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Message-ID: <20090517041543.GA5156@balbir.in.ibm.com>
Date: Sun, 17 May 2009 12:15:43 +0800
From: Balbir Singh <balbir@...ux.vnet.ibm.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
"menage@...gle.com" <menage@...gle.com>,
KOSAKI Motohiro <m-kosaki@...es.dti.ne.jp>
Subject: Re: [RFC] Low overhead patches for the memory cgroup controller
(v2)
* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-05-16 02:45:03]:
> I think set/clear flag here adds race condtion....because pc->flags is
> modfied by
> pc->flags = pcg_dafault_flags[ctype] in commit_charge()
> you have to modify above lines to be
>
> SetPageCgroupCache(pc) or some..
> ...
> SetPageCgroupUsed(pc)
>
> Then, you can use set_bit() without lock_page_cgroup().
> (Currently, pc->flags is modified only under lock_page_cgroup(), so,
> non atomic code is used.)
>
Here is the next version of the patch
Feature: Remove the overhead associated with the root cgroup
From: Balbir Singh <balbir@...ux.vnet.ibm.com>
This patch changes the memory cgroup and removes the overhead associated
with accounting all pages in the root cgroup. As a side-effect, we can
no longer set a memory hard limit in the root cgroup.
A new flag is used to track page_cgroup associated with the root cgroup
pages. A new flag to track whether the page has been accounted or not
has been added as well. Flags are now set atomically for page_cgroup,
pcg_default_flags is now obsolete, but I've not removed it yet. It
provides some readability to help the code.
Tests:
1. Tested lightly, previous versions showed good performance improvement 10%.
NOTE:
I haven't got the time right now to run oprofile and get detailed test results,
since I am in the middle of travel.
Please review the code for functional correctness and if you can test
it even better. I would like to push this in, especially if the %
performance difference I am seeing is reproducible elsewhere as well.
Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
---
include/linux/page_cgroup.h | 12 ++++++++++++
mm/memcontrol.c | 42 ++++++++++++++++++++++++++++++++++++++----
mm/page_cgroup.c | 1 -
3 files changed, 50 insertions(+), 5 deletions(-)
diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 7339c7b..ebdae9a 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -26,6 +26,8 @@ enum {
PCG_LOCK, /* page cgroup is locked */
PCG_CACHE, /* charged as cache */
PCG_USED, /* this object is in use. */
+ PCG_ROOT, /* page belongs to root cgroup */
+ PCG_ACCT, /* page has been accounted for */
};
#define TESTPCGFLAG(uname, lname) \
@@ -42,9 +44,19 @@ static inline void ClearPageCgroup##uname(struct page_cgroup *pc) \
/* Cache flag is set only once (at allocation) */
TESTPCGFLAG(Cache, CACHE)
+SETPCGFLAG(Cache, CACHE)
TESTPCGFLAG(Used, USED)
CLEARPCGFLAG(Used, USED)
+SETPCGFLAG(Used, USED)
+
+SETPCGFLAG(Root, ROOT)
+CLEARPCGFLAG(Root, ROOT)
+TESTPCGFLAG(Root, ROOT)
+
+SETPCGFLAG(Acct, ACCT)
+CLEARPCGFLAG(Acct, ACCT)
+TESTPCGFLAG(Acct, ACCT)
static inline int page_cgroup_nid(struct page_cgroup *pc)
{
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9712ef7..35415fc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -43,6 +43,7 @@
struct cgroup_subsys mem_cgroup_subsys __read_mostly;
#define MEM_CGROUP_RECLAIM_RETRIES 5
+struct mem_cgroup *root_mem_cgroup __read_mostly;
#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
/* Turned on only when memory cgroup is enabled && really_do_swap_account = 0 */
@@ -196,6 +197,10 @@ enum charge_type {
#define PCGF_CACHE (1UL << PCG_CACHE)
#define PCGF_USED (1UL << PCG_USED)
#define PCGF_LOCK (1UL << PCG_LOCK)
+/* Not used, but added here for completeness */
+#define PCGF_ROOT (1UL << PCG_ROOT)
+#define PCGF_ACCT (1UL << PCG_ACCT)
+
static const unsigned long
pcg_default_flags[NR_CHARGE_TYPE] = {
PCGF_CACHE | PCGF_USED | PCGF_LOCK, /* File Cache */
@@ -420,7 +425,7 @@ void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
return;
pc = lookup_page_cgroup(page);
/* can happen while we handle swapcache. */
- if (list_empty(&pc->lru) || !pc->mem_cgroup)
+ if ((!PageCgroupAcct(pc) && list_empty(&pc->lru)) || !pc->mem_cgroup)
return;
/*
* We don't check PCG_USED bit. It's cleared when the "page" is finally
@@ -429,6 +434,9 @@ void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
mz = page_cgroup_zoneinfo(pc);
mem = pc->mem_cgroup;
MEM_CGROUP_ZSTAT(mz, lru) -= 1;
+ ClearPageCgroupAcct(pc);
+ if (PageCgroupRoot(pc))
+ return;
list_del_init(&pc->lru);
return;
}
@@ -452,8 +460,8 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
* For making pc->mem_cgroup visible, insert smp_rmb() here.
*/
smp_rmb();
- /* unused page is not rotated. */
- if (!PageCgroupUsed(pc))
+ /* unused or root page is not rotated. */
+ if (!PageCgroupUsed(pc) || PageCgroupRoot(pc))
return;
mz = page_cgroup_zoneinfo(pc);
list_move(&pc->lru, &mz->lists[lru]);
@@ -477,6 +485,9 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
mz = page_cgroup_zoneinfo(pc);
MEM_CGROUP_ZSTAT(mz, lru) += 1;
+ SetPageCgroupAcct(pc);
+ if (PageCgroupRoot(pc))
+ return;
list_add(&pc->lru, &mz->lists[lru]);
}
@@ -1114,9 +1125,24 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
css_put(&mem->css);
return;
}
+
pc->mem_cgroup = mem;
smp_wmb();
- pc->flags = pcg_default_flags[ctype];
+ switch (ctype) {
+ case MEM_CGROUP_CHARGE_TYPE_CACHE:
+ case MEM_CGROUP_CHARGE_TYPE_SHMEM:
+ SetPageCgroupCache(pc);
+ SetPageCgroupUsed(pc);
+ break;
+ case MEM_CGROUP_CHARGE_TYPE_MAPPED:
+ SetPageCgroupUsed(pc);
+ break;
+ default:
+ break;
+ }
+
+ if (mem == root_mem_cgroup)
+ SetPageCgroupRoot(pc);
mem_cgroup_charge_statistics(mem, pc, true);
@@ -1521,6 +1547,8 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
mem_cgroup_charge_statistics(mem, pc, false);
ClearPageCgroupUsed(pc);
+ if (mem == root_mem_cgroup)
+ ClearPageCgroupRoot(pc);
/*
* pc->mem_cgroup is not cleared here. It will be accessed when it's
* freed from LRU. This is safe because uncharged page is expected not
@@ -2038,6 +2066,10 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
name = MEMFILE_ATTR(cft->private);
switch (name) {
case RES_LIMIT:
+ if (memcg == root_mem_cgroup) { /* Can't set limit on root */
+ ret = -EINVAL;
+ break;
+ }
/* This function does all necessary parse...reuse it */
ret = res_counter_memparse_write_strategy(buffer, &val);
if (ret)
@@ -2504,6 +2536,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
if (cont->parent == NULL) {
enable_swap_cgroup();
parent = NULL;
+ root_mem_cgroup = mem;
} else {
parent = mem_cgroup_from_cont(cont->parent);
mem->use_hierarchy = parent->use_hierarchy;
@@ -2532,6 +2565,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
return &mem->css;
free_out:
__mem_cgroup_free(mem);
+ root_mem_cgroup = NULL;
return ERR_PTR(error);
}
diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index 09b73c5..6145ff6 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -276,7 +276,6 @@ void __meminit pgdat_page_cgroup_init(struct pglist_data *pgdat)
#endif
-
#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
static DEFINE_MUTEX(swap_cgroup_mutex);
--
Balbir
--
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