Re: [PATCH 02/10] mm: system wide ALLOC_NO_WATERMARK

Peter Zijlstra
2007-08-06T18:31:02Z

On Mon, 2007-08-06 at 11:21 -0700, Daniel Phillips wrote:
> On Monday 06 August 2007 11:11, Christoph Lameter wrote:
> > On Mon, 6 Aug 2007, Peter Zijlstra wrote:
> > > Change ALLOC_NO_WATERMARK page allocation such that dipping into
> > > the reserves becomes a system wide event.
> >
> > Shudder. That can just be a desaster for NUMA. Both performance wise
> > and logic wise. One cpuset being low on memory should not affect
> > applications in other cpusets.

Do note that these are only PF_MEMALLOC allocations that will break the
cpuset. And one can argue that these are not application allocation but
system allocations.

> Currently your system likely would have died here, so ending up with a
> reserve page temporarily on the wrong node is already an improvement.
>
> I agree that the reserve pool should be per-node in the end, but I do
> not think that serves the interest of simplifying the initial patch
> set. How about a numa performance patch that adds onto the end of
> Peter's series?

Trouble with keeping this per node is that all the code dealing with the
reserve needs to keep per-cpu state, which given that the system is
really crawling at that moment, seems excessive.