lib: percpu_counter variable batch

Because the current batch setup has an quadric error bound on the counter,
allow for an alternative setup.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 12 insertions, 4 deletions

diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 438a170187ec..40df86f7a3b4 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -32,9 +32,14 @@ struct percpu_counter {
 
 void percpu_counter_init(struct percpu_counter *fbc, s64 amount);
 void percpu_counter_destroy(struct percpu_counter *fbc);
-void percpu_counter_add(struct percpu_counter *fbc, s32 amount);
+void __percpu_counter_add(struct percpu_counter *fbc, s32 amount, s32 batch);
 s64 percpu_counter_sum(struct percpu_counter *fbc);
 
+static inline void percpu_counter_add(struct percpu_counter *fbc, s32 amount)
+{
+        __percpu_counter_add(fbc, amount, FBC_BATCH);
+}
+
 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
 {
         return fbc->count;
@@ -70,6 +75,9 @@ static inline void percpu_counter_destroy(struct percpu_counter *fbc)
 {
 }
 
+#define __percpu_counter_add(fbc, amount, batch) \
+        percpu_counter_add(fbc, amount)
+
 static inline void
 percpu_counter_add(struct percpu_counter *fbc, s32 amount)
 {
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 5f36ad79a24a..f736d67c64d7 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -14,7 +14,7 @@ static LIST_HEAD(percpu_counters);
 static DEFINE_MUTEX(percpu_counters_lock);
 #endif
 
-void percpu_counter_add(struct percpu_counter *fbc, s32 amount)
+void __percpu_counter_add(struct percpu_counter *fbc, s32 amount, s32 batch)
 {
         long count;
         s32 *pcount;
@@ -22,7 +22,7 @@ void percpu_counter_add(struct percpu_counter *fbc, s32 amount)
 
         pcount = per_cpu_ptr(fbc->counters, cpu);
         count = *pcount + amount;
-        if (count >= FBC_BATCH || count <= -FBC_BATCH) {
+        if (count >= batch || count <= -batch) {
                 spin_lock(&fbc->lock);
                 fbc->count += count;
                 *pcount = 0;
@@ -32,7 +32,7 @@ void percpu_counter_add(struct percpu_counter *fbc, s32 amount)
         }
         put_cpu();
 }
-EXPORT_SYMBOL(percpu_counter_add);
+EXPORT_SYMBOL(__percpu_counter_add);
 
 /*
  * Add up all the per-cpu counts, return the result.  This is a more accurate