Ravikiran G Thirumalai a écrit :
The spinlock in struct percpu_counter protects just one counter. It's
not obvious why it was done this way (I am guessing it was because earlier,
atomic_t was guaranteed 24 bits only on some arches). Since we have
atomic_long_t now, I don't see why this cannot be replaced with an atomic_t.
Comments?
Yes this makes sense.
Furthermore, we could try to fix 'struct percpu_counter' management (if SMP)
if alloc_percpu(long) call done in percpu_counter_init() fails. This is
currently ignored and can crash.
Something like (hybrid patch, to get the idea) :
--- a/mm/swap.c 2006-01-26 15:58:42.000000000 +0100
+++ b/mm/swap.c 2006-01-26 16:00:54.000000000 +0100
@@ -472,9 +472,12 @@
{
long count;
long *pcount;
- int cpu = get_cpu();
- pcount = per_cpu_ptr(fbc->counters, cpu);
+ if (unlikely(fbc->counters == NULL)) {
+ atomic_long_add(amount, &fbc->count);
+ return;
+ }
+ pcount = per_cpu_ptr(fbc->counters, get_cpu());
count = *pcount + amount;
if (count >= FBC_BATCH || count <= -FBC_BATCH) {
atomic_long_add(count, &fbc->count);
--- a/include/linux/percpu_counter.h 2006-01-26 16:02:31.000000000 +0100
+++ b/include/linux/percpu_counter.h 2006-01-26 16:02:53.000000000 +0100
@@ -35,7 +35,8 @@
static inline void percpu_counter_destroy(struct percpu_counter *fbc)
{
- free_percpu(fbc->counters);
+ if (fbc->counters)
+ free_percpu(fbc->counters);
}
void percpu_counter_mod(struct percpu_counter *fbc, long amount);
Eric
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