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Message-ID: <20251218114154.228484-1-sourabhjain@linux.ibm.com>
Date: Thu, 18 Dec 2025 17:11:54 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: Sourabh Jain <sourabhjain@...ux.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Borislav Petkov <bp@...en8.de>,
Christophe Leroy <christophe.leroy@...roup.eu>,
David Hildenbrand <david@...nel.org>,
Heiko Carstens <hca@...ux.ibm.com>, Ingo Molnar <mingo@...hat.com>,
Madhavan Srinivasan <maddy@...ux.ibm.com>,
Michael Ellerman <mpe@...erman.id.au>,
Muchun Song <muchun.song@...ux.dev>,
Oscar Salvador <osalvador@...e.de>,
"Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
Vasily Gorbik <gor@...ux.ibm.com>, linux-mm@...ck.org,
linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
x86@...nel.org, linux-arm64@...ts.infradead.org,
linux-riscv@...ts.infradead.org
Subject: [PATCH v5] mm/hugetlb: ignore hugepage kernel args if hugepages are unsupported
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.
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.
Link: https://lore.kernel.org/all/20250121150419.1342794-1-sourabhjain@linux.ibm.com/ [1]
Link: https://lore.kernel.org/all/20250128043358.163372-1-sourabhjain@linux.ibm.com/ [2]
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: David Hildenbrand <david@...nel.org>
Cc: Heiko Carstens <hca@...ux.ibm.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Muchun Song <muchun.song@...ux.dev>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Ritesh Harjani (IBM) <ritesh.list@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vasily Gorbik <gor@...ux.ibm.com>
Cc: linux-mm@...ck.org
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: linux-s390@...r.kernel.org
Cc: x86@...nel.org
Cc: linux-arm64@...ts.infradead.org
Cc: linux-riscv@...ts.infradead.org
Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
---
Changelog:
v1:
https://lore.kernel.org/all/20250121150419.1342794-1-sourabhjain@linux.ibm.com/
v2:
https://lore.kernel.org/all/20250124103220.111303-1-sourabhjain@linux.ibm.com/
- disable gigantic hugepage in arch code, arch_hugetlb_valid_size()
v3:
https://lore.kernel.org/all/20250125104928.88881-1-sourabhjain@linux.ibm.com/
- Do not modify the initialization of the shift variable
v4:
https://lore.kernel.org/all/20250128043358.163372-1-sourabhjain@linux.ibm.com/
- Update commit message to include how hugepages_supported() detects
hugepages support when fadump is active
- Add Reviewed-by tag
- NO functional change
v5:
- Significant change in approach: disable processing of hugepage kernel
arguments if hugepages_supported() returns false
- Drop a Reviewed-by tag
---
mm/hugetlb.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 51273baec9e5..e0ab14020513 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4286,6 +4286,11 @@ static int __init hugepages_setup(char *s)
unsigned long tmp;
char *p = s;
+ if (!hugepages_supported()) {
+ pr_warn("HugeTLB: hugepages unsupported, ignoring hugepages=%s cmdline\n", s);
+ return 0;
+ }
+
if (!parsed_valid_hugepagesz) {
pr_warn("HugeTLB: hugepages=%s does not follow a valid hugepagesz, ignoring\n", s);
parsed_valid_hugepagesz = true;
@@ -4366,6 +4371,11 @@ static int __init hugepagesz_setup(char *s)
unsigned long size;
struct hstate *h;
+ if (!hugepages_supported()) {
+ pr_warn("HugeTLB: hugepages unsupported, ignoring hugepagesz=%s cmdline\n", s);
+ return 0;
+ }
+
parsed_valid_hugepagesz = false;
size = (unsigned long)memparse(s, NULL);
@@ -4414,6 +4424,12 @@ static int __init default_hugepagesz_setup(char *s)
unsigned long size;
int i;
+ 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);
--
2.51.1
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