On Wed, Aug 07, 2024 at 02:46:47PM +0100, Usama Arif wrote:
> @@ -177,13 +177,56 @@ void putback_movable_pages(struct list_head *l)
> }
> }
>
> +static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
> + struct folio *folio,
> + unsigned long idx)
> +{
> + struct page *page = folio_page(folio, idx);
> + bool contains_data;
> + pte_t newpte;
> + void *addr;
> +
> + VM_BUG_ON_PAGE(PageCompound(page), page);
> + VM_BUG_ON_PAGE(!PageAnon(page), page);
> + VM_BUG_ON_PAGE(!PageLocked(page), page);
> + VM_BUG_ON_PAGE(pte_present(*pvmw->pte), page);
> +
> + if (PageMlocked(page) || (pvmw->vma->vm_flags & VM_LOCKED))
> + return false;
> +
> + /*
> + * The pmd entry mapping the old thp was flushed and the pte mapping
> + * this subpage has been non present. If the subpage is only zero-filled
> + * then map it to the shared zeropage.
> + */
> + addr = kmap_local_page(page);
> + contains_data = memchr_inv(addr, 0, PAGE_SIZE);
> + kunmap_local(addr);
> +
> + if (contains_data || mm_forbids_zeropage(pvmw->vma->vm_mm))
> + return false;
> +
> + newpte = pte_mkspecial(pfn_pte(page_to_pfn(ZERO_PAGE(pvmw->address)),
> + pvmw->vma->vm_page_prot));
Why not use my_zero_pfn() here? On many configurations this just
returns zero_pfn and avoids the indirection through mem_map.
> @@ -904,7 +958,7 @@ static int writeout(struct address_space *mapping, struct folio *folio)
> * At this point we know that the migration attempt cannot
> * be successful.
> */
> - remove_migration_ptes(folio, folio, false);
> + remove_migration_ptes(folio, folio, false, false);
bool params are not great for callsite readability.
How about a flags parameter and using names?
enum rmp_flags {
RMP_LOCKED = 1 << 0,
RMP_ZEROPAGES = 1 << 1,
}
