Bug in reclaim logic with exhausted nodes?

Christoph Lameter cl at linux.com
Fri Apr 4 03:41:37 EST 2014

On Mon, 31 Mar 2014, Nishanth Aravamudan wrote:

> Yep. The node exists, it's just fully exhausted at boot (due to the
> presence of 16GB pages reserved at boot-time).

Well if you want us to support that then I guess you need to propose
patches to address this issue.

> I'd appreciate a bit more guidance? I'm suggesting that in this case the
> node functionally has no memory. So the page allocator should not allow
> allocations from it -- except (I need to investigate this still)
> userspace accessing the 16GB pages on that node, but that, I believe,
> doesn't go through the page allocator at all, it's all from hugetlb
> interfaces. It seems to me there is a bug in SLUB that we are noting
> that we have a useless per-node structure for a given nid, but not
> actually preventing requests to that node or reclaim because of those
> allocations.

Well if you can address that without impacting the fastpath then we could
do this. Otherwise we would need a fake structure here to avoid adding
checks to the fastpath

> I think there is a logical bug (even if it only occurs in this
> particular corner case) where if reclaim progresses for a THISNODE
> allocation, we don't check *where* the reclaim is progressing, and thus
> may falsely be indicating that we have done some progress when in fact
> the allocation that is causing reclaim will not possibly make any more
> progress.

Ok maybe we could address this corner case. How would you do this?

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