aboutsummaryrefslogtreecommitdiff
path: root/mm/memcontrol.c
diff options
context:
space:
mode:
authorKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>2010-08-10 18:03:02 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-08-11 08:59:19 -0700
commitf75ca962037ffd639a44fd88933cd9b84c4c4411 (patch)
tree4773cd57ae45831c11783cd355f9dcb516eb66f0 /mm/memcontrol.c
parent158e0a2d1b3cffed8b46cbc56393a1394672ef79 (diff)
downloadvexpress-lsk-f75ca962037ffd639a44fd88933cd9b84c4c4411.tar.gz
memcg: avoid css_get()
Now, memory cgroup increments css(cgroup subsys state)'s reference count per a charged page. And the reference count is kept until the page is uncharged. But this has 2 bad effect. 1. Because css_get/put calls atomic_inc()/dec, heavy call of them on large smp will not scale well. 2. Because css's refcnt cannot be in a state as "ready-to-release", cgroup's notify_on_release handler can't work with memcg. 3. css's refcnt is atomic_t, it means smaller than 32bit. Maybe too small. This has been a problem since the 1st merge of memcg. This is a trial to remove css's refcnt per a page. Even if we remove refcnt, pre_destroy() does enough synchronization as - check res->usage == 0. - check no pages on LRU. This patch removes css's refcnt per page. Even after this patch, at the 1st look, it seems css_get() is still called in try_charge(). But the logic is. - If a memcg of mm->owner is cached one, consume_stock() will work. At success, return immediately. - If consume_stock returns false, css_get() is called and go to slow path which may be blocked. At the end of slow path, css_put() is called and restart from the start if necessary. So, in the fast path, we don't call css_get() and can avoid access to shared counter. This patch can make the most possible case fast. Here is a result of multi-threaded page fault benchmark. [Before] 25.32% multi-fault-all [kernel.kallsyms] [k] clear_page_c 9.30% multi-fault-all [kernel.kallsyms] [k] _raw_spin_lock_irqsave 8.02% multi-fault-all [kernel.kallsyms] [k] try_get_mem_cgroup_from_mm <=====(*) 7.83% multi-fault-all [kernel.kallsyms] [k] down_read_trylock 5.38% multi-fault-all [kernel.kallsyms] [k] __css_put 5.29% multi-fault-all [kernel.kallsyms] [k] __alloc_pages_nodemask 4.92% multi-fault-all [kernel.kallsyms] [k] _raw_spin_lock_irq 4.24% multi-fault-all [kernel.kallsyms] [k] up_read 3.53% multi-fault-all [kernel.kallsyms] [k] css_put 2.11% multi-fault-all [kernel.kallsyms] [k] handle_mm_fault 1.76% multi-fault-all [kernel.kallsyms] [k] __rmqueue 1.64% multi-fault-all [kernel.kallsyms] [k] __mem_cgroup_commit_charge [After] 28.41% multi-fault-all [kernel.kallsyms] [k] clear_page_c 10.08% multi-fault-all [kernel.kallsyms] [k] _raw_spin_lock_irq 9.58% multi-fault-all [kernel.kallsyms] [k] down_read_trylock 9.38% multi-fault-all [kernel.kallsyms] [k] _raw_spin_lock_irqsave 5.86% multi-fault-all [kernel.kallsyms] [k] __alloc_pages_nodemask 5.65% multi-fault-all [kernel.kallsyms] [k] up_read 2.82% multi-fault-all [kernel.kallsyms] [k] handle_mm_fault 2.64% multi-fault-all [kernel.kallsyms] [k] mem_cgroup_add_lru_list 2.48% multi-fault-all [kernel.kallsyms] [k] __mem_cgroup_commit_charge Then, 8.02% of try_get_mem_cgroup_from_mm() disappears because this patch removes css_tryget() in it. (But yes, this is an extreme case.) Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Cc: Balbir Singh <balbir@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memcontrol.c')
-rw-r--r--mm/memcontrol.c119
1 files changed, 76 insertions, 43 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f52b0a1861c..a1c3c317a4d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1714,28 +1714,66 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
* thread group leader migrates. It's possible that mm is not
* set, if so charge the init_mm (happens for pagecache usage).
*/
- if (*memcg) {
+ if (!*memcg && !mm)
+ goto bypass;
+again:
+ if (*memcg) { /* css should be a valid one */
mem = *memcg;
+ VM_BUG_ON(css_is_removed(&mem->css));
+ if (mem_cgroup_is_root(mem))
+ goto done;
+ if (consume_stock(mem))
+ goto done;
css_get(&mem->css);
} else {
- mem = try_get_mem_cgroup_from_mm(mm);
- if (unlikely(!mem))
- return 0;
- *memcg = mem;
- }
+ struct task_struct *p;
- VM_BUG_ON(css_is_removed(&mem->css));
- if (mem_cgroup_is_root(mem))
- goto done;
+ rcu_read_lock();
+ p = rcu_dereference(mm->owner);
+ VM_BUG_ON(!p);
+ /*
+ * because we don't have task_lock(), "p" can exit while
+ * we're here. In that case, "mem" can point to root
+ * cgroup but never be NULL. (and task_struct itself is freed
+ * by RCU, cgroup itself is RCU safe.) Then, we have small
+ * risk here to get wrong cgroup. But such kind of mis-account
+ * by race always happens because we don't have cgroup_mutex().
+ * It's overkill and we allow that small race, here.
+ */
+ mem = mem_cgroup_from_task(p);
+ VM_BUG_ON(!mem);
+ if (mem_cgroup_is_root(mem)) {
+ rcu_read_unlock();
+ goto done;
+ }
+ if (consume_stock(mem)) {
+ /*
+ * It seems dagerous to access memcg without css_get().
+ * But considering how consume_stok works, it's not
+ * necessary. If consume_stock success, some charges
+ * from this memcg are cached on this cpu. So, we
+ * don't need to call css_get()/css_tryget() before
+ * calling consume_stock().
+ */
+ rcu_read_unlock();
+ goto done;
+ }
+ /* after here, we may be blocked. we need to get refcnt */
+ if (!css_tryget(&mem->css)) {
+ rcu_read_unlock();
+ goto again;
+ }
+ rcu_read_unlock();
+ }
do {
bool oom_check;
- if (consume_stock(mem))
- goto done; /* don't need to fill stock */
/* If killed, bypass charge */
- if (fatal_signal_pending(current))
+ if (fatal_signal_pending(current)) {
+ css_put(&mem->css);
goto bypass;
+ }
oom_check = false;
if (oom && !nr_oom_retries) {
@@ -1750,30 +1788,36 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
break;
case CHARGE_RETRY: /* not in OOM situation but retry */
csize = PAGE_SIZE;
- break;
+ css_put(&mem->css);
+ mem = NULL;
+ goto again;
case CHARGE_WOULDBLOCK: /* !__GFP_WAIT */
+ css_put(&mem->css);
goto nomem;
case CHARGE_NOMEM: /* OOM routine works */
- if (!oom)
+ if (!oom) {
+ css_put(&mem->css);
goto nomem;
+ }
/* If oom, we never return -ENOMEM */
nr_oom_retries--;
break;
case CHARGE_OOM_DIE: /* Killed by OOM Killer */
+ css_put(&mem->css);
goto bypass;
}
} while (ret != CHARGE_OK);
if (csize > PAGE_SIZE)
refill_stock(mem, csize - PAGE_SIZE);
+ css_put(&mem->css);
done:
+ *memcg = mem;
return 0;
nomem:
- css_put(&mem->css);
+ *memcg = NULL;
return -ENOMEM;
bypass:
- if (mem)
- css_put(&mem->css);
*memcg = NULL;
return 0;
}
@@ -1790,11 +1834,7 @@ static void __mem_cgroup_cancel_charge(struct mem_cgroup *mem,
res_counter_uncharge(&mem->res, PAGE_SIZE * count);
if (do_swap_account)
res_counter_uncharge(&mem->memsw, PAGE_SIZE * count);
- VM_BUG_ON(test_bit(CSS_ROOT, &mem->css.flags));
- WARN_ON_ONCE(count > INT_MAX);
- __css_put(&mem->css, (int)count);
}
- /* we don't need css_put for root */
}
static void mem_cgroup_cancel_charge(struct mem_cgroup *mem)
@@ -2155,7 +2195,6 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
goto charge_cur_mm;
*ptr = mem;
ret = __mem_cgroup_try_charge(NULL, mask, ptr, true);
- /* drop extra refcnt from tryget */
css_put(&mem->css);
return ret;
charge_cur_mm:
@@ -2325,10 +2364,6 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
break;
}
- if (!mem_cgroup_is_root(mem))
- __do_uncharge(mem, ctype);
- if (ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
- mem_cgroup_swap_statistics(mem, true);
mem_cgroup_charge_statistics(mem, pc, false);
ClearPageCgroupUsed(pc);
@@ -2340,11 +2375,17 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
*/
unlock_page_cgroup(pc);
-
+ /*
+ * even after unlock, we have mem->res.usage here and this memcg
+ * will never be freed.
+ */
memcg_check_events(mem, page);
- /* at swapout, this memcg will be accessed to record to swap */
- if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
- css_put(&mem->css);
+ if (do_swap_account && ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT) {
+ mem_cgroup_swap_statistics(mem, true);
+ mem_cgroup_get(mem);
+ }
+ if (!mem_cgroup_is_root(mem))
+ __do_uncharge(mem, ctype);
return mem;
@@ -2431,13 +2472,12 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
memcg = __mem_cgroup_uncharge_common(page, ctype);
- /* record memcg information */
- if (do_swap_account && swapout && memcg) {
+ /*
+ * record memcg information, if swapout && memcg != NULL,
+ * mem_cgroup_get() was called in uncharge().
+ */
+ if (do_swap_account && swapout && memcg)
swap_cgroup_record(ent, css_id(&memcg->css));
- mem_cgroup_get(memcg);
- }
- if (swapout && memcg)
- css_put(&memcg->css);
}
#endif
@@ -2515,7 +2555,6 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
*/
if (!mem_cgroup_is_root(to))
res_counter_uncharge(&to->res, PAGE_SIZE);
- css_put(&to->css);
}
return 0;
}
@@ -4214,9 +4253,6 @@ static int mem_cgroup_do_precharge(unsigned long count)
goto one_by_one;
}
mc.precharge += count;
- VM_BUG_ON(test_bit(CSS_ROOT, &mem->css.flags));
- WARN_ON_ONCE(count > INT_MAX);
- __css_get(&mem->css, (int)count);
return ret;
}
one_by_one:
@@ -4452,7 +4488,6 @@ static void mem_cgroup_clear_mc(void)
}
/* we must fixup refcnts and charges */
if (mc.moved_swap) {
- WARN_ON_ONCE(mc.moved_swap > INT_MAX);
/* uncharge swap account from the old cgroup */
if (!mem_cgroup_is_root(mc.from))
res_counter_uncharge(&mc.from->memsw,
@@ -4466,8 +4501,6 @@ static void mem_cgroup_clear_mc(void)
*/
res_counter_uncharge(&mc.to->res,
PAGE_SIZE * mc.moved_swap);
- VM_BUG_ON(test_bit(CSS_ROOT, &mc.to->css.flags));
- __css_put(&mc.to->css, mc.moved_swap);
}
/* we've already done mem_cgroup_get(mc.to) */