-ID: <1fddcf72-26f7-4fb4-84b8-1328e486d58e@linux.ibm.com> Date: Thu, 18 Dec 2025 18:36:46 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5] mm/hugetlb: ignore hugepage kernel args if hugepages are unsupported To: "David Hildenbrand (Red Hat)" , linux-kernel@vger.kernel.org Cc: Andrew Morton , Borislav Petkov , Christophe Leroy , Heiko Carstens , Ingo Molnar , Madhavan Srinivasan , Michael Ellerman , Muchun Song , Oscar Salvador , "Ritesh Harjani (IBM)" , Thomas Gleixner , Vasily Gorbik , linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, x86@kernel.org, linux-arm64@lists.infradead.org, linux-riscv@lists.infradead.org References: <20251218114154.228484-1-sourabhjain@linux.ibm.com> <83920c44-47f5-4a46-bfa7-76713197d7e4@kernel.org> Content-Language: en-US From: Sourabh Jain In-Reply-To: <83920c44-47f5-4a46-bfa7-76713197d7e4@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: IOMjxDdqC_INVd8pD7lbLmjPG0vfkoRD X-Authority-Analysis: v=2.4 cv=CLgnnBrD c=1 sm=1 tr=0 ts=6943fc70 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=wP3pNCr1ah4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=GZ12N8NoI2vug0DTctEA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: rGJZSZAJBQua-nl0FXSZ6hN3il9LBdnD X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMjEzMDAwOSBTYWx0ZWRfX81IRjmUONXph vRAcgAYV2crAU/QbOJ7+PfueA+I8tNHkip0kvKVvQuphwhyC7oqrgSAukbSdpdjxuNYI5umCGCf K5+w/qkxfOWhS8HgN14q7okSGpEUZPEtvWx8GpHcGsHSgXZ/Shnj02rFvKJO0xre4+CKtuCEoiP dB/GPOCFuV2MF7RA2vZ/lJCBgpIf0a6AsuMAiXDOksBsJQAZ6BxUndMDhkNRxtGXrQ+5MRzP/f0 AAzNUoSX1crFlsF+mhqU6AVJ7Lzod1K8N/ryvc5l/6RHwdO7me0NDg3htWywFTtQjNefRZQ5SKC ikJN5U/o/W0IHViZx/Iiyjg/YIxIUhQ4Nw1yEeALa1D+Ehzv78TUPYuXU8Z2O09tp4XTChyShNV qpiBfzUVNwRMF7hOaLwoM49FW/BVRA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-12-18_01,2025-12-17_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 clxscore=1015 lowpriorityscore=0 malwarescore=0 suspectscore=0 phishscore=0 priorityscore=1501 bulkscore=0 impostorscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2512130009 On 18/12/25 17:32, David Hildenbrand (Red Hat) wrote: > On 12/18/25 12:41, Sourabh Jain wrote: >> Skip processing hugepage kernel arguments (hugepagesz, hugepages, and >> default_hugepagesz) when hugepages are not supported by the >> architecture. >> >> Some architectures may need to disable hugepages based on conditions >> discovered during kernel boot. The hugepages_supported() helper allows >> architecture code to advertise whether hugepages are supported. >> >> Currently, normal hugepage allocation is guarded by >> hugepages_supported(), but gigantic hugepages are allocated regardless >> of this check. This causes problems on powerpc for fadump (firmware- >> assisted dump). >> >> In the fadump (firmware-assisted dump) scenario, a production kernel >> crash causes the system to boot into a special kernel whose sole >> purpose is to collect the memory dump and reboot. Features such as >> hugepages are not required in this environment and should be >> disabled. >> >> For example, fadump kernel booting with the kernel arguments >> default_hugepagesz=1GB hugepagesz=1GB hugepages=200 prints the >> following logs: >> >> HugeTLB: allocating 200 of page size 1.00 GiB failed.  Only allocated >> 58 hugepages. >> HugeTLB support is disabled! >> HugeTLB: huge pages not supported, ignoring associated command-line >> parameters >> hugetlbfs: disabling because there are no supported hugepage sizes >> >> Even though the logs say that hugetlb support is disabled, gigantic >> hugepages are still getting allocated, which causes the fadump kernel >> to run out of memory during boot. > > Yeah, that's suboptimal. > >> >> To fix this, the gigantic hugepage allocation should come under >> hugepages_supported(). >> >> To bring gigantic hugepage allocation under hugepages_supported(), two >> approaches were previously proposed: >> [1] Check hugepages_supported() in the generic code before allocating >> gigantic hugepages. >> [2] Make arch_hugetlb_valid_size() return false for all hugetlb sizes. >> >> Approach [2] has two minor issues: >> 1. It prints misleading logs about invalid hugepage sizes >> 2. The kernel still processes hugepage kernel arguments unnecessarily >> >> To control gigantic hugepage allocation, it is proposed to skip >> processing the hugepage kernel arguments (hugepagesz, hugepages, and >> default_hugepagesz) when hugepages_support() returns false. > > You could briefly mention the new output here, so one has a > before-after comparison. Here is the fadump kernel boot logs after this patch applied: kernel command had: default_hugepagesz=1GB hugepagesz=1GB hugepages=200 HugeTLB: hugepages unsupported, ignoring default_hugepagesz=1GB cmdline HugeTLB: hugepages unsupported, ignoring hugepagesz=1GB cmdline HugeTLB: hugepages unsupported, ignoring hugepages=200 cmdline HugeTLB support is disabled! hugetlbfs: disabling because there are no supported hugepage sizes I will wait for a day or two before sending v2 with the above logs included in the commit message. > > Curious, should we at least add a Fixes: tag? Allocating memory when > it's completely unusable sounds wrong. Not sure which commit I should use for Fixes. This issue has been present for a long time, possibly since the beginning. I also noticed an interesting issue related to excessive memory allocation, where the production/first kernel failed to boot. While testing this patch, I configured a very high hugepages (hugepagesz=2M) count, and the first kernel failed to boot as a result. I will report this issue separately. > > [...] > >> +    if (!hugepages_supported()) { >> +        pr_warn("HugeTLB: hugepages unsupported, ignoring >> default_hugepagesz=%s cmdline\n", >> +            s); >> +        return 0; >> +    } >> + >>       parsed_valid_hugepagesz = false; >>       if (parsed_default_hugepagesz) { >>           pr_err("HugeTLB: default_hugepagesz previously specified, >> ignoring %s\n", s); > > > LGTM! > > Acked-by: David Hildenbrand (Red Hat) > Thanks for the Ack David. - Sourabh Jain