3.16.62-rc1 review patch. If anyone has any objections, please let me know.
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From: Dave Chinner dchinner@redhat.com
commit 80188b0d77d7426b494af739ac129e0e684acb84 upstream.
XFS uses non-stanard batch sizes for avoiding frequent global counter updates on it's allocated inode counters, as they increment or decrement in batches of 64 inodes. Hence the standard percpu counter batch of 32 means that the counter is effectively a global counter. Currently Xfs uses a batch size of 128 so that it doesn't take the global lock on every single modification.
However, Xfs also needs to compare accurately against zero, which means we need to use percpu_counter_compare(), and that has a hard-coded batch size of 32, and hence will spuriously fail to detect when it is supposed to use precise comparisons and hence the accounting goes wrong.
Add __percpu_counter_compare() to take a custom batch size so we can use it sanely in XFS and factor percpu_counter_compare() to use it.
Signed-off-by: Dave Chinner dchinner@redhat.com Acked-by: Tejun Heo tj@kernel.org Signed-off-by: Dave Chinner david@fromorbit.com Signed-off-by: Ben Hutchings ben@decadent.org.uk --- include/linux/percpu_counter.h | 13 ++++++++++++- lib/percpu_counter.c | 6 +++--- 2 files changed, 15 insertions(+), 4 deletions(-)
--- a/include/linux/percpu_counter.h +++ b/include/linux/percpu_counter.h @@ -40,7 +40,12 @@ void percpu_counter_destroy(struct percp 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); +int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch); + +static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs) +{ + return __percpu_counter_compare(fbc, rhs, percpu_counter_batch); +}
static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount) { @@ -114,6 +119,12 @@ static inline int percpu_counter_compare return 0; }
+static inline int +__percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) +{ + return percpu_counter_compare(fbc, rhs); +} + static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount) { --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -193,13 +193,13 @@ static int percpu_counter_hotcpu_callbac * 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) +int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) { 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 (abs(count - rhs) > (batch * num_online_cpus())) { if (count > rhs) return 1; else @@ -214,7 +214,7 @@ int percpu_counter_compare(struct percpu else return 0; } -EXPORT_SYMBOL(percpu_counter_compare); +EXPORT_SYMBOL(__percpu_counter_compare);
static int __init percpu_counter_startup(void) {