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Subject[PATCH 1/6] res_counter: handle limit change
Add a support to shrink_usage_at_limit_change feature to res_counter.
memcg will use this to drop pages.

Change log: xxx -> v4 (new file.)
- cut out the limit-change part from hierarchy patch set.
- add "retry_count" arguments to shrink_usage(). This allows that we don't
have to set the default retry loop count.
- res_counter_check_under_val() is added to support subsystem.
- res_counter_init() is res_counter_init_ops(cnt, NULL)

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

---
Documentation/controllers/resource_counter.txt | 19 +++++-
include/linux/res_counter.h | 33 ++++++++++-
kernel/res_counter.c | 74 ++++++++++++++++++++++++-
3 files changed, 121 insertions(+), 5 deletions(-)

Index: linux-2.6.26-rc5-mm3/include/linux/res_counter.h
===================================================================
--- linux-2.6.26-rc5-mm3.orig/include/linux/res_counter.h
+++ linux-2.6.26-rc5-mm3/include/linux/res_counter.h
@@ -21,6 +21,13 @@
* the helpers described beyond
*/

+struct res_counter;
+struct res_counter_ops {
+ /* called when the subsystem has to reduce the usage. */
+ int (*shrink_usage)(struct res_counter *cnt, unsigned long long val,
+ int retry_count);
+};
+
struct res_counter {
/*
* the current resource consumption level
@@ -39,6 +46,10 @@ struct res_counter {
*/
unsigned long long failcnt;
/*
+ * registered callbacks etc...for res_counter.
+ */
+ struct res_counter_ops ops;
+ /*
* the lock to protect all of the above.
* the routines below consider this to be IRQ-safe
*/
@@ -82,7 +93,13 @@ enum {
* helpers for accounting
*/

-void res_counter_init(struct res_counter *counter);
+void res_counter_init_ops(struct res_counter *counter,
+ struct res_counter_ops *ops);
+
+static inline void res_counter_init(struct res_counter *counter)
+{
+ res_counter_init_ops(counter, NULL);
+}

/*
* charge - try to consume more resource.
@@ -136,6 +153,20 @@ static inline bool res_counter_check_und
return ret;
}

+static inline bool res_counter_check_under_val(struct res_counter *cnt,
+ unsigned long long val)
+{
+ bool ret = false;
+ unsigned long flags;
+
+ spin_lock_irqsave(&cnt->lock, flags);
+ if (cnt->usage <= val)
+ ret = true;
+ spin_unlock_irqrestore(&cnt->lock, flags);
+
+ return ret;
+}
+
static inline void res_counter_reset_max(struct res_counter *cnt)
{
unsigned long flags;
Index: linux-2.6.26-rc5-mm3/kernel/res_counter.c
===================================================================
--- linux-2.6.26-rc5-mm3.orig/kernel/res_counter.c
+++ linux-2.6.26-rc5-mm3/kernel/res_counter.c
@@ -14,10 +14,22 @@
#include <linux/res_counter.h>
#include <linux/uaccess.h>

-void res_counter_init(struct res_counter *counter)
+/**
+ * res_counter_init_ops -- initialize res_counter.
+ * @counter: the res_counter to be initialized
+ * @ops: the res_counter_ops for this res_counter. This argument can be NULL
+ * and is copied.
+ *
+ * init spinlock and set limit to be very very big value.
+ */
+
+void res_counter_init_ops(struct res_counter *counter,
+ struct res_counter_ops *ops)
{
spin_lock_init(&counter->lock);
counter->limit = (unsigned long long)LLONG_MAX;
+ if (ops)
+ counter->ops = *ops;
}

int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
@@ -102,6 +114,46 @@ u64 res_counter_read_u64(struct res_coun
return *res_counter_member(counter, member);
}

+/*
+ * Called when the limit changes if res_counter has ops->shrink_usage.
+ * This function uses shrink usage to below new limit. returns 0 at success.
+ */
+
+static int res_counter_resize_limit(struct res_counter *cnt,
+ unsigned long long val)
+{
+ int retry_count = 0;
+ int ret = -EBUSY;
+ unsigned long flags;
+
+ BUG_ON(!cnt->ops.shrink_usage);
+ while (1) {
+ spin_lock_irqsave(&cnt->lock, flags);
+ if (cnt->usage <= val) {
+ cnt->limit = val;
+ ret = 0;
+ spin_unlock_irqrestore(&cnt->lock, flags);
+ break;
+ }
+ BUG_ON(val > cnt->limit);
+ spin_unlock_irqrestore(&cnt->lock, flags);
+
+ /*
+ * Rest before calling callback().... rest after callback
+ * tends to add difference between the result of callback and
+ * the check in next loop.
+ */
+ cond_resched();
+
+ ret = cnt->ops.shrink_usage(cnt, val, retry_count);
+ if (!ret)
+ break;
+ retry_count++;
+ }
+ return ret;
+}
+
+
ssize_t res_counter_write(struct res_counter *counter, int member,
const char __user *userbuf, size_t nbytes, loff_t *pos,
int (*write_strategy)(char *st_buf, unsigned long long *val))
@@ -133,11 +185,29 @@ ssize_t res_counter_write(struct res_cou
if (*end != '\0')
goto out_free;
}
+ switch (member) {
+ case RES_LIMIT:
+ if (counter->ops.shrink_usage) {
+ ret = res_counter_resize_limit(counter, tmp);
+ goto done;
+ }
+ break;
+ default:
+ /*
+ * Considering future implementation, we'll have to handle
+ * other members and "fallback" will not work well. So, we
+ * avoid to make use of "default" here.
+ */
+ break;
+ }
spin_lock_irqsave(&counter->lock, flags);
val = res_counter_member(counter, member);
*val = tmp;
spin_unlock_irqrestore(&counter->lock, flags);
- ret = nbytes;
+ ret = 0;
+done:
+ if (!ret)
+ ret = nbytes;
out_free:
kfree(buf);
out:
Index: linux-2.6.26-rc5-mm3/Documentation/controllers/resource_counter.txt
===================================================================
--- linux-2.6.26-rc5-mm3.orig/Documentation/controllers/resource_counter.txt
+++ linux-2.6.26-rc5-mm3/Documentation/controllers/resource_counter.txt
@@ -39,7 +39,11 @@ to work with it.
The failcnt stands for "failures counter". This is the number of
resource allocation attempts that failed.

- c. spinlock_t lock
+ e. res_counter_ops.
+ Callbacks for helping resource_counter per each subsystem.
+ - shrink_usage() .... called at limit change (decrease).
+
+ f. spinlock_t lock

Protects changes of the above values.

@@ -141,8 +145,19 @@ counter fields. They are recommended to
failcnt reset to zero


+5. res_counter_ops (Callbacks)

-5. Usage example
+ res_counter_ops is for implementing feedback control from res_counter
+ to subsystem. Each one has each own purpose and the subsystem doesn't
+ necessary to provide all callbacks. Just implement necessary ones.
+
+ - shrink_usage(res_counter, newlimit, retry)
+ Called for reducing usage to newlimit, retry is incremented per
+ loop. (See memory resource controller as example.)
+ Returns 0 at success. Any error code is acceptable but -EBUSY will be
+ suitable to show "the kernel can't shrink usage."
+
+6. Usage example

a. Declare a task group (take a look at cgroups subsystem for this) and
fold a res_counter into it


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