Re: [PATCH 0/5] make slab gfp fair

Peter Zijlstra
2007-05-17T21:27:57Z

On Thu, 2007-05-17 at 12:24 -0700, Christoph Lameter wrote:
> On Thu, 17 May 2007, Peter Zijlstra wrote:
>
> > The proposed patch doesn't change how the kernel functions at this
> > point; it just enforces an existing rule better.
>
> Well I'd say it controls the allocation failures. And that only works if
> one can consider the system having a single zone.
>
> Lets say the system has two cpusets A and B. A allocs from node 1 and B
> allocs from node 2. Two processes one in A and one in B run on the same
> processor.
>
> Node 1 gets very low in memory so your patch kicks in and sets up the
> global memory emergency situation with the reserve slab.
>
> Now the process in B will either fail although it has plenty of memory on
> node 2.
>
> Or it may just clear the emergency slab and then the next critical alloc
> of the process in A that is low on memory will fail.

The way I read the cpuset page allocator, it will only respect the
cpuset if there is memory aplenty. Otherwise it will grab whatever. So
still, it will only ever use ALLOC_NO_WATERMARKS if the whole system is
in distress.