Re: [PATCH] xen/arm: Workaround for memory problem >1gb

[Ian Campbell <Ian.Campbell@citrix.com>]

On Thu, 2014-10-02 at 12:03 +0100, Julien Grall wrote:
> Hello Frediano,
> 
> On 10/01/2014 03:27 PM, 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.
> > 
> > Signed-off-by: Frediano Ziglio <frediano.ziglio@huawei.com>
> > ---
> >  xen/arch/arm/setup.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> > index 446de8a..b1a43e6 100644
> > --- a/xen/arch/arm/setup.c
> > +++ b/xen/arch/arm/setup.c
> > @@ -524,6 +524,9 @@ static void __init setup_mm(unsigned long
> > dtb_paddr, size_t dtb_size)
> >      if ( ! e )
> >          panic("Not not enough space for xenheap");
> > 
> > +    if ( xenheap_pages > 1<<(30-PAGE_SHIFT) )
> > +        xenheap_pages = 1<<(30-PAGE_SHIFT);
> > +
> 
> Looking closer to the code, can't we add a new constraint before the
> loop when we are looking for the maximum heap size?
> 
> smth like:
> 
> xenheap_pages = (heap_pages/8 + ...)
> xenheap_pages = max(xenheap_pages, 128UL<<(20 - PAGE_SHIFT)
> xenheap_pages = max(xenheap_pages, 1UL<<(30-PAGE_SHIFT))

I think that would work, and it would have the additional benefit that
for some memory layouts it might cause us to place the xenheap in a
higher block of memory than we would otherwise, which is generally
desirable.

Ian.