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Commit 00a62ce9 authored by KOSAKI Motohiro's avatar KOSAKI Motohiro Committed by Linus Torvalds
Browse files

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: default avatarDave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Eric B Munson <ebmunson@us.ibm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: <stable@kernel.org>		[All kernel versions]
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0763ed23

fs/proc/meminfo.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

include/linux/mman.h

+3 −6
Original line number Diff line number Diff line
@@ -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)

{

mm/mmap.c

+6 −6
Original line number Diff line number Diff line
@@ -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);

}

mm/nommu.c

+7 −6
Original line number Diff line number Diff line
@@ -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);

mm/swap.c

+0 −46
Original line number Diff line number Diff line
@@ -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

}