memcg: handle swap caches

SwapCache support for memory resource controller (memcg)

Before mem+swap controller, memcg itself should handle SwapCache in proper
way.  This is cut-out from it.

In current memcg, SwapCache is just leaked and the user can create tons of
SwapCache.  This is a leak of account and should be handled.

SwapCache accounting is done as following.

  charge (anon)
	- charged when it's mapped.
	  (because of readahead, charge at add_to_swap_cache() is not sane)
  uncharge (anon)
	- uncharged when it's dropped from swapcache and fully unmapped.
	  means it's not uncharged at unmap.
	  Note: delete from swap cache at swap-in is done after rmap information
	        is established.
  charge (shmem)
	- charged at swap-in. this prevents charge at add_to_page_cache().

  uncharge (shmem)
	- uncharged when it's dropped from swapcache and not on shmem's
	  radix-tree.

  at migration, check against 'old page' is modified to handle shmem.

Comparing to the old version discussed (and caused troubles), we have
advantages of
  - PCG_USED bit.
  - simple migrating handling.

So, situation is much easier than several months ago, maybe.

[hugh@veritas.com: memcg: handle swap caches build fix]
Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 2 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index bd9b4ea307b2..adf5c3eedbc9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -928,8 +928,12 @@ found:
         error = 1;
         if (!inode)
                 goto out;
-        /* Charge page using GFP_HIGHUSER_MOVABLE while we can wait */
-        error = mem_cgroup_cache_charge(page, current->mm, GFP_HIGHUSER_MOVABLE);
+        /*
+         * Charge page using GFP_HIGHUSER_MOVABLE while we can wait.
+         * charged back to the user(not to caller) when swap account is used.
+         */
+        error = mem_cgroup_cache_charge_swapin(page,
+                        current->mm, GFP_HIGHUSER_MOVABLE, true);
         if (error)
                 goto out;
         error = radix_tree_preload(GFP_KERNEL);
@@ -1266,6 +1270,16 @@ repeat:
                                 goto repeat;
                         }
                         wait_on_page_locked(swappage);
+                        /*
+                         * We want to avoid charge at add_to_page_cache().
+                         * charge against this swap cache here.
+                         */
+                        if (mem_cgroup_cache_charge_swapin(swappage,
+                                                current->mm, gfp, false)) {
+                                page_cache_release(swappage);
+                                error = -ENOMEM;
+                                goto failed;
+                        }
                         page_cache_release(swappage);
                         goto repeat;
                 }