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

[Austin S. Hemmelgarn]

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.