[patch 107/163] percpu_counter: add percpu_counter_sync()

Andrew Morton
2020-08-07T06:23:15Z

From: Feng Tang <feng.tang@intel.com>
Subject: percpu_counter: add percpu_counter_sync()

percpu_counter's accuracy is related to its batch size. For a
percpu_counter with a big batch, its deviation could be big, so when the
counter's batch is runtime changed to a smaller value for better accuracy,
there could also be requirment to reduce the big deviation.

So add a percpu-counter sync function to be run on each CPU.

Link: http://lkml.kernel.org/r/1594389708-60781-4-git-send-email-feng.tang@intel.com
Signed-off-by: Feng Tang <feng.tang@intel.com>
Reported-by: kernel test robot <rong.a.chen@intel.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Andi Kleen <andi.kleen@intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Tim Chen <tim.c.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/percpu_counter.h | 4 ++++
lib/percpu_counter.c | 19 +++++++++++++++++++
2 files changed, 23 insertions(+)

--- a/include/linux/percpu_counter.h~percpu_counter-add-percpu_counter_sync
+++ a/include/linux/percpu_counter.h
@@ -44,6 +44,7 @@ void percpu_counter_add_batch(struct per
s32 batch);
s64 __percpu_counter_sum(struct percpu_counter *fbc);
int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch);
+void percpu_counter_sync(struct percpu_counter *fbc);

static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
{
@@ -172,6 +173,9 @@ static inline bool percpu_counter_initia
return true;
}

+static inline void percpu_counter_sync(struct percpu_counter *fbc)
+{
+}
#endif /* CONFIG_SMP */

static inline void percpu_counter_inc(struct percpu_counter *fbc)
--- a/lib/percpu_counter.c~percpu_counter-add-percpu_counter_sync
+++ a/lib/percpu_counter.c
@@ -99,6 +99,25 @@ void percpu_counter_add_batch(struct per
EXPORT_SYMBOL(percpu_counter_add_batch);

/*
+ * For percpu_counter with a big batch, the devication of its count could
+ * be big, and there is requirement to reduce the deviation, like when the
+ * counter's batch could be runtime decreased to get a better accuracy,
+ * which can be achieved by running this sync function on each CPU.
+ */
+void percpu_counter_sync(struct percpu_counter *fbc)
+{
+ unsigned long flags;
+ s64 count;
+
+ raw_spin_lock_irqsave(&fbc->lock, flags);
+ count = __this_cpu_read(*fbc->counters);
+ fbc->count += count;
+ __this_cpu_sub(*fbc->counters, count);
+ raw_spin_unlock_irqrestore(&fbc->lock, flags);
+}
+EXPORT_SYMBOL(percpu_counter_sync);
+
+/*
* Add up all the per-cpu counts, return the result. This is a more accurate
* but much slower version of percpu_counter_read_positive()
*/
_