[RFC][PATCH 3/6] memcg: add PageCgroupReset()
From: KAMEZAWA Hiroyuki <hidden>
Date: 2012-03-28 10:59:05
Also in:
lkml
Subsystem:
control group - memory resource controller (memcg), memory management, the rest · Maintainers:
Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt, Andrew Morton, Linus Torvalds
A commit "memcg: simplify LRU handling by new rule" removes PCG_ACCT_LRU. and the bug introduced by it was fixed by "memcg: fix GPF when cgroup removal races with last exit" This was for reducing flags on pc->flags....Now, we have 3bits of flags. but this patch adds a new flag, I'm sorry. (Considering alignment of kmalloc(), we'll able to have 5 bits..) This patch adds PCG_RESET which is similar to PCG_ACCT_LRU. This is set when mem_cgroup_add_lru_list() finds we cannot trust the pc's mem_cgroup. The reason why this patch adds a (renamed) flag again is for merging pc->flags and pc->mem_cgroup. Assume pc's mem_cgroup is encoded as mem_cgroup = pc->flags & ~0x7 Updating multiple bits of pc->flags without talking lock_page_cgroup() is very dangerous. And mem_cgroup_add_lru_list() updates pc->mem_cgroup without taking lock. Then I add RESET bit. After this, pc_to_mem_cgroup() is written as if (PageCgroupReset(pc)) return root_mem_cgroup; return pc->mem_cgroup; This update of Reset bit can be done in atomic by set_bit(). And cleared when USED bit is set. Considering kmalloc()'s alignment, having 4bits of flags will be ok.... Signed-off-by: KAMEZAWA Hiroyuki <redacted> --- include/linux/page_cgroup.h | 15 ++++++++------- mm/memcontrol.c | 5 +++-- 2 files changed, 11 insertions(+), 9 deletions(-)
diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 2707809..3f3b4ff 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h@@ -8,6 +8,7 @@ enum { PCG_LOCK, /* Lock for pc->mem_cgroup and following bits. */ PCG_USED, /* this object is in use. */ PCG_MIGRATION, /* under page migration */ + PCG_RESET, /* have been reset to root_mem_cgroup */ __NR_PCG_FLAGS, };
@@ -70,6 +71,9 @@ SETPCGFLAG(Migration, MIGRATION) CLEARPCGFLAG(Migration, MIGRATION) TESTPCGFLAG(Migration, MIGRATION) +TESTPCGFLAG(Reset, RESET) +SETPCGFLAG(Reset, RESET) + static inline void lock_page_cgroup(struct page_cgroup *pc) { /*
@@ -84,16 +88,13 @@ static inline void unlock_page_cgroup(struct page_cgroup *pc) bit_spin_unlock(PCG_LOCK, &pc->flags); } +extern struct mem_cgroup* root_mem_cgroup; static inline struct mem_cgroup* pc_to_mem_cgroup(struct page_cgroup *pc) { - return pc->mem_cgroup; -} - -static inline void -pc_set_mem_cgroup(struct page_cgroup *pc, struct mem_cgroup *memcg) -{ - pc->mem_cgroup = memcg; + if (likely(!PageCgroupReset(pc))) + return pc->mem_cgroup; + return root_mem_cgroup; } static inline void
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d366b60..622fd2e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c@@ -1080,7 +1080,8 @@ struct lruvec *mem_cgroup_lru_add_list(struct zone *zone, struct page *page, * of pc's mem_cgroup safe. */ if (!PageCgroupUsed(pc) && memcg != root_mem_cgroup) { - pc_set_mem_cgroup(pc, root_mem_cgroup); + /* this reset bit is cleared when the page is charged */ + SetPageCgroupReset(pc); memcg = root_mem_cgroup; }
@@ -2626,7 +2627,7 @@ static int mem_cgroup_move_account(struct page *page, __mem_cgroup_cancel_charge(from, nr_pages); /* caller should have done css_get */ - pc_set_mem_cgroup(pc, to); + pc_set_mem_cgroup_and_flags(pc, to, BIT(PCG_USED) | BIT(PCG_LOCK)); mem_cgroup_charge_statistics(to, anon, nr_pages); /* * We charges against "to" which may not have any tasks. Then, "to"
--
1.7.4.1
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