memcg: remove direct page_cgroup-to-page pointer

In struct page_cgroup, we have a full word for flags but only a few are
reserved.  Use the remaining upper bits to encode, depending on
configuration, the node or the section, to enable page_cgroup-to-page
lookups without a direct pointer.

This saves a full word for every page in a system with memory cgroups
enabled.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 58 insertions, 17 deletions

diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 6b63679ce8a1..f5de21de31dd 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -1,8 +1,26 @@
 #ifndef __LINUX_PAGE_CGROUP_H
 #define __LINUX_PAGE_CGROUP_H
 
+enum {
+        /* flags for mem_cgroup */
+        PCG_LOCK,  /* Lock for pc->mem_cgroup and following bits. */
+        PCG_CACHE, /* charged as cache */
+        PCG_USED, /* this object is in use. */
+        PCG_MIGRATION, /* under page migration */
+        /* flags for mem_cgroup and file and I/O status */
+        PCG_MOVE_LOCK, /* For race between move_account v.s. following bits */
+        PCG_FILE_MAPPED, /* page is accounted as "mapped" */
+        /* No lock in page_cgroup */
+        PCG_ACCT_LRU, /* page has been accounted for (under lru_lock) */
+        __NR_PCG_FLAGS,
+};
+
+#ifndef __GENERATING_BOUNDS_H
+#include <generated/bounds.h>
+
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
 #include <linux/bit_spinlock.h>
+
 /*
  * Page Cgroup can be considered as an extended mem_map.
  * A page_cgroup page is associated with every page descriptor. The
@@ -13,7 +31,6 @@
 struct page_cgroup {
         unsigned long flags;
         struct mem_cgroup *mem_cgroup;
-        struct page *page;
         struct list_head lru;           /* per cgroup LRU list */
 };
 
@@ -32,19 +49,7 @@ static inline void __init page_cgroup_init(void)
 #endif
 
 struct page_cgroup *lookup_page_cgroup(struct page *page);
-
-enum {
-        /* flags for mem_cgroup */
-        PCG_LOCK,  /* Lock for pc->mem_cgroup and following bits. */
-        PCG_CACHE, /* charged as cache */
-        PCG_USED, /* this object is in use. */
-        PCG_MIGRATION, /* under page migration */
-        /* flags for mem_cgroup and file and I/O status */
-        PCG_MOVE_LOCK, /* For race between move_account v.s. following bits */
-        PCG_FILE_MAPPED, /* page is accounted as "mapped" */
-        /* No lock in page_cgroup */
-        PCG_ACCT_LRU, /* page has been accounted for (under lru_lock) */
-};
+struct page *lookup_cgroup_page(struct page_cgroup *pc);
 
 #define TESTPCGFLAG(uname, lname)                       \
 static inline int PageCgroup##uname(struct page_cgroup *pc)     \
@@ -117,6 +122,39 @@ static inline void move_unlock_page_cgroup(struct page_cgroup *pc,
         local_irq_restore(*flags);
 }
 
+#ifdef CONFIG_SPARSEMEM
+#define PCG_ARRAYID_WIDTH       SECTIONS_SHIFT
+#else
+#define PCG_ARRAYID_WIDTH       NODES_SHIFT
+#endif
+
+#if (PCG_ARRAYID_WIDTH > BITS_PER_LONG - NR_PCG_FLAGS)
+#error Not enough space left in pc->flags to store page_cgroup array IDs
+#endif
+
+/* pc->flags: ARRAY-ID | FLAGS */
+
+#define PCG_ARRAYID_MASK        ((1UL << PCG_ARRAYID_WIDTH) - 1)
+
+#define PCG_ARRAYID_OFFSET      (BITS_PER_LONG - PCG_ARRAYID_WIDTH)
+/*
+ * Zero the shift count for non-existant fields, to prevent compiler
+ * warnings and ensure references are optimized away.
+ */
+#define PCG_ARRAYID_SHIFT       (PCG_ARRAYID_OFFSET * (PCG_ARRAYID_WIDTH != 0))
+
+static inline void set_page_cgroup_array_id(struct page_cgroup *pc,
+                                            unsigned long id)
+{
+        pc->flags &= ~(PCG_ARRAYID_MASK << PCG_ARRAYID_SHIFT);
+        pc->flags |= (id & PCG_ARRAYID_MASK) << PCG_ARRAYID_SHIFT;
+}
+
+static inline unsigned long page_cgroup_array_id(struct page_cgroup *pc)
+{
+        return (pc->flags >> PCG_ARRAYID_SHIFT) & PCG_ARRAYID_MASK;
+}
+
 #else /* CONFIG_CGROUP_MEM_RES_CTLR */
 struct page_cgroup;
 
@@ -137,7 +175,7 @@ static inline void __init page_cgroup_init_flatmem(void)
 {
 }
 
-#endif
+#endif /* CONFIG_CGROUP_MEM_RES_CTLR */
 
 #include <linux/swap.h>
 
@@ -173,5 +211,8 @@ static inline void swap_cgroup_swapoff(int type)
         return;
 }
 
-#endif
-#endif
+#endif /* CONFIG_CGROUP_MEM_RES_CTLR_SWAP */
+
+#endif /* !__GENERATING_BOUNDS_H */
+
+#endif /* __LINUX_PAGE_CGROUP_H */