Re: [PATCH] mm: add config option to select the initial overcommit mode

Austin S. Hemmelgarn
2016-05-13T14:14:59Z

On 2016-05-13 09:34, Sebastian Frias wrote:
> Hi Austin,
>
> On 05/13/2016 03:11 PM, Austin S. Hemmelgarn wrote:
>> On 2016-05-13 08:39, Sebastian Frias wrote:
>>>
>>> My point is that it seems to be possible to deal with such conditions in a more controlled way, ie: a way that is less random and less abrupt.
>> There's an option for the OOM-killer to just kill the allocating task instead of using the scoring heuristic. This is about as deterministic as things can get though.
>
> By the way, why does it has to "kill" anything in that case?
> I mean, shouldn't it just tell the allocating task that there's not enough memory by letting malloc return NULL?
In theory, that's a great idea. In practice though, it only works if:
1. The allocating task correctly handles malloc() (or whatever other
function it uses) returning NULL, which a number of programs don't.
2. The task actually has fallback options for memory limits. Many
programs that do handle getting a NULL pointer from malloc() handle it
by exiting anyway, so there's not as much value in this case.
3. There isn't a memory leak somewhere on the system. Killing the
allocating task doesn't help much if this is the case of course.

You have to keep in mind though, that on a properly provisioned system,
the only situations where the OOM killer should be invoked are when
there's a memory leak, or when someone is intentionally trying to DoS
the system through memory exhaustion. If you're hitting the OOM killer
for any other reason than those or a kernel bug, then you just need more
memory or more swap space.