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>

1 files changed, 28 insertions, 30 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 294364a24a1..bd106361be4 100644
--- 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);