From 50bdd430c20566b13d8bc59946184b08f5875de6 Mon Sep 17 00:00:00 2001 From: Glauber Costa Date: Tue, 18 Dec 2012 14:22:04 -0800 Subject: [PATCH] res_counter: return amount of charges after res_counter_uncharge() It is useful to know how many charges are still left after a call to res_counter_uncharge. While it is possible to issue a res_counter_read after uncharge, this can be racy. If we need, for instance, to take some action when the counters drop down to 0, only one of the callers should see it. This is the same semantics as the atomic variables in the kernel. Since the current return value is void, we don't need to worry about anything breaking due to this change: nobody relied on that, and only users appearing from now on will be checking this value. Signed-off-by: Glauber Costa Reviewed-by: Michal Hocko Acked-by: Kamezawa Hiroyuki Acked-by: David Rientjes Cc: Johannes Weiner Cc: Suleiman Souhlal Cc: Tejun Heo Cc: Christoph Lameter Cc: Frederic Weisbecker Cc: Greg Thelen Cc: JoonSoo Kim Cc: Mel Gorman Cc: Pekka Enberg Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/cgroups/resource_counter.txt | 7 ++++--- include/linux/res_counter.h | 12 +++++++----- kernel/res_counter.c | 20 +++++++++++++------- 3 files changed, 24 insertions(+), 15 deletions(-) diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt index 0c4a344e78fa..c4d99ed0b418 100644 --- a/Documentation/cgroups/resource_counter.txt +++ b/Documentation/cgroups/resource_counter.txt @@ -83,16 +83,17 @@ to work with it. res_counter->lock internally (it must be called with res_counter->lock held). The force parameter indicates whether we can bypass the limit. - e. void res_counter_uncharge[_locked] + e. u64 res_counter_uncharge[_locked] (struct res_counter *rc, unsigned long val) When a resource is released (freed) it should be de-accounted from the resource counter it was accounted to. This is called - "uncharging". + "uncharging". The return value of this function indicate the amount + of charges still present in the counter. The _locked routines imply that the res_counter->lock is taken. - f. void res_counter_uncharge_until + f. u64 res_counter_uncharge_until (struct res_counter *rc, struct res_counter *top, unsinged long val) diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h index 6f54e40fa218..5ae8456d9670 100644 --- a/include/linux/res_counter.h +++ b/include/linux/res_counter.h @@ -125,14 +125,16 @@ int res_counter_charge_nofail(struct res_counter *counter, * * these calls check for usage underflow and show a warning on the console * _locked call expects the counter->lock to be taken + * + * returns the total charges still present in @counter. */ -void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val); -void res_counter_uncharge(struct res_counter *counter, unsigned long val); +u64 res_counter_uncharge_locked(struct res_counter *counter, unsigned long val); +u64 res_counter_uncharge(struct res_counter *counter, unsigned long val); -void res_counter_uncharge_until(struct res_counter *counter, - struct res_counter *top, - unsigned long val); +u64 res_counter_uncharge_until(struct res_counter *counter, + struct res_counter *top, + unsigned long val); /** * res_counter_margin - calculate chargeable space of a counter * @cnt: the counter diff --git a/kernel/res_counter.c b/kernel/res_counter.c index 3920d593e63c..ff55247e7049 100644 --- a/kernel/res_counter.c +++ b/kernel/res_counter.c @@ -86,33 +86,39 @@ int res_counter_charge_nofail(struct res_counter *counter, unsigned long val, return __res_counter_charge(counter, val, limit_fail_at, true); } -void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val) +u64 res_counter_uncharge_locked(struct res_counter *counter, unsigned long val) { if (WARN_ON(counter->usage < val)) val = counter->usage; counter->usage -= val; + return counter->usage; } -void res_counter_uncharge_until(struct res_counter *counter, - struct res_counter *top, - unsigned long val) +u64 res_counter_uncharge_until(struct res_counter *counter, + struct res_counter *top, + unsigned long val) { unsigned long flags; struct res_counter *c; + u64 ret = 0; local_irq_save(flags); for (c = counter; c != top; c = c->parent) { + u64 r; spin_lock(&c->lock); - res_counter_uncharge_locked(c, val); + r = res_counter_uncharge_locked(c, val); + if (c == counter) + ret = r; spin_unlock(&c->lock); } local_irq_restore(flags); + return ret; } -void res_counter_uncharge(struct res_counter *counter, unsigned long val) +u64 res_counter_uncharge(struct res_counter *counter, unsigned long val) { - res_counter_uncharge_until(counter, NULL, val); + return res_counter_uncharge_until(counter, NULL, val); } static inline unsigned long long * -- 2.20.1