Re: [PATCH 3/3] mm: catch memory commitment underflow

Konstantin Khlebnikov
2014-06-26T04:08:52Z

On Thu, Jun 26, 2014 at 2:03 AM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Wed, 25 Jun 2014 00:16:14 +0400 Konstantin Khlebnikov <koct9i@gmail.com> wrote:
>
>> This patch prints warning (if CONFIG_DEBUG_VM=y) when
>> memory commitment becomes too negative.
>>
>> ...
>>
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -134,6 +134,12 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
>> {
>> unsigned long free, allowed, reserve;
>>
>> +#ifdef CONFIG_DEBUG_VM
>> + WARN_ONCE(percpu_counter_read(&vm_committed_as) <
>> + -(s64)vm_committed_as_batch * num_online_cpus(),
>> + "memory commitment underflow");
>> +#endif
>> +
>> vm_acct_memory(pages);
>
> The changelog doesn't describe the reasons for making the change.
>
> I assume this warning will detect the situation which the previous two
> patches just fixed?

Yep. Otherwise there is no way to validate these bugs, /proc/meminfo
hides negative values.

> Why not use VM_WARN_ON_ONCE()?

This patch is older than this macro.
Previously I've sent it in the last september and it was ignored. Now
I've found it again in my backlog.