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Fri, 19 Dec 2025 08:21:18 GMT Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A94342004B; Fri, 19 Dec 2025 08:21:18 +0000 (GMT) Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C470420040; Fri, 19 Dec 2025 08:21:14 +0000 (GMT) Received: from [9.124.209.192] (unknown [9.124.209.192]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 19 Dec 2025 08:21:14 +0000 (GMT) Message-ID: <5acfcde7-0e8f-4228-8d9f-36b740900213@linux.ibm.com> Date: Fri, 19 Dec 2025 13:51:05 +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> <1fddcf72-26f7-4fb4-84b8-1328e486d58e@linux.ibm.com> <64a9ca24-2968-4532-ac04-594c340ec2a2@kernel.org> Content-Language: en-US From: Sourabh Jain In-Reply-To: <64a9ca24-2968-4532-ac04-594c340ec2a2@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: VMo57LUGB5mbL-L32x592RHzO_CETbAy X-Proofpoint-GUID: b35NuxmB0yfBlN4o5xEw0Ah1QGoT25Rc X-Authority-Analysis: v=2.4 cv=KrZAGGWN c=1 sm=1 tr=0 ts=69450b04 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=wP3pNCr1ah4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=icKp7thR8Zr7BtekdgcA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMjE5MDA2NyBTYWx0ZWRfX45K0c7/r6Utl KNKXLWfdlayLBssJjNgVj7rEPBSAevK6l/LaGoQ0M2OKhT5Qf9MlgqZGfC/OF8nWI4jvsFn1lQP Y1FjKKtiotAj6+SrSiT2+FmJLB8KR9khO/CWVPGQiIh8XbteCM4csCF1eNb+eKnmicpWDyTNt4r 0/lr+1AHIzsVaZEimA7fpllXp0yY5lXI7MkrRSpPn7d9bCeMGQSsnCf3dSdDSavufzEzTbdfHcm ukyIRewxefX64hHILbTZT07U3yblpXnNyxZ0NJGc2CRKEL9JXZlpkw5ruePXww8vQnH47vMbhOY n2rMYhkujHoja5eoJ0Zb8IJnb4FhM1WEyK7wHdq8EfDWrufHxeEJuRau4OWrhgD1p54MAL5XR9L K3p3GYNKwEmN3/cuHCGpKGrQwzijtEyaBS/KG7EueNliCtpNZJdMNFqpQWsFyCTDFodp0uYcJu4 ggpS+FRJEmgVlPMw/Cg== 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=2025-12-19_02,2025-12-17_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 suspectscore=0 priorityscore=1501 malwarescore=0 impostorscore=0 lowpriorityscore=0 clxscore=1015 phishscore=0 spamscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2512120000 definitions=main-2512190067 On 19/12/25 11:43, David Hildenbrand (Red Hat) wrote: > On 12/18/25 14:06, Sourabh Jain wrote: >> >> >> 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 don't know the full history, but I would assume that support for > gigantic pages was added later? > > It would be great if you could dig a bit so we could add a Fixes:. Sure, I will try to find it. > >> >> 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. > > I'd say that's rather expected: if you steal too much memory from the > kernel it will not be able to function. It's the same when using the > mem= parameter I would assume. > I reported this behavior as an issue yesterday; let's see what others think about it. https://lore.kernel.org/all/cb9f3604-8a0a-478a-8bf7-2d139ccbc89d@linux.ibm.com/ Sourabh Jain