just for a RFC.

When I use memory controller, I notice that memory.limit_in_bytes shows
just very big number, if unlimited.

A user(or tool) has to know that the big number(LLONG_MAX) means "unlimted".
IMHO, some interface which allows users to specify "unlimited" value is helpful.

This patch tries to define value RES_COUTNER_UNLIMITED (== LLONG_MAX) and
modifies an interface to support "unlimted" value.

Because this patch breaks limit_in_bytes to some extent,
I'm glad if someone has a better idea to show unlimited value.
(if some easy value means "unlimited", it's helpful. LLONG_MAX is not easy
 to be recognized.)

==after this patch ==
[root@aworks kamezawa]# echo -n 400000000 > /opt/cgroup/memory.limit_in_bytes
[root@aworks kamezawa]# cat /opt/cgroup/memory.limit_in_bytes
400003072
[root@aworks kamezawa]# echo -n unlimited > /opt/cgroup/memory.limit_in_bytes
[root@aworks kamezawa]# cat /opt/cgroup/memory.limit_in_bytes
unlimited


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


 include/linux/res_counter.h |    1 +
 kernel/res_counter.c        |   11 ++++++++---
 2 files changed, 9 insertions(+), 3 deletions(-)

Index: linux-2.6.23-rc8-mm1/include/linux/res_counter.h
===================================================================
--- linux-2.6.23-rc8-mm1.orig/include/linux/res_counter.h
+++ linux-2.6.23-rc8-mm1/include/linux/res_counter.h
@@ -28,6 +28,7 @@ struct res_counter {
 	 * the limit that usage cannot exceed
 	 */
 	unsigned long long limit;
+#define RES_COUNTER_UNLIMITED		((unsigned long long)LLONG_MAX)
 	/*
 	 * the number of unsuccessful attempts to consume the resource
 	 */
Index: linux-2.6.23-rc8-mm1/kernel/res_counter.c
===================================================================
--- linux-2.6.23-rc8-mm1.orig/kernel/res_counter.c
+++ linux-2.6.23-rc8-mm1/kernel/res_counter.c
@@ -16,7 +16,7 @@
 void res_counter_init(struct res_counter *counter)
 {
 	spin_lock_init(&counter->lock);
-	counter->limit = (unsigned long long)LLONG_MAX;
+	counter->limit = RES_COUNTER_UNLIMITED;
 }
 
 int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
@@ -84,7 +84,9 @@ ssize_t res_counter_read(struct res_coun
 
 	s = buf;
 	val = res_counter_member(counter, member);
-	if (read_strategy)
+	if (*val == RES_COUNTER_UNLIMITED) {
+		s += sprintf(s, "unlimited\n", *val);
+	} else if (read_strategy)
 		s += read_strategy(*val, s);
 	else
 		s += sprintf(s, "%llu\n", *val);
@@ -112,7 +114,10 @@ ssize_t res_counter_write(struct res_cou
 
 	ret = -EINVAL;
 
-	if (write_strategy) {
+	if ((strcmp(buf, "-1") == 0) ||
+	    (strcmp(buf,"unlimited") == 0)) {
+		tmp = RES_COUNTER_UNLIMITED;
+	} else if(write_strategy) {
 		if (write_strategy(buf, &tmp)) {
 			goto out_free;
 		}

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