Re: [PATCH 1/4] mm: Trial do_wp_page() simplification

Oleg Nesterov
2020-09-15T22:59:40Z

On 08/21, Peter Xu wrote:
>
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2927,50 +2927,25 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
> * not dirty accountable.
> */
> if (PageAnon(vmf->page)) {
> - int total_map_swapcount;
> - if (PageKsm(vmf->page) && (PageSwapCache(vmf->page) ||
> - page_count(vmf->page) != 1))
> + struct page *page = vmf->page;
> +
> + /* PageKsm() doesn't necessarily raise the page refcount */
> + if (PageKsm(page) || page_count(page) != 1)
> + goto copy;
> + if (!trylock_page(page))
> + goto copy;
> + if (PageKsm(page) || page_mapcount(page) != 1 || page_count(page) != 1) {
> + unlock_page(page);
> goto copy;
> - if (!trylock_page(vmf->page)) {
> - get_page(vmf->page);
> - pte_unmap_unlock(vmf->pte, vmf->ptl);
> - lock_page(vmf->page);
> - vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
> - vmf->address, &vmf->ptl);
> - if (!pte_same(*vmf->pte, vmf->orig_pte)) {
> - update_mmu_tlb(vma, vmf->address, vmf->pte);
> - unlock_page(vmf->page);
> - pte_unmap_unlock(vmf->pte, vmf->ptl);
> - put_page(vmf->page);
> - return 0;
> - }
> - put_page(vmf->page);
> - }
> - if (PageKsm(vmf->page)) {
> - bool reused = reuse_ksm_page(vmf->page, vmf->vma,
> - vmf->address);
> - unlock_page(vmf->page);
> - if (!reused)
> - goto copy;
> - wp_page_reuse(vmf);
> - return VM_FAULT_WRITE;
> - }
> - if (reuse_swap_page(vmf->page, &total_map_swapcount)) {

It seems that nobody else calls reuse_swap_page() with total_map_swapcount != NULL.

Oleg.