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Subject[patch 5/5] memcg: remove direct page_cgroup-to-page pointer
Date
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>
---
include/linux/page_cgroup.h | 70 +++++++++++++++++++++++++++---------
kernel/bounds.c | 2 +
mm/memcontrol.c | 6 ++-
mm/page_cgroup.c | 85 +++++++++++++++++++++++++------------------
4 files changed, 108 insertions(+), 55 deletions(-)
diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 6b63679..05d8618 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 +122,34 @@ static inline void move_unlock_page_cgroup(struct page_cgroup *pc,
local_irq_restore(*flags);
}

+#ifdef CONFIG_SPARSEMEM
+#define PCG_ARRAYID_SHIFT SECTIONS_SHIFT
+#else
+#define PCG_ARRAYID_SHIFT NODES_SHIFT
+#endif
+
+#if (PCG_ARRAYID_SHIFT > 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_SHIFT) - 1)
+
+#define PCG_ARRAYID_OFFSET (sizeof(unsigned long) * 8 - PCG_ARRAYID_SHIFT)
+
+static inline void set_page_cgroup_array_id(struct page_cgroup *pc,
+ unsigned long id)
+{
+ pc->flags &= ~(PCG_ARRAYID_MASK << PCG_ARRAYID_OFFSET);
+ pc->flags |= (id & PCG_ARRAYID_MASK) << PCG_ARRAYID_OFFSET;
+}
+
+static inline unsigned long page_cgroup_array_id(struct page_cgroup *pc)
+{
+ return (pc->flags >> PCG_ARRAYID_OFFSET) & PCG_ARRAYID_MASK;
+}
+
#else /* CONFIG_CGROUP_MEM_RES_CTLR */
struct page_cgroup;

@@ -137,7 +170,7 @@ static inline void __init page_cgroup_init_flatmem(void)
{
}

-#endif
+#endif /* CONFIG_CGROUP_MEM_RES_CTLR */

#include <linux/swap.h>

@@ -173,5 +206,8 @@ 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 */
diff --git a/kernel/bounds.c b/kernel/bounds.c
index 98a51f2..0c9b862 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -9,11 +9,13 @@
#include <linux/page-flags.h>
#include <linux/mmzone.h>
#include <linux/kbuild.h>
+#include <linux/page_cgroup.h>

void foo(void)
{
/* The enum constants to put into include/generated/bounds.h */
DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
+ DEFINE(NR_PCG_FLAGS, __NR_PCG_FLAGS);
/* End of constants */
}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 998da06..4e10f46 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1054,7 +1054,8 @@ unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
if (unlikely(!PageCgroupUsed(pc)))
continue;

- page = pc->page;
+ page = lookup_cgroup_page(pc);
+ VM_BUG_ON(pc != lookup_page_cgroup(page));

if (unlikely(!PageLRU(page)))
continue;
@@ -3296,7 +3297,8 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *mem,
}
spin_unlock_irqrestore(&zone->lru_lock, flags);

- page = pc->page;
+ page = lookup_cgroup_page(pc);
+ VM_BUG_ON(pc != lookup_page_cgroup(page));

ret = mem_cgroup_move_parent(page, pc, mem, GFP_KERNEL);
if (ret == -ENOMEM)
diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index 59a3cd4..e5f38e8 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -11,12 +11,11 @@
#include <linux/swapops.h>
#include <linux/kmemleak.h>

-static void __meminit
-__init_page_cgroup(struct page_cgroup *pc, unsigned long pfn)
+static void __meminit init_page_cgroup(struct page_cgroup *pc, unsigned long id)
{
pc->flags = 0;
+ set_page_cgroup_array_id(pc, id);
pc->mem_cgroup = NULL;
- pc->page = pfn_to_page(pfn);
INIT_LIST_HEAD(&pc->lru);
}
static unsigned long total_usage;
@@ -43,6 +42,16 @@ struct page_cgroup *lookup_page_cgroup(struct page *page)
return base + offset;
}

+struct page *lookup_cgroup_page(struct page_cgroup *pc)
+{
+ unsigned long pfn;
+ pg_data_t *pgdat;
+
+ pgdat = NODE_DATA(page_cgroup_array_id(pc));
+ pfn = pc - pgdat->node_page_cgroup + pgdat->node_start_pfn;
+ return pfn_to_page(pfn);
+}
+
static int __init alloc_node_page_cgroup(int nid)
{
struct page_cgroup *base, *pc;
@@ -63,7 +72,7 @@ static int __init alloc_node_page_cgroup(int nid)
return -ENOMEM;
for (index = 0; index < nr_pages; index++) {
pc = base + index;
- __init_page_cgroup(pc, start_pfn + index);
+ init_page_cgroup(pc, nid);
}
NODE_DATA(nid)->node_page_cgroup = base;
total_usage += table_size;
@@ -105,46 +114,50 @@ struct page_cgroup *lookup_page_cgroup(struct page *page)
return section->page_cgroup + pfn;
}

+struct page *lookup_cgroup_page(struct page_cgroup *pc)
+{
+ struct mem_section *section;
+ unsigned long nr;
+
+ nr = page_cgroup_array_id(pc);
+ section = __nr_to_section(nr);
+ return pfn_to_page(pc - section->page_cgroup);
+}
+
/* __alloc_bootmem...() is protected by !slab_available() */
static int __init_refok init_section_page_cgroup(unsigned long pfn)
{
- struct mem_section *section = __pfn_to_section(pfn);
struct page_cgroup *base, *pc;
+ struct mem_section *section;
unsigned long table_size;
+ unsigned long nr;
int nid, index;

- if (!section->page_cgroup) {
- nid = page_to_nid(pfn_to_page(pfn));
- table_size = sizeof(struct page_cgroup) * PAGES_PER_SECTION;
- VM_BUG_ON(!slab_is_available());
- if (node_state(nid, N_HIGH_MEMORY)) {
- base = kmalloc_node(table_size,
- GFP_KERNEL | __GFP_NOWARN, nid);
- if (!base)
- base = vmalloc_node(table_size, nid);
- } else {
- base = kmalloc(table_size, GFP_KERNEL | __GFP_NOWARN);
- if (!base)
- base = vmalloc(table_size);
- }
- /*
- * The value stored in section->page_cgroup is (base - pfn)
- * and it does not point to the memory block allocated above,
- * causing kmemleak false positives.
- */
- kmemleak_not_leak(base);
+ nr = pfn_to_section_nr(pfn);
+ section = __nr_to_section(nr);
+
+ if (section->page_cgroup)
+ return 0;
+
+ nid = page_to_nid(pfn_to_page(pfn));
+ table_size = sizeof(struct page_cgroup) * PAGES_PER_SECTION;
+ VM_BUG_ON(!slab_is_available());
+ if (node_state(nid, N_HIGH_MEMORY)) {
+ base = kmalloc_node(table_size,
+ GFP_KERNEL | __GFP_NOWARN, nid);
+ if (!base)
+ base = vmalloc_node(table_size, nid);
} else {
- /*
- * We don't have to allocate page_cgroup again, but
- * address of memmap may be changed. So, we have to initialize
- * again.
- */
- base = section->page_cgroup + pfn;
- table_size = 0;
- /* check address of memmap is changed or not. */
- if (base->page == pfn_to_page(pfn))
- return 0;
+ base = kmalloc(table_size, GFP_KERNEL | __GFP_NOWARN);
+ if (!base)
+ base = vmalloc(table_size);
}
+ /*
+ * The value stored in section->page_cgroup is (base - pfn)
+ * and it does not point to the memory block allocated above,
+ * causing kmemleak false positives.
+ */
+ kmemleak_not_leak(base);

if (!base) {
printk(KERN_ERR "page cgroup allocation failure\n");
@@ -153,7 +166,7 @@ static int __init_refok init_section_page_cgroup(unsigned long pfn)

for (index = 0; index < PAGES_PER_SECTION; index++) {
pc = base + index;
- __init_page_cgroup(pc, pfn + index);
+ init_page_cgroup(pc, nr);
}

section->page_cgroup = base - pfn;
--
1.7.4


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