mm: consistent truncate and invalidate loops

Make the pagevec_lookup loops in truncate_inode_pages_range(),
invalidate_mapping_pages() and invalidate_inode_pages2_range() more
consistent with each other.

They were relying upon page->index of an unlocked page, but apologizing
for it: accept it, embrace it, add comments and WARN_ONs, and simplify the
index handling.

invalidate_inode_pages2_range() had special handling for a wrapped
page->index + 1 = 0 case; but MAX_LFS_FILESIZE doesn't let us anywhere
near there, and a corrupt page->index in the radix_tree could cause more
trouble than that would catch.  Remove that wrapped handling.

invalidate_inode_pages2_range() uses min() to limit the pagevec_lookup
when near the end of the range: copy that into the other two, although
it's less useful than you might think (it limits the use of the buffer,
rather than the indices looked up).

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 2780be4bd493..10a171113273 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -128,6 +128,7 @@ void __delete_from_page_cache(struct page *page)
 
         radix_tree_delete(&mapping->page_tree, page->index);
         page->mapping = NULL;
+        /* Leave page->index set: truncation lookup relies upon it */
         mapping->nrpages--;
         __dec_zone_page_state(page, NR_FILE_PAGES);
         if (PageSwapBacked(page))
@@ -483,6 +484,7 @@ int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
                         spin_unlock_irq(&mapping->tree_lock);
                 } else {
                         page->mapping = NULL;
+                        /* Leave page->index set: truncation relies upon it */
                         spin_unlock_irq(&mapping->tree_lock);
                         mem_cgroup_uncharge_cache_page(page);
                         page_cache_release(page);