Re: [PATCH v2 2/3] arm64: mm: Optimize range_split_to_ptes()
From: Yang Shi <hidden>
Date: 2025-11-06 20:47:35
Also in:
lkml
On 11/6/25 8:09 AM, Ryan Roberts wrote:
Enter lazy_mmu mode while splitting a range of memory to pte mappings.
This causes barriers, which would otherwise be emitted after every pte
(and pmd/pud) write, to be deferred until exiting lazy_mmu mode.
For large systems, this is expected to significantly speed up fallback
to pte-mapping the linear map for the case where the boot CPU has
BBML2_NOABORT, but secondary CPUs do not. I haven't directly measured
it, but this is equivalent to commit 1fcb7cea8a5f ("arm64: mm: Batch dsb
and isb when populating pgtables").
Note that for the path from arch_kfence_init_pool(), we may sleep while
allocating memory inside the lazy_mmu mode. Sleeping is not allowed by
generic code inside lazy_mmu, but we know that the arm64 implementation
is sleep-safe. So this is ok and follows the same pattern already used
by split_kernel_leaf_mapping().
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>Reviewed-by: Yang Shi <redacted> Thanks, Yang
quoted hunk ↗ jump to hunk
--- arch/arm64/mm/mmu.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index a364ac2c9c61..652bb8c14035 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c@@ -832,8 +832,14 @@ static const struct mm_walk_ops split_to_ptes_ops = { static int range_split_to_ptes(unsigned long start, unsigned long end, gfp_t gfp) { - return walk_kernel_page_table_range_lockless(start, end, + int ret; + + arch_enter_lazy_mmu_mode(); + ret = walk_kernel_page_table_range_lockless(start, end, &split_to_ptes_ops, NULL, &gfp); + arch_leave_lazy_mmu_mode(); + + return ret; } static bool linear_map_requires_bbml2 __initdata;