[PATCH] percpu_counter_sum()
Andrew Morton [Wed, 8 Mar 2006 05:55:31 +0000 (21:55 -0800)]
Implement percpu_counter_sum().  This is a more accurate but slower version of
percpu_counter_read_positive().

We need this for Alex's speedup-ext3_statfs patch and for the nr_file
accounting fix.  Otherwise these things would be too inaccurate on large CPU
counts.

Cc: Ravikiran G Thirumalai <kiran@scalex86.org>
Cc: Alex Tomas <alex@clusterfs.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/percpu_counter.h
mm/swap.c

index bd6708e..6825255 100644 (file)
@@ -39,6 +39,7 @@ static inline void percpu_counter_destroy(struct percpu_counter *fbc)
 }
 
 void percpu_counter_mod(struct percpu_counter *fbc, long amount);
+long percpu_counter_sum(struct percpu_counter *fbc);
 
 static inline long percpu_counter_read(struct percpu_counter *fbc)
 {
@@ -92,6 +93,11 @@ static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
        return fbc->count;
 }
 
+static inline long percpu_counter_sum(struct percpu_counter *fbc)
+{
+       return percpu_counter_read_positive(fbc);
+}
+
 #endif /* CONFIG_SMP */
 
 static inline void percpu_counter_inc(struct percpu_counter *fbc)
index cce3dda..e9ec06d 100644 (file)
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -489,13 +489,34 @@ void percpu_counter_mod(struct percpu_counter *fbc, long amount)
        if (count >= FBC_BATCH || count <= -FBC_BATCH) {
                spin_lock(&fbc->lock);
                fbc->count += count;
+               *pcount = 0;
                spin_unlock(&fbc->lock);
-               count = 0;
+       } else {
+               *pcount = count;
        }
-       *pcount = count;
        put_cpu();
 }
 EXPORT_SYMBOL(percpu_counter_mod);
+
+/*
+ * Add up all the per-cpu counts, return the result.  This is a more accurate
+ * but much slower version of percpu_counter_read_positive()
+ */
+long percpu_counter_sum(struct percpu_counter *fbc)
+{
+       long ret;
+       int cpu;
+
+       spin_lock(&fbc->lock);
+       ret = fbc->count;
+       for_each_cpu(cpu) {
+               long *pcount = per_cpu_ptr(fbc->counters, cpu);
+               ret += *pcount;
+       }
+       spin_unlock(&fbc->lock);
+       return ret < 0 ? 0 : ret;
+}
+EXPORT_SYMBOL(percpu_counter_sum);
 #endif
 
 /*