shmem: cleanup shmem_add_to_page_cache

shmem_add_to_page_cache() has three callsites, but only one of them wants
the radix_tree_preload() (an exceptional entry guarantees that the radix
tree node is present in the other cases), and only that site can achieve
mem_cgroup_uncharge_cache_page() (PageSwapCache makes it a no-op in the
other cases).  We did it this way originally to reflect
add_to_page_cache_locked(); but it's confusing now, so move the radix_tree
preloading and mem_cgroup uncharging to that one caller.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index 294364a24a1f62df16a2f86ca1b5f77dcc3f7aac..bd106361be4bf2d080e67f11252198c710745278 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -288,40 +288,31 @@ static int shmem_add_to_page_cache(struct page *page,
                                   struct address_space *mapping,
                                   pgoff_t index, gfp_t gfp, void *expected)
 {
-       int error = 0;
+       int error;
 
        VM_BUG_ON(!PageLocked(page));
        VM_BUG_ON(!PageSwapBacked(page));
 
+       page_cache_get(page);
+       page->mapping = mapping;
+       page->index = index;
+
+       spin_lock_irq(&mapping->tree_lock);
        if (!expected)
-               error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
+               error = radix_tree_insert(&mapping->page_tree, index, page);
+       else
+               error = shmem_radix_tree_replace(mapping, index, expected,
+                                                                page);
        if (!error) {
-               page_cache_get(page);
-               page->mapping = mapping;
-               page->index = index;
-
-               spin_lock_irq(&mapping->tree_lock);
-               if (!expected)
-                       error = radix_tree_insert(&mapping->page_tree,
-                                                       index, page);
-               else
-                       error = shmem_radix_tree_replace(mapping, index,
-                                                       expected, page);
-               if (!error) {
-                       mapping->nrpages++;
-                       __inc_zone_page_state(page, NR_FILE_PAGES);
-                       __inc_zone_page_state(page, NR_SHMEM);
-                       spin_unlock_irq(&mapping->tree_lock);
-               } else {
-                       page->mapping = NULL;
-                       spin_unlock_irq(&mapping->tree_lock);
-                       page_cache_release(page);
-               }
-               if (!expected)
-                       radix_tree_preload_end();
+               mapping->nrpages++;
+               __inc_zone_page_state(page, NR_FILE_PAGES);
+               __inc_zone_page_state(page, NR_SHMEM);
+               spin_unlock_irq(&mapping->tree_lock);
+       } else {
+               page->mapping = NULL;
+               spin_unlock_irq(&mapping->tree_lock);
+               page_cache_release(page);
        }
-       if (error)
-               mem_cgroup_uncharge_cache_page(page);
        return error;
 }
 
@@ -1202,11 +1193,18 @@ repeat:
                __set_page_locked(page);
                error = mem_cgroup_cache_charge(page, current->mm,
                                                gfp & GFP_RECLAIM_MASK);
-               if (!error)
-                       error = shmem_add_to_page_cache(page, mapping, index,
-                                               gfp, NULL);
                if (error)
                        goto decused;
+               error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
+               if (!error) {
+                       error = shmem_add_to_page_cache(page, mapping, index,
+                                                       gfp, NULL);
+                       radix_tree_preload_end();
+               }
+               if (error) {
+                       mem_cgroup_uncharge_cache_page(page);
+                       goto decused;
+               }
                lru_cache_add_anon(page);
 
                spin_lock(&info->lock);