Commit 070e807c authored by Matthew Wilcox's avatar Matthew Wilcox
Browse files

page cache: Convert filemap_map_pages to XArray 



Slight change of strategy here; if we have trouble getting hold of a
page for whatever reason (eg a compound page is split underneath us),
don't spin to stabilise the page, just continue the iteration, like we
would if we failed to trylock the page.  Since this is a speculative
optimisation, it feels like we should allow the process to take an extra
fault if it turns out to need this page instead of spending time to pin
down a page it may not need.

Signed-off-by: default avatarMatthew Wilcox <willy@infradead.org>
parent c1901cd3

mm/filemap.c

+13 −29
Original line number Diff line number Diff line
@@ -2516,45 +2516,31 @@ EXPORT_SYMBOL(filemap_fault); 
void filemap_map_pages(struct vm_fault *vmf,

		pgoff_t start_pgoff, pgoff_t end_pgoff)

{

	struct radix_tree_iter iter;

	void **slot;

	struct file *file = vmf->vma->vm_file;

	struct address_space *mapping = file->f_mapping;

	pgoff_t last_pgoff = start_pgoff;

	unsigned long max_idx;

	XA_STATE(xas, &mapping->i_pages, start_pgoff);

	struct page *head, *page;



	rcu_read_lock();

	radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start_pgoff) {

		if (iter.index > end_pgoff)

			break;

repeat:

		page = radix_tree_deref_slot(slot);

		if (unlikely(!page))

			goto next;

		if (radix_tree_exception(page)) {

			if (radix_tree_deref_retry(page)) {

				slot = radix_tree_iter_retry(&iter);

	xas_for_each(&xas, page, end_pgoff) {

		if (xas_retry(&xas, page))

			continue;

			}

		if (xa_is_value(page))

			goto next;

		}



		head = compound_head(page);

		if (!page_cache_get_speculative(head))

			goto repeat;

			goto next;



		/* The page was split under us? */

		if (compound_head(page) != head) {

			put_page(head);

			goto repeat;

		}

		if (compound_head(page) != head)

			goto skip;



		/* Has the page moved? */

		if (unlikely(page != *slot)) {

			put_page(head);

			goto repeat;

		}

		if (unlikely(page != xas_reload(&xas)))

			goto skip;



		if (!PageUptodate(page) ||

				PageReadahead(page) ||
@@ -2573,10 +2559,10 @@ repeat: 
		if (file->f_ra.mmap_miss > 0)

			file->f_ra.mmap_miss--;



		vmf->address += (iter.index - last_pgoff) << PAGE_SHIFT;

		vmf->address += (xas.xa_index - last_pgoff) << PAGE_SHIFT;

		if (vmf->pte)

			vmf->pte += iter.index - last_pgoff;

		last_pgoff = iter.index;

			vmf->pte += xas.xa_index - last_pgoff;

		last_pgoff = xas.xa_index;

		if (alloc_set_pte(vmf, NULL, page))

			goto unlock;

		unlock_page(page);
@@ -2589,8 +2575,6 @@ next: 
		/* Huge page is mapped? No need to proceed. */

		if (pmd_trans_huge(*vmf->pmd))

			break;

		if (iter.index == end_pgoff)

			break;

	}

	rcu_read_unlock();

}

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