mm: fix Committed_AS underflow on large NR_CPUS environment

The Committed_AS field can underflow in certain situations: > # while true; do cat /proc/meminfo | grep _AS; sleep 1; done | uniq -c > 1 Committed_AS: 18446744073709323392 kB > 11 Committed_AS: 18446744073709455488 kB > 6 Committed_AS: 35136 kB > 5 Committed_AS: 18446744073709454400 kB > 7 Committed_AS: 35904 kB > 3 Committed_AS: 18446744073709453248 kB > 2 Committed_AS: 34752 kB > 9 Committed_AS: 18446744073709453248 kB > 8 Committed_AS: 34752 kB > 3 Committed_AS: 18446744073709320960 kB > 7 Committed_AS: 18446744073709454080 kB > 3 Committed_AS: 18446744073709320960 kB > 5 Committed_AS: 18446744073709454080 kB > 6 Committed_AS: 18446744073709320960 kB Because NR_CPUS can be greater than 1000 and meminfo_proc_show() does not check for underflow. But NR_CPUS proportional isn't good calculation. In general, possibility of lock contention is proportional to the number of online cpus, not theorical maximum cpus (NR_CPUS). The current kernel has generic percpu-counter stuff. using it is right way. it makes code simplify and percpu_counter_read_positive() don't make underflow issue. Reported-by: Dave Hansen <[email protected]> Signed-off-by: KOSAKI Motohiro <[email protected]> Cc: Eric B Munson <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: <[email protected]> [All kernel versions] Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
berg · May 2, 2009 · 00a62ce · 00a62ce
1 parent 0763ed2
commit 00a62ce
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Showing 5 changed files with 17 additions and 65 deletions.
diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
@@ -35,7 +35,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
 #define K(x) ((x) << (PAGE_SHIFT - 10))
 	si_meminfo(&i);
 	si_swapinfo(&i);
-	committed = atomic_long_read(&vm_committed_space);
+	committed = percpu_counter_read_positive(&vm_committed_as);
 	allowed = ((totalram_pages - hugetlb_total_pages())
 		* sysctl_overcommit_ratio / 100) + total_swap_pages;
 

diff --git a/include/linux/mman.h b/include/linux/mman.h
@@ -12,21 +12,18 @@
 
 #ifdef __KERNEL__
 #include <linux/mm.h>
+#include <linux/percpu_counter.h>
 
 #include <asm/atomic.h>
 
 extern int sysctl_overcommit_memory;
 extern int sysctl_overcommit_ratio;
-extern atomic_long_t vm_committed_space;
+extern struct percpu_counter vm_committed_as;
 
-#ifdef CONFIG_SMP
-extern void vm_acct_memory(long pages);
-#else
 static inline void vm_acct_memory(long pages)
 {
-	atomic_long_add(pages, &vm_committed_space);
+	percpu_counter_add(&vm_committed_as, pages);
 }
-#endif
 
 static inline void vm_unacct_memory(long pages)
 {

diff --git a/mm/mmap.c b/mm/mmap.c
@@ -85,7 +85,7 @@ EXPORT_SYMBOL(vm_get_page_prot);
 int sysctl_overcommit_memory = OVERCOMMIT_GUESS;  /* heuristic overcommit */
 int sysctl_overcommit_ratio = 50;	/* default is 50% */
 int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
-atomic_long_t vm_committed_space = ATOMIC_LONG_INIT(0);
+struct percpu_counter vm_committed_as;
 
 /*
  * Check that a process has enough memory to allocate a new virtual
@@ -179,11 +179,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
 	if (mm)
 		allowed -= mm->total_vm / 32;
 
-	/*
-	 * cast `allowed' as a signed long because vm_committed_space
-	 * sometimes has a negative value
-	 */
-	if (atomic_long_read(&vm_committed_space) < (long)allowed)
+	if (percpu_counter_read_positive(&vm_committed_as) < allowed)
 		return 0;
 error:
 	vm_unacct_memory(pages);
@@ -2481,4 +2477,8 @@ void mm_drop_all_locks(struct mm_struct *mm)
  */
 void __init mmap_init(void)
 {
+	int ret;
+
+	ret = percpu_counter_init(&vm_committed_as, 0);
+	VM_BUG_ON(ret);
 }
diff --git a/mm/nommu.c b/mm/nommu.c
@@ -62,7 +62,7 @@ void *high_memory;
 struct page *mem_map;
 unsigned long max_mapnr;
 unsigned long num_physpages;
-atomic_long_t vm_committed_space = ATOMIC_LONG_INIT(0);
+struct percpu_counter vm_committed_as;
 int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
 int sysctl_overcommit_ratio = 50; /* default is 50% */
 int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
@@ -463,6 +463,10 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
  */
 void __init mmap_init(void)
 {
+	int ret;
+
+	ret = percpu_counter_init(&vm_committed_as, 0);
+	VM_BUG_ON(ret);
 	vm_region_jar = KMEM_CACHE(vm_region, SLAB_PANIC);
 }
 
@@ -1847,12 +1851,9 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
 	if (mm)
 		allowed -= mm->total_vm / 32;
 
-	/*
-	 * cast `allowed' as a signed long because vm_committed_space
-	 * sometimes has a negative value
-	 */
-	if (atomic_long_read(&vm_committed_space) < (long)allowed)
+	if (percpu_counter_read_positive(&vm_committed_as) < allowed)
 		return 0;
+
 error:
 	vm_unacct_memory(pages);
 

diff --git a/mm/swap.c b/mm/swap.c
@@ -491,49 +491,6 @@ unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
 
 EXPORT_SYMBOL(pagevec_lookup_tag);
 
-#ifdef CONFIG_SMP
-/*
- * We tolerate a little inaccuracy to avoid ping-ponging the counter between
- * CPUs
- */
-#define ACCT_THRESHOLD	max(16, NR_CPUS * 2)
-
-static DEFINE_PER_CPU(long, committed_space);
-
-void vm_acct_memory(long pages)
-{
-	long *local;
-
-	preempt_disable();
-	local = &__get_cpu_var(committed_space);
-	*local += pages;
-	if (*local > ACCT_THRESHOLD || *local < -ACCT_THRESHOLD) {
-		atomic_long_add(*local, &vm_committed_space);
-		*local = 0;
-	}
-	preempt_enable();
-}
-
-#ifdef CONFIG_HOTPLUG_CPU
-
-/* Drop the CPU's cached committed space back into the central pool. */
-static int cpu_swap_callback(struct notifier_block *nfb,
-			     unsigned long action,
-			     void *hcpu)
-{
-	long *committed;
-
-	committed = &per_cpu(committed_space, (long)hcpu);
-	if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
-		atomic_long_add(*committed, &vm_committed_space);
-		*committed = 0;
-		drain_cpu_pagevecs((long)hcpu);
-	}
-	return NOTIFY_OK;
-}
-#endif /* CONFIG_HOTPLUG_CPU */
-#endif /* CONFIG_SMP */
-
 /*
  * Perform any setup for the swap system
  */
@@ -554,7 +511,4 @@ void __init swap_setup(void)
 	 * Right now other parts of the system means that we
 	 * _really_ don't want to cluster much more
 	 */
-#ifdef CONFIG_HOTPLUG_CPU
-	hotcpu_notifier(cpu_swap_callback, 0);
-#endif
 }