Re: [PATCH v3 0/3] A Solution to Re-enable hugetlb vmemmap optimize

Catalin Marinas
2024-01-25T18:06:25Z

On Sat, Jan 13, 2024 at 05:44:33PM +0800, Nanyong Sun wrote:
> HVO was previously disabled on arm64 [1] due to the lack of necessary
> BBM(break-before-make) logic when changing page tables.
> This set of patches fix this by adding necessary BBM sequence when
> changing page table, and supporting vmemmap page fault handling to
> fixup kernel address translation fault if vmemmap is concurrently accessed.

I'm not keen on this approach. I'm not even sure it's safe. In the
second patch, you take the init_mm.page_table_lock on the fault path but
are we sure this is unlocked when the fault was taken? Basically you can
get a fault anywhere something accesses a struct page.

How often is this code path called? I wonder whether a stop_machine()
approach would be simpler.

Andrew, I'd suggest we drop these patches from the mm tree for the time
being. They haven't received much review from the arm64 folk. Thanks.

--
Catalin