[RFC] [PATCH 2/9] memcg: atomic page_cgroup flags

KAMEZAWA Hiroyuki
2008-09-11T11:08:33Z

This patch makes page_cgroup->flags to be atomic_ops and define
functions (and macros) to access it.

This patch itself makes memcg slow but this patch's final purpose is
to remove lock_page_cgroup() (in some situation) and allowing fast
access (and no-dead-lock access) to page_cgroup.

Changelog: (v2) -> (v3)
- renamed macros and flags to be longer name.
- added comments.
- added "default bit set" for File, Shmem, Anon.

Changelog: (preview) -> (v1):
- patch ordering is changed.
- Added macro for defining functions for Test/Set/Clear bit.
- made the names of flags shorter.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

---
mm/memcontrol.c | 114 ++++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 82 insertions(+), 32 deletions(-)

Index: mmtom-2.6.27-rc5+/mm/memcontrol.c
===================================================================
--- mmtom-2.6.27-rc5+.orig/mm/memcontrol.c
+++ mmtom-2.6.27-rc5+/mm/memcontrol.c
@@ -161,12 +161,60 @@ struct page_cgroup {
struct list_head lru; /* per cgroup LRU list */
struct page *page;
struct mem_cgroup *mem_cgroup;
- int flags;
+ unsigned long flags;
};
-#define PAGE_CGROUP_FLAG_CACHE (0x1) /* charged as cache */
-#define PAGE_CGROUP_FLAG_ACTIVE (0x2) /* page is active in this cgroup */
-#define PAGE_CGROUP_FLAG_FILE (0x4) /* page is file system backed */
-#define PAGE_CGROUP_FLAG_UNEVICTABLE (0x8) /* page is unevictableable */
+
+enum {
+ /* flags for mem_cgroup */
+ PCG_CACHE, /* charged as cache */
+ /* flags for LRU placement */
+ PCG_ACTIVE, /* page is active in this cgroup */
+ PCG_FILE, /* page is file system backed */
+ PCG_UNEVICTABLE, /* page is unevictableable */
+};
+
+#define TESTPCGFLAG(uname, lname) \
+static inline int PageCgroup##uname(struct page_cgroup *pc) \
+ { return test_bit(PCG_##lname, &pc->flags); }
+
+#define SETPCGFLAG(uname, lname) \
+static inline void SetPageCgroup##uname(struct page_cgroup *pc)\
+ { set_bit(PCG_##lname, &pc->flags); }
+
+#define CLEARPCGFLAG(uname, lname) \
+static inline void ClearPageCgroup##uname(struct page_cgroup *pc) \
+ { clear_bit(PCG_##lname, &pc->flags); }
+
+#define __SETPCGFLAG(uname, lname) \
+static inline void __SetPageCgroup##uname(struct page_cgroup *pc)\
+ { __set_bit(PCG_##lname, &pc->flags); }
+
+#define __CLEARPCGFLAG(uname, lname) \
+static inline void __ClearPageCgroup##uname(struct page_cgroup *pc) \
+ { __clear_bit(PCG_##lname, &pc->flags); }
+
+/* Cache flag is set only once (at allocation) */
+TESTPCGFLAG(Cache, CACHE)
+__SETPCGFLAG(Cache, CACHE)
+
+/* LRU management flags (from global-lru definition) */
+TESTPCGFLAG(File, FILE)
+SETPCGFLAG(File, FILE)
+__SETPCGFLAG(File, FILE)
+CLEARPCGFLAG(File, FILE)
+
+TESTPCGFLAG(Active, ACTIVE)
+SETPCGFLAG(Active, ACTIVE)
+__SETPCGFLAG(Active, ACTIVE)
+CLEARPCGFLAG(Active, ACTIVE)
+
+TESTPCGFLAG(Unevictable, UNEVICTABLE)
+SETPCGFLAG(Unevictable, UNEVICTABLE)
+CLEARPCGFLAG(Unevictable, UNEVICTABLE)
+
+#define PcgDefaultAnonFlag ((1 << PCG_ACTIVE))
+#define PcgDefaultFileFlag ((1 << PCG_CACHE) | (1 << PCG_FILE))
+#define PcgDefaultShmemFlag ((1 << PCG_CACHE) | (1 << PCG_ACTIVE))

static int page_cgroup_nid(struct page_cgroup *pc)
{
@@ -187,14 +235,15 @@ enum charge_type {
/*
* Always modified under lru lock. Then, not necessary to preempt_disable()
*/
-static void mem_cgroup_charge_statistics(struct mem_cgroup *mem, int flags,
- bool charge)
+static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
+ struct page_cgroup *pc,
+ bool charge)
{
int val = (charge)? 1 : -1;
struct mem_cgroup_stat *stat = &mem->stat;

VM_BUG_ON(!irqs_disabled());
- if (flags & PAGE_CGROUP_FLAG_CACHE)
+ if (PageCgroupCache(pc))
__mem_cgroup_stat_add_safe(stat, MEM_CGROUP_STAT_CACHE, val);
else
__mem_cgroup_stat_add_safe(stat, MEM_CGROUP_STAT_RSS, val);
@@ -295,18 +344,18 @@ static void __mem_cgroup_remove_list(str
{
int lru = LRU_BASE;

- if (pc->flags & PAGE_CGROUP_FLAG_UNEVICTABLE)
+ if (PageCgroupUnevictable(pc))
lru = LRU_UNEVICTABLE;
else {
- if (pc->flags & PAGE_CGROUP_FLAG_ACTIVE)
+ if (PageCgroupActive(pc))
lru += LRU_ACTIVE;
- if (pc->flags & PAGE_CGROUP_FLAG_FILE)
+ if (PageCgroupFile(pc))
lru += LRU_FILE;
}

MEM_CGROUP_ZSTAT(mz, lru) -= 1;

- mem_cgroup_charge_statistics(pc->mem_cgroup, pc->flags, false);
+ mem_cgroup_charge_statistics(pc->mem_cgroup, pc, false);
list_del(&pc->lru);
}

@@ -315,27 +364,27 @@ static void __mem_cgroup_add_list(struct
{
int lru = LRU_BASE;

- if (pc->flags & PAGE_CGROUP_FLAG_UNEVICTABLE)
+ if (PageCgroupUnevictable(pc))
lru = LRU_UNEVICTABLE;
else {
- if (pc->flags & PAGE_CGROUP_FLAG_ACTIVE)
+ if (PageCgroupActive(pc))
lru += LRU_ACTIVE;
- if (pc->flags & PAGE_CGROUP_FLAG_FILE)
+ if (PageCgroupFile(pc))
lru += LRU_FILE;
}

MEM_CGROUP_ZSTAT(mz, lru) += 1;
list_add(&pc->lru, &mz->lists[lru]);

- mem_cgroup_charge_statistics(pc->mem_cgroup, pc->flags, true);
+ mem_cgroup_charge_statistics(pc->mem_cgroup, pc, true);
}

static void __mem_cgroup_move_lists(struct page_cgroup *pc, enum lru_list lru)
{
struct mem_cgroup_per_zone *mz = page_cgroup_zoneinfo(pc);
- int active = pc->flags & PAGE_CGROUP_FLAG_ACTIVE;
- int file = pc->flags & PAGE_CGROUP_FLAG_FILE;
- int unevictable = pc->flags & PAGE_CGROUP_FLAG_UNEVICTABLE;
+ int active = PageCgroupActive(pc);
+ int file = PageCgroupFile(pc);
+ int unevictable = PageCgroupUnevictable(pc);
enum lru_list from = unevictable ? LRU_UNEVICTABLE :
(LRU_FILE * !!file + !!active);

@@ -343,16 +392,20 @@ static void __mem_cgroup_move_lists(stru
return;

MEM_CGROUP_ZSTAT(mz, from) -= 1;
-
+ /*
+ * However this is done under mz->lru_lock, another flags, which
+ * are not related to LRU, will be modified from out-of-lock.
+ * We have to use atomic set/clear flags.
+ */
if (is_unevictable_lru(lru)) {
- pc->flags &= ~PAGE_CGROUP_FLAG_ACTIVE;
- pc->flags |= PAGE_CGROUP_FLAG_UNEVICTABLE;
+ ClearPageCgroupActive(pc);
+ SetPageCgroupUnevictable(pc);
} else {
if (is_active_lru(lru))
- pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
+ SetPageCgroupActive(pc);
else
- pc->flags &= ~PAGE_CGROUP_FLAG_ACTIVE;
- pc->flags &= ~PAGE_CGROUP_FLAG_UNEVICTABLE;
+ ClearPageCgroupActive(pc);
+ ClearPageCgroupUnevictable(pc);
}

MEM_CGROUP_ZSTAT(mz, lru) += 1;
@@ -585,18 +638,20 @@ static int mem_cgroup_charge_common(stru

pc->mem_cgroup = mem;
pc->page = page;
- /*
- * If a page is accounted as a page cache, insert to inactive list.
- * If anon, insert to active list.
- */
- if (ctype == MEM_CGROUP_CHARGE_TYPE_CACHE) {
- pc->flags = PAGE_CGROUP_FLAG_CACHE;
+
+ switch (ctype) {
+ case MEM_CGROUP_CHARGE_TYPE_CACHE:
if (page_is_file_cache(page))
- pc->flags |= PAGE_CGROUP_FLAG_FILE;
+ pc->flags = PcgDefaultFileFlag;
else
- pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
- } else
- pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
+ pc->flags = PcgDefaultShmemFlag;
+ break;
+ case MEM_CGROUP_CHARGE_TYPE_MAPPED:
+ pc->flags = PcgDefaultAnonFlag;
+ break;
+ default:
+ BUG();
+ }

lock_page_cgroup(page);
if (unlikely(page_get_page_cgroup(page))) {
@@ -704,8 +759,7 @@ __mem_cgroup_uncharge_common(struct page
VM_BUG_ON(pc->page != page);

if ((ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
- && ((pc->flags & PAGE_CGROUP_FLAG_CACHE)
- || page_mapped(page)))
+ && ((PageCgroupCache(pc) || page_mapped(page))))
goto unlock;

mz = page_cgroup_zoneinfo(pc);
@@ -755,7 +809,7 @@ int mem_cgroup_prepare_migration(struct
if (pc) {
mem = pc->mem_cgroup;
css_get(&mem->css);
- if (pc->flags & PAGE_CGROUP_FLAG_CACHE)
+ if (PageCgroupCache(pc))
ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
}
unlock_page_cgroup(page);