Allocating huge pages can take a very long time on servers with terabytes of memory even when they are allocated at boot time where the allocation happens in parallel. Before this series, the kernel used a hard coded value of 2 threads per NUMA node for these allocations. This value might have been good enough in the past but it is not sufficient to fully utilize newer systems. This series changes the default so the kernel uses 25% of the available hardware threads for these allocations. In addition, we allow the user that wish to micro-optimize the allocation time to override this value via a new kernel parameter. We tested this on 2 generations of Xeon CPUs and the results show a big improvement of the overall allocation time. +-----------------------+-------+-------+-------+-------+-------+ | threads | 8 | 16 | 32 | 64 | 128 | +-----------------------+-------+-------+-------+-------+-------+ | skylake 144 cpus | 44s | 22s | 16s | 19s | 20s | | cascade lake 192 cpus | 39s | 20s | 11s | 10s | 9s | +-----------------------+-------+-------+-------+-------+-------+ On skylake, we see an improvment of 2.75x when using 32 threads, on cascade lake we can get even better at 4.3x when we use 128 threads. This speedup is quite significant and users of large machines like these should have the option to make the machines boot as fast as possible. Signed-off-by: Thomas Prescher <thomas.prescher@xxxxxxxxxxxxxxxxxxxxx> --- Changes in v2: - the default thread value has been changed from 2 threads per node to 25% of the available hardware threads - the hugepage_alloc_threads parameter now specifies the total number of threads being used instead of threads per node - the kernel now logs the time needed to allocate the huge pages and the number of threads being used - update the documentation so that users are aware that this does not apply to non-gigantic huge pages - Link to v1: https://lore.kernel.org/r/20250221-hugepage-parameter-v1-0-fa49a77c87c8@xxxxxxxxxxxxxxxxxxxxx --- Thomas Prescher (3): mm: hugetlb: improve parallel huge page allocation time mm: hugetlb: add hugetlb_alloc_threads cmdline option mm: hugetlb: log time needed to allocate hugepages Documentation/admin-guide/kernel-parameters.txt | 9 ++++ Documentation/admin-guide/mm/hugetlbpage.rst | 10 ++++ mm/hugetlb.c | 67 +++++++++++++++++++------ 3 files changed, 70 insertions(+), 16 deletions(-) --- base-commit: dd83757f6e686a2188997cb58b5975f744bb7786 change-id: 20250221-hugepage-parameter-e8542fdfc0ae Best regards, -- Thomas Prescher <thomas.prescher@xxxxxxxxxxxxxxxxxxxxx>
