Re: [PATCH v8 09/12] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap

Oscar Salvador
2020-12-10T11:42:25Z

On Thu, Dec 10, 2020 at 11:55:23AM +0800, Muchun Song wrote:
> +hugetlb_free_vmemmap
> + When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this enables freeing
> + unused vmemmap pages associated each HugeTLB page.
^^^ with

> - if (end - start < PAGES_PER_SECTION * sizeof(struct page))
> + if (is_hugetlb_free_vmemmap_enabled())
> + err = vmemmap_populate_basepages(start, end, node, NULL);
> + else if (end - start < PAGES_PER_SECTION * sizeof(struct page))
> err = vmemmap_populate_basepages(start, end, node, NULL);

Not sure if joining those in an OR makes se.se

> else if (boot_cpu_has(X86_FEATURE_PSE))
> err = vmemmap_populate_hugepages(start, end, node, altmap);
> @@ -1610,7 +1613,8 @@ void register_page_bootmem_memmap(unsigned long section_nr,
> }
> get_page_bootmem(section_nr, pud_page(*pud), MIX_SECTION_INFO);
>
> - if (!boot_cpu_has(X86_FEATURE_PSE)) {
> + if (!boot_cpu_has(X86_FEATURE_PSE) ||
> + is_hugetlb_free_vmemmap_enabled()) {

I would add a variable at the beginning called "basepages_populated"
that holds the result of those two conditions.
I am not sure if it slightly improves the code as the conditions do
not need to be rechecked, but the readibility a bit.

> +bool hugetlb_free_vmemmap_enabled;
> +
> +static int __init early_hugetlb_free_vmemmap_param(char *buf)
> +{
> + if (!buf)
> + return -EINVAL;
> +
> + /* We cannot optimize if a "struct page" crosses page boundaries. */

I think this comment belongs to the last patch.

--
Oscar Salvador
SUSE L3