Re: [15/17] SLUB: Support virtual fallback via SLAB_VFALLBACK

From: Christoph Lameter
Date: Fri Sep 28 2007 - 14:41:34 EST

On Fri, 28 Sep 2007, Peter Zijlstra wrote:

> memory got massively fragemented, as anti-frag gets easily defeated.
> setting min_free_kbytes to 12M does seem to solve it - it forces 2 max
> order blocks to stay available, so we don't mix types. however 12M on
> 128M is rather a lot.

Yes, strict ordering would be much better. On NUMA it may be possible to
completely forbid merging. We can fall back to other nodes if necessary.
12M is not much on a NUMA system.

But this shows that (unsurprisingly) we may have issues on systems with a
small amounts of memory and we may not want to use higher orders on such

The case you got may be good to use as a testcase for the virtual
fallback. Hmmmm... Maybe it is possible to allocate the stack as a virtual
compound page. Got some script/code to produce that problem?
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