On Sep 29, 2006, at 12:25 AM, Amos Waterland wrote:

At dom0_mem 2G and 7G, we get:

(XEN) Cannot handle page request order 13!
(XEN) ****************************************
(XEN) Panic on CPU 0:
(XEN) shadow allocation failed 0x0 < 0x20
(XEN) ****************************************

Oh of course, we allocate the "shadow" (HTAB) for dom0 as 1/64th of dom0_mem. This currently gets allocated from the Xen heap, which cannot accommodate a 32M aligned & contiguous memory. The Xen heap is 64M minus images (about 56M + 4M) but the allocator has been used its unclear what is truly available at the time of this allocation.

Hollis has been bugging me that shadow should come from the Dom heap, but I wanted to avoid allocating aligned multi-megs from here since it will seriously effect the number of domains we can create. Nut It never really dawned on me that 1/64 would get this big.

We could:
1) Allocate from Dom Heap, unpredictably limiting the amount of memory/domains we can actually use. 2) Detect that on large memory systems we increase the Xen heap (subject to RMA sizes). 3) Set aside Dom Heap memory and manage htab allocations separately, and at least is predictable. 4) Use a new heap Zone for htabs, perhaps borrowing from the non- DMAable Dom Zone which we do not use.

(4) is like (3) but tries to reuse the existing allocator
(4) (or 3) sound good to me, thoughts?


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