On Mon, Jul 17, 2023 at 03:31:09PM +0100, Ryan Roberts wrote:
> +/*
> + * folio_remove_rmap_range - take down pte mappings from a range of pages
> + * belonging to a folio. All pages are accounted as small pages.
> + * @folio: folio that all pages belong to
> + * @page: first page in range to remove mapping from
> + * @nr: number of pages in range to remove mapping from
> + * @vma: the vm area from which the mapping is removed
> + *
> + * The caller needs to hold the pte lock.
> + */
This could stand a little reworking. How about this?
/**
* folio_remove_rmap_range - Take down PTE mappings from a range of pages.
* @folio: Folio containing all pages in range.
* @page: First page in range to unmap.
* @nr: Number of pages to unmap.
* @vma: The VM area containing the range.
*
* All pages in the range must belong to the same VMA & folio. They
* must be mapped with PTEs, not a PMD.
*
* Context: Caller holds the pte lock.
*/
> +void folio_remove_rmap_range(struct folio *folio, struct page *page,
> + int nr, struct vm_area_struct *vma)
> +{
> + atomic_t *mapped = &folio->_nr_pages_mapped;
> + int nr_unmapped = 0;
> + int nr_mapped;
> + bool last;
> + enum node_stat_item idx;
> +
> + if (unlikely(folio_test_hugetlb(folio))) {
> + VM_WARN_ON_FOLIO(1, folio);
> + return;
> + }
> +
> + if (!folio_test_large(folio)) {
> + /* Is this the page's last map to be removed? */
> + last = atomic_add_negative(-1, &page->_mapcount);
> + nr_unmapped = last;
> + } else {
> + for (; nr != 0; nr--, page++) {
> + /* Is this the page's last map to be removed? */
> + last = atomic_add_negative(-1, &page->_mapcount);
> + if (last) {
> + /* Page still mapped if folio mapped entirely */
> + nr_mapped = atomic_dec_return_relaxed(mapped);
We're still doing one atomic op per page on the folio's nr_pages_mapped
... is it possible to batch this and use atomic_sub_return_relaxed()?
