On 11/13/20 2:59 AM, Muchun Song wrote:
> On x86_64, vmemmap is always PMD mapped if the machine has hugepages
> support and if we have 2MB contiguos pages and PMD aligned. If we want
contiguous alignment
> to free the unused vmemmap pages, we have to split the huge pmd firstly.
> So we should pre-allocate pgtable to split PMD to PTE.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
> mm/hugetlb_vmemmap.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> mm/hugetlb_vmemmap.h | 12 +++++++++
> 2 files changed, 85 insertions(+)
Thanks for the cleanup.
Oscar made some other comments. I only have one additional minor comment
below.
With those minor cleanups,
Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
...
> +int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
> +{
> + unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h);
> +
> + /* Store preallocated pages on huge page lru list */
Let's expland the above comment to something like this:
/*
* Use the huge page lru list to temporarily store the preallocated
* pages. The preallocated pages are used and the list is emptied
* before the huge page is put into use. When the huge page is put
* into use by prep_new_huge_page() the list will be reinitialized.
*/
> + INIT_LIST_HEAD(&page->lru);
> +
> + while (nr--) {
> + pte_t *pte_p;
> +
> + pte_p = pte_alloc_one_kernel(&init_mm);
> + if (!pte_p)
> + goto out;
> + list_add(&virt_to_page(pte_p)->lru, &page->lru);
> + }
> +
> + return 0;
> +out:
> + vmemmap_pgtable_free(page);
> + return -ENOMEM;
> +}
--
Mike Kravetz
