mm: factor out checks and accounting from __delete_from_page_cache()

Move checks and accounting updates from __delete_from_page_cache() into
a separate function.  We will reuse it when batching page cache
truncation operations.

Link: http://lkml.kernel.org/r/20171010151937.26984-7-jack@suse.czSigned-off-by: NJan Kara <jack@suse.cz>
Acked-by: NMel Gorman <mgorman@suse.de>
Reviewed-by: NAndi Kleen <ak@linux.intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -181,17 +181,11 @@ static void page_cache_tree_delete(struct address_space *mapping,
 	mapping->nrpages -= nr;
 }
 
-/*
- * Delete a page from the page cache and free it. Caller has to make
- * sure the page is locked and that nobody else uses it - or that usage
- * is safe.  The caller must hold the mapping's tree_lock.
- */
-void __delete_from_page_cache(struct page *page, void *shadow)
+static void unaccount_page_cache_page(struct address_space *mapping,
+				      struct page *page)
 {
-	struct address_space *mapping = page->mapping;
-	int nr = hpage_nr_pages(page);
+	int nr;
 
-	trace_mm_filemap_delete_from_page_cache(page);
 	/*
 	 * if we're uptodate, flush out into the cleancache, otherwise
 	 * invalidate any existing cleancache entries.  We can't leave
@@ -228,7 +222,11 @@ void __delete_from_page_cache(struct page *page, void *shadow)
 	}
 
 	/* hugetlb pages do not participate in page cache accounting. */
-	if (!PageHuge(page)) {
+	if (PageHuge(page))
+		return;
+
+	nr = hpage_nr_pages(page);
+
 	__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
 	if (PageSwapBacked(page)) {
 		__mod_node_page_state(page_pgdat(page), NR_SHMEM, -nr);
@@ -249,9 +247,21 @@ void __delete_from_page_cache(struct page *page, void *shadow)
 	 * buddy allocator.
 	 */
 	if (WARN_ON_ONCE(PageDirty(page)))
-			account_page_cleaned(page, mapping,
-					     inode_to_wb(mapping->host));
-	}
+		account_page_cleaned(page, mapping, inode_to_wb(mapping->host));
+}
+
+/*
+ * Delete a page from the page cache and free it. Caller has to make
+ * sure the page is locked and that nobody else uses it - or that usage
+ * is safe.  The caller must hold the mapping's tree_lock.
+ */
+void __delete_from_page_cache(struct page *page, void *shadow)
+{
+	struct address_space *mapping = page->mapping;
+
+	trace_mm_filemap_delete_from_page_cache(page);
+
+	unaccount_page_cache_page(mapping, page);
 	page_cache_tree_delete(mapping, page, shadow);
 }