[PATCH v2] powerpc/hugetlb: Disable gigantic hugepages if fadump is active

Sourabh Jain sourabhjain at linux.ibm.com
Fri Jan 24 21:32:20 AEDT 2025


The fadump kernel boots with limited memory solely to collect the kernel
core dump. Having gigantic hugepages in the fadump kernel is of no use.
Many times, the fadump kernel encounters OOM (Out of Memory) issues if
gigantic hugepages are allocated.

To address this, disable gigantic hugepages if fadump is active by
returning early from arch_hugetlb_valid_size() using
hugepages_supported(). hugepages_supported() returns false if fadump is
active.

Returning early from arch_hugetlb_valid_size() not only disables
gigantic hugepages but also avoids unnecessary hstate initialization for
every hugepage size supported by the platform.

kernel logs related to hugepages with this patch included:
kernel argument passed: hugepagesz=1G hugepages=1

First kernel: gigantic hugepage got allocated
==============================================

dmesg | grep -i "hugetlb"
-------------------------
HugeTLB: registered 1.00 GiB page size, pre-allocated 1 pages
HugeTLB: 0 KiB vmemmap can be freed for a 1.00 GiB page
HugeTLB: registered 2.00 MiB page size, pre-allocated 0 pages
HugeTLB: 0 KiB vmemmap can be freed for a 2.00 MiB page

$ cat /proc/meminfo | grep -i "hugetlb"
-------------------------------------
Hugetlb:         1048576 kB

Fadump kernel: gigantic hugepage not allocated
===============================================

dmesg | grep -i "hugetlb"
-------------------------
[    0.000000] HugeTLB: unsupported hugepagesz=1G
[    0.000000] HugeTLB: hugepages=1 does not follow a valid hugepagesz, ignoring
[    0.706375] HugeTLB support is disabled!
[    0.773530] hugetlbfs: disabling because there are no supported hugepage sizes

$ cat /proc/meminfo | grep -i "hugetlb"
----------------------------------
<Nothing>

Cc: Hari Bathini <hbathini at linux.ibm.com>
Cc: Madhavan Srinivasan <maddy at linux.ibm.com>
Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Ritesh Harjani (IBM)" <ritesh.list at gmail.com>
Signed-off-by: Sourabh Jain <sourabhjain at linux.ibm.com>
---

Changelog:

v1:
https://lore.kernel.org/all/20250121150419.1342794-1-sourabhjain@linux.ibm.com/

v2:
 - disable gigantic hugepage in arch code, arch_hugetlb_valid_size()

---
 arch/powerpc/mm/hugetlbpage.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 6b043180220a..087a8df32416 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -135,8 +135,12 @@ int __init alloc_bootmem_huge_page(struct hstate *h, int nid)
 
 bool __init arch_hugetlb_valid_size(unsigned long size)
 {
-	int shift = __ffs(size);
-	int mmu_psize;
+	int shift, mmu_psize;
+
+	if (!hugepages_supported())
+		return false;
+
+	shift = __ffs(size);
 
 	/* Check that it is a page size supported by the hardware and
 	 * that it fits within pagetable and slice limits. */
-- 
2.48.1



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