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: Matthew Wilcox <willy@infradead.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index 35ae011971e153748609917594b985e21a5a1158..ae1fcaa24f97c9fdf29591849367d1ed1031809a 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -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);
-                               continue;
-                       }
+       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();
 }