tmpfs: convert mem_cgroup shmem to radix-swap

Remove mem_cgroup_shmem_charge_fallback(): it was only required when we
had to move swappage to filecache with GFP_NOWAIT.

Remove the GFP_NOWAIT special case from mem_cgroup_cache_charge(), by
moving its call out from shmem_add_to_page_cache() to two of thats three
callers.  But leave it doing mem_cgroup_uncharge_cache_page() on error:
although asymmetrical, it's easier for all 3 callers to handle.

These two changes would also be appropriate if anyone were to start
using shmem_read_mapping_page_gfp() with GFP_NOWAIT.

Remove mem_cgroup_get_shmem_target(): mc_handle_file_pte() can test
radix_tree_exceptional_entry() to get what it needs for itself.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 57 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5f84d2351ddb..f4ec4e7ca4cd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -35,7 +35,6 @@
 #include <linux/limits.h>
 #include <linux/mutex.h>
 #include <linux/rbtree.h>
-#include <linux/shmem_fs.h>
 #include <linux/slab.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
@@ -2873,30 +2872,6 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
                 return 0;
         if (PageCompound(page))
                 return 0;
-        /*
-         * Corner case handling. This is called from add_to_page_cache()
-         * in usual. But some FS (shmem) precharges this page before calling it
-         * and call add_to_page_cache() with GFP_NOWAIT.
-         *
-         * For GFP_NOWAIT case, the page may be pre-charged before calling
-         * add_to_page_cache(). (See shmem.c) check it here and avoid to call
-         * charge twice. (It works but has to pay a bit larger cost.)
-         * And when the page is SwapCache, it should take swap information
-         * into account. This is under lock_page() now.
-         */
-        if (!(gfp_mask & __GFP_WAIT)) {
-                struct page_cgroup *pc;
-
-                pc = lookup_page_cgroup(page);
-                if (!pc)
-                        return 0;
-                lock_page_cgroup(pc);
-                if (PageCgroupUsed(pc)) {
-                        unlock_page_cgroup(pc);
-                        return 0;
-                }
-                unlock_page_cgroup(pc);
-        }
 
         if (unlikely(!mm))
                 mm = &init_mm;
@@ -3486,31 +3461,6 @@ void mem_cgroup_end_migration(struct mem_cgroup *mem,
         cgroup_release_and_wakeup_rmdir(&mem->css);
 }
 
-/*
- * A call to try to shrink memory usage on charge failure at shmem's swapin.
- * Calling hierarchical_reclaim is not enough because we should update
- * last_oom_jiffies to prevent pagefault_out_of_memory from invoking global OOM.
- * Moreover considering hierarchy, we should reclaim from the mem_over_limit,
- * not from the memcg which this page would be charged to.
- * try_charge_swapin does all of these works properly.
- */
-int mem_cgroup_shmem_charge_fallback(struct page *page,
-                            struct mm_struct *mm,
-                            gfp_t gfp_mask)
-{
-        struct mem_cgroup *mem;
-        int ret;
-
-        if (mem_cgroup_disabled())
-                return 0;
-
-        ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &mem);
-        if (!ret)
-                mem_cgroup_cancel_charge_swapin(mem); /* it does !mem check */
-
-        return ret;
-}
-
 #ifdef CONFIG_DEBUG_VM
 static struct page_cgroup *lookup_page_cgroup_used(struct page *page)
 {
@@ -5330,15 +5280,17 @@ static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
                 pgoff = pte_to_pgoff(ptent);
 
         /* page is moved even if it's not RSS of this task(page-faulted). */
-        if (!mapping_cap_swap_backed(mapping)) { /* normal file */
-                page = find_get_page(mapping, pgoff);
-        } else { /* shmem/tmpfs file. we should take account of swap too. */
-                swp_entry_t ent;
-                mem_cgroup_get_shmem_target(inode, pgoff, &page, &ent);
+        page = find_get_page(mapping, pgoff);
+
+#ifdef CONFIG_SWAP
+        /* shmem/tmpfs may report page out on swap: account for that too. */
+        if (radix_tree_exceptional_entry(page)) {
+                swp_entry_t swap = radix_to_swp_entry(page);
                 if (do_swap_account)
-                        entry->val = ent.val;
+                        *entry = swap;
+                page = find_get_page(&swapper_space, swap.val);
         }
-
+#endif
         return page;
 }