Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19

Martin J. Bligh
2005-10-31T19:40:52Z

--On Monday, October 31, 2005 11:24:09 -0800 Andrew Morton <akpm@osdl.org> wrote:

> "Martin J. Bligh" <mbligh@mbligh.org> wrote:
>>
>> To me, the question is "do we support higher order allocations, or not?".
>> Pretending we do, making a half-assed job of it, and then it not working
>> well under pressure is not helping anyone. I'm told, for instance, that
>> AMD64 requires > 4K stacks - that's pretty fundamental, as just one
>> instance. I'd rather make Linux pretty bulletproof - the added feature
>> stuff is just a bonus that comes for free with that.
>
> Well... stacks are allocated with GFP_KERNEL, so we're reliable there.
>
> It's the GFP_ATOMIC higher-order allocations which fail, and networking
> copes with that.
>
> I suspect this would all be a non-issue if the net drivers were using
> __GFP_NOWARN ;)

We still need to allocate them, even if it's GFP_KERNEL. As memory gets
larger and larger, and we have no targetted reclaim, we'll have to blow
away more and more stuff at random before we happen to get contiguous
free areas. Just statistics aren't in your favour ... Getting 4 contig
pages on a 1GB desktop is much harder than on a 128MB machine.

Is not going to get better as time goes on ;-) Yeah, yeah, I know, you
want recreates, numbers, etc. Not the easiest thing to reproduce in a
short-term consistent manner though.

M.