Re: [Xen-devel] [PATCH] xen: arm: reduce the size of the xen heap to max 1/8 RAM size

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-07-23 at 18:15 +0100, Ian Campbell wrote:
> Hi Keir,
> 
> Was I mistaken about the domheap->xenheap fallback or have we cocked
> something up on ARM?

Tim told me IRL that the fallback is deliberately not there. So I think
this patch is correct.

@arm folks: ping ;-)

> 
> Cheers,
> Ian.
> 
> On Tue, 2013-07-23 at 18:12 +0100, Ian Campbell wrote:
> > From: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > 
> > When building a 1GB dom0 on a system with 2GB RAM we are running out of 
> > domheap
> > pages, while there are still plenty of xenheap pages spare.
> > 
> > I would have sworn that when the domheap was exhausted we would fall back to
> > allocating xenheap pages but this doesn't appear to be the case. It's 
> > possible
> > that we have setup something incorrectly on ARM but alloc_domheap_pages 
> > pretty
> > clearly tries to allocate memory from MEMZONE_XEN+1..zone_hi.
> > 
> > Without the fallback from domheap to xenheap taking 1GB of any system with 
> > >1GB
> > of RAM for xenheap is excessive so instead set a limit of 1/8 of the total
> > amount of RAM. By way of comparison x86_32 used to have a static 12MB 
> > xenheap
> > (which also included .text etc) and in theory supported up to 16GB RAM, by 
> > that
> > measure 1/8 is plenty.
> > 
> > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > Cc: keir@xxxxxxx
> > ---
> >  xen/arch/arm/setup.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> > index 2f9fdc8..195c28e 100644
> > --- a/xen/arch/arm/setup.c
> > +++ b/xen/arch/arm/setup.c
> > @@ -316,14 +316,14 @@ static void __init setup_mm(unsigned long dtb_paddr, 
> > size_t dtb_size)
> >       *
> >       *  - must be 32 MiB aligned
> >       *  - must not include Xen itself or the boot modules
> > -     *  - must be at most 1 GiB
> > +     *  - must be at most 1/8 the total RAM in the system
> >       *  - must be at least 128M
> >       *
> >       * We try to allocate the largest xenheap possible within these
> >       * constraints.
> >       */
> >      heap_pages = (ram_size >> PAGE_SHIFT);
> > -    xenheap_pages = min(1ul << (30 - PAGE_SHIFT), heap_pages);
> > +    xenheap_pages = max(heap_pages/8, 128UL<<(20-PAGE_SHIFT));
> >  
> >      do
> >      {
> 
> 
> 
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