mm: cleanup add_to_page_cache_locked()

Make add_to_page_cache_locked() cleaner:

 - unindent most code of the function by inverting one condition;
 - streamline code no-error path;
 - move insert error path outside normal code path;
 - call radix_tree_preload_end() earlier;

No functional changes.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -467,32 +467,34 @@ int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 	error = mem_cgroup_cache_charge(page, current->mm,
 					gfp_mask & GFP_RECLAIM_MASK);
 	if (error)
-		goto out;
+		return error;
 
 	error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
-	if (error == 0) {
+	if (error) {
+		mem_cgroup_uncharge_cache_page(page);
+		return error;
+	}
+
 	page_cache_get(page);
 	page->mapping = mapping;
 	page->index = offset;
 
 	spin_lock_irq(&mapping->tree_lock);
 	error = radix_tree_insert(&mapping->page_tree, offset, page);
-		if (likely(!error)) {
+	radix_tree_preload_end();
+	if (unlikely(error))
+		goto err_insert;
 	mapping->nrpages++;
 	__inc_zone_page_state(page, NR_FILE_PAGES);
 	spin_unlock_irq(&mapping->tree_lock);
 	trace_mm_filemap_add_to_page_cache(page);
-		} else {
+	return 0;
+err_insert:
 	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);
-		}
-		radix_tree_preload_end();
-	} else
-		mem_cgroup_uncharge_cache_page(page);
-out:
 	return error;
 }
 EXPORT_SYMBOL(add_to_page_cache_locked);