On 19/12/25 09:45, Ritesh Harjani (IBM) wrote:
Sourabh Jain <[email protected]> writes:
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
And that every other architecture will have to duplicate this in their
arch_hugetlb_valid_size() whenever they face the same problem.
Instead like at other places, hugepages_supported() should also be
checked in the following cmdlines setup functions.
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.
Right. Thanks for taking care of it. I guess after this patch [1] moves
hugetlbpage_init_defaultsize() to mmu_early_init_devtree(), it's good to
bring back these checks in the respective cmdline setup functions which
was removed as part of commit [2]
[1]:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2354ad252b66695be02f4acd18e37bf6264f0464
[2]:
https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c2833a5bf75b3657c4dd20b3709c8c702754cb1f
LGTM. Please feel free to add:
Reviewed-by: Ritesh Harjani (IBM) <[email protected]>
Thank you for the review Ritesh.
- Sourabh Jain
