[Xen-devel] dom0 boot failure: dma_reserve in reserve_bootmem_generic()

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 26.06.10 at 03:40, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> So, anyone know the point of setting dma_reserve? Obviously, things 

I think the comment immediately before set_dma_reserve() explains
it quite well:

 * The per-cpu batchsize and zone watermarks are determined by present_pages.
 * In the DMA zone, a significant percentage may be consumed by kernel image
 * and other unfreeable allocations which can skew the watermarks badly. This
 * function may optionally be used to account for unfreeable pages in the
 * first zone (e.g., ZONE_DMA). The effect will be lower watermarks and
 * smaller per-cpu batchsize.

> are implied OK without it, so would it be safe to just remove the
> if stmt completely?

In all our post-2.6.18 kernels we indeed have this disabled, and
didn't have any issue with it so far. Nevertheless I'm not convinced
us really doing a good thing with disabling it after the change (a
pretty long while ago) to no longer put all memory in the DMA zone.

For your issue, I rather wonder why dma_reserve reaches this high
a value only with the particular dom0_mem= you're stating. Did
you check where those reservations come from, and how they
 differfrom when using smaller or larger dom0_mem= values?

Jan


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