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

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Date:	Thu, 26 Jun 2014 08:08:50 +0400
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Hugh Dickins <hughd@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm: catch memory commitment underflow

On Thu, Jun 26, 2014 at 2:03 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 25 Jun 2014 00:16:14 +0400 Konstantin Khlebnikov <koct9i@...il.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.
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