mm: memcontrol: uncharge pages on swapout

This series gets rid of the remaining page_cgroup flags, thus cutting the
memcg per-page overhead down to one pointer.

This patch (of 4):

mem_cgroup_swapout() is called with exclusive access to the page at the
end of the page's lifetime.  Instead of clearing the PCG_MEMSW flag and
deferring the uncharge, just do it right away.  This allows follow-up
patches to simplify the uncharge code.

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

1 files changed, 14 insertions, 4 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8c10d4ca9c3f..266a440c89f9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5777,6 +5777,7 @@ static void __init enable_swap_cgroup(void)
  */
 void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 {
+        struct mem_cgroup *memcg;
         struct page_cgroup *pc;
         unsigned short oldid;
 
@@ -5793,13 +5794,22 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
                 return;
 
         VM_BUG_ON_PAGE(!(pc->flags & PCG_MEMSW), page);
+        memcg = pc->mem_cgroup;
 
-        oldid = swap_cgroup_record(entry, mem_cgroup_id(pc->mem_cgroup));
+        oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
         VM_BUG_ON_PAGE(oldid, page);
+        mem_cgroup_swap_statistics(memcg, true);
+
+        pc->flags = 0;
 
-        pc->flags &= ~PCG_MEMSW;
-        css_get(&pc->mem_cgroup->css);
-        mem_cgroup_swap_statistics(pc->mem_cgroup, true);
+        if (!mem_cgroup_is_root(memcg))
+                page_counter_uncharge(&memcg->memory, 1);
+
+        /* XXX: caller holds IRQ-safe mapping->tree_lock */
+        VM_BUG_ON(!irqs_disabled());
+
+        mem_cgroup_charge_statistics(memcg, page, -1);
+        memcg_check_events(memcg, page);
 }
 
 /**