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Re: [Xen-devel] [RFC PATCH] ARM 32: Workaround for memory problem >1gb on last section

On Wed, 2014-10-01 at 11:37 +0100, Ian Campbell wrote:
> On Mon, 2014-09-29 at 17:02 +0100, Frediano Ziglio wrote:
> > setup_xenheap_mappings setup head memory on Arm 32 has a limit of 1GB.
> > On system with large memory is possible that there are no blocks of memory
> > smaller than 1gb leading xenheap_pages to be more than 1gb.
> > This cause memory errors trying to access heap after the 1gb limit.
> > 
> > I actually consider this patch as RFC as the pages are allocated at the end
> > of the block found however I don't think is safe to assume that the end is
> > aligned to 32mb as required.
> > 
> > Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

WRT the RFC and comment I think this patch is in and of itself correct.
I think the comment about no blocks of memory smaller than 1gb is a bit
misleading though, we will just look for a big enough region, so it's
actually the presence of large enough blocks not the absence of small
ones which is the problem.

The issue which you raise regarding the 32MB alignment is handled by the
call to consider_modules which takes 32MB as the required alignment
parameter, AFAIK it should return something which is suitably aligned,
since it aligns the end address on entry and eventually returns it. I'm
not 100% sure that it doesn't rely on size being 32MB aligned, but I my
99% sure it doesn't ;-).


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