diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h index d01351b1526f..8cb7c071bd5c 100644 --- a/include/linux/percpu_counter.h +++ b/include/linux/percpu_counter.h @@ -57,6 +57,8 @@ void percpu_counter_add_batch(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, s32 batch); +bool __percpu_counter_limited_add(struct percpu_counter *fbc, s64 limit, + s64 amount, s32 batch); void percpu_counter_sync(struct percpu_counter *fbc); static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs) @@ -69,6 +71,13 @@ static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount) percpu_counter_add_batch(fbc, amount, percpu_counter_batch); } +static inline bool +percpu_counter_limited_add(struct percpu_counter *fbc, s64 limit, s64 amount) +{ + return __percpu_counter_limited_add(fbc, limit, amount, + percpu_counter_batch); +} + /* * With percpu_counter_add_local() and percpu_counter_sub_local(), counts * are accumulated in local per cpu counter and not in fbc->count until @@ -185,6 +194,20 @@ percpu_counter_add(struct percpu_counter *fbc, s64 amount) local_irq_restore(flags); } +static inline bool +percpu_counter_limited_add(struct percpu_counter *fbc, s64 limit, s64 amount) +{ + unsigned long flags; + s64 count; + + local_irq_save(flags); + count = fbc->count + amount; + if (count <= limit) + fbc->count = count; + local_irq_restore(flags); + return count <= limit; +} + /* non-SMP percpu_counter_add_local is the same with percpu_counter_add */ static inline void percpu_counter_add_local(struct percpu_counter *fbc, s64 amount) diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index 9073430dc865..58a3392f471b 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -278,6 +278,59 @@ int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) } EXPORT_SYMBOL(__percpu_counter_compare); +/* + * Compare counter, and add amount if the total is within limit. + * Return true if amount was added, false if it would exceed limit. + */ +bool __percpu_counter_limited_add(struct percpu_counter *fbc, + s64 limit, s64 amount, s32 batch) +{ + s64 count; + s64 unknown; + unsigned long flags; + bool good; + + if (amount > limit) + return false; + + local_irq_save(flags); + unknown = batch * num_online_cpus(); + count = __this_cpu_read(*fbc->counters); + + /* Skip taking the lock when safe */ + if (abs(count + amount) <= batch && + fbc->count + unknown <= limit) { + this_cpu_add(*fbc->counters, amount); + local_irq_restore(flags); + return true; + } + + raw_spin_lock(&fbc->lock); + count = fbc->count + amount; + + /* Skip percpu_counter_sum() when safe */ + if (count + unknown > limit) { + s32 *pcount; + int cpu; + + for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) { + pcount = per_cpu_ptr(fbc->counters, cpu); + count += *pcount; + } + } + + good = count <= limit; + if (good) { + count = __this_cpu_read(*fbc->counters); + fbc->count += count + amount; + __this_cpu_sub(*fbc->counters, count); + } + + raw_spin_unlock(&fbc->lock); + local_irq_restore(flags); + return good; +} + static int __init percpu_counter_startup(void) { int ret; diff --git a/mm/shmem.c b/mm/shmem.c index 269cd3c1110f..61b170324e5c 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -217,15 +217,15 @@ static int shmem_inode_acct_blocks(struct inode *inode, long pages) might_sleep(); /* when quotas */ if (sbinfo->max_blocks) { - if (percpu_counter_compare(&sbinfo->used_blocks, - sbinfo->max_blocks - pages) > 0) + if (!percpu_counter_limited_add(&sbinfo->used_blocks, + sbinfo->max_blocks, pages)) goto unacct; err = dquot_alloc_block_nodirty(inode, pages); - if (err) + if (err) { + percpu_counter_sub(&sbinfo->used_blocks, pages); goto unacct; - - percpu_counter_add(&sbinfo->used_blocks, pages); + } } else { err = dquot_alloc_block_nodirty(inode, pages); if (err)