From 27f5e0f694fd0600274a76854636c0749e3bb1f6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 9 Aug 2010 17:19:04 -0700 Subject: [PATCH] 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 Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/percpu_counter.h | 11 +++++++++++ lib/percpu_counter.c | 27 +++++++++++++++++++++++++++ 2 files changed, 38 insertions(+) diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h index c88d67b5939..8a7d510ffa9 100644 --- a/include/linux/percpu_counter.h +++ b/include/linux/percpu_counter.h @@ -40,6 +40,7 @@ void percpu_counter_destroy(struct percpu_counter *fbc); void percpu_counter_set(struct percpu_counter *fbc, s64 amount); void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch); s64 __percpu_counter_sum(struct percpu_counter *fbc); +int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs); static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount) { @@ -98,6 +99,16 @@ static inline void percpu_counter_set(struct percpu_counter *fbc, s64 amount) fbc->count = amount; } +static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs) +{ + if (fbc->count > rhs) + return 1; + else if (fbc->count < rhs) + return -1; + else + return 0; +} + static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount) { diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index aeaa6d73444..ec9048e74f4 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(); -- 2.20.1