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Commit e791f407 authored by Linus Torvalds's avatar Linus Torvalds Committed by Todd Kjos
Browse files

BACKPORT: mm: do_wp_page() simplification 



How about we just make sure we're the only possible valid user fo the
page before we bother to reuse it?

Simplify, simplify, simplify.

And get rid of the nasty serialization on the page lock at the same time.

[peterx: add subject prefix]

Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarPeter Xu <peterx@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 09854ba94c6aad7886996bfbee2530b3d8a7f4f4)

[Kalesh Singh: Resolve conflict in mm/memory.c]
Bug: 176847924
Signed-off-by: default avatarKalesh Singh <kaleshsingh@google.com>
Change-Id: I0b855b305332564670b8cbea9660405fed89a044
parent fb8e4568

mm/memory.c

+17 −41
Original line number Diff line number Diff line
@@ -2723,49 +2723,25 @@ 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(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)) {

				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)

		if (!trylock_page(page))

			goto copy;

		if (PageKsm(page) || page_mapcount(page) != 1 || page_count(page) != 1) {

			unlock_page(page);

			goto copy;

			wp_page_reuse(vmf);

			return VM_FAULT_WRITE;

		}

		if (reuse_swap_page(vmf->page, &total_map_swapcount)) {

			if (total_map_swapcount == 1) {

		/*

				 * The page is all ours. Move it to

				 * our anon_vma so the rmap code will

				 * not search our parent or siblings.

				 * Protected against the rmap code by

				 * the page lock.

		 * Ok, we've got the only map reference, and the only

		 * page count reference, and the page is locked,

		 * it's dark out, and we're wearing sunglasses. Hit it.

		 */

				page_move_anon_rmap(vmf->page, vma);

			}

			unlock_page(vmf->page);

		wp_page_reuse(vmf);

		unlock_page(page);

		return VM_FAULT_WRITE;

		}

		unlock_page(vmf->page);

	} else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==

					(VM_WRITE|VM_SHARED))) {

		return wp_page_shared(vmf);