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authorTim Chen <tim.c.chen@linux.intel.com>2010-08-09 17:19:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-08-09 20:44:58 -0700
commit27f5e0f694fd0600274a76854636c0749e3bb1f6 (patch)
tree0d3a0387b42eb0a830fa5ba896a205b2a3807b8b /lib
parent4e60c86bd9e5a7110ed28874d0b6592186550ae8 (diff)
tmpfs: add accurate compare function to percpu_counter library
Add percpu_counter_compare that allows for a quick but accurate comparison of percpu_counter with a given value. A rough count is provided by the count field in percpu_counter structure, without accounting for the other values stored in individual cpu counters. The actual count is a sum of count and the cpu counters. However, count field is never different from the actual value by a factor of batch*num_online_cpu. We do not need to get actual count for comparison if count is different from the given value by this factor and allows for quick comparison without summing up all the per cpu counters. Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/percpu_counter.c27
1 files changed, 27 insertions, 0 deletions
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index aeaa6d734447..ec9048e74f44 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -137,6 +137,33 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
return NOTIFY_OK;
}
+/*
+ * Compare counter against given value.
+ * Return 1 if greater, 0 if equal and -1 if less
+ */
+int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
+{
+ s64 count;
+
+ count = percpu_counter_read(fbc);
+ /* Check to see if rough count will be sufficient for comparison */
+ if (abs(count - rhs) > (percpu_counter_batch*num_online_cpus())) {
+ if (count > rhs)
+ return 1;
+ else
+ return -1;
+ }
+ /* Need to use precise count */
+ count = percpu_counter_sum(fbc);
+ if (count > rhs)
+ return 1;
+ else if (count < rhs)
+ return -1;
+ else
+ return 0;
+}
+EXPORT_SYMBOL(percpu_counter_compare);
+
static int __init percpu_counter_startup(void)
{
compute_batch_value();

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