Re: [Qemu-devel] [PATCH 6/6] kvm: Fix dirty tracking with large kernel page size

[David Gibson <david@gibson.dropbear.id.au>]

On Wed, Feb 29, 2012 at 12:32:51AM +0100, Alexander Graf wrote:
> 
> On 24.02.2012, at 01:23, David Gibson wrote:
> 
> > From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > 
> > If the kernel page size is larger than TARGET_PAGE_SIZE, which
> > happens for example on ppc64 with kernels compiled for 64K pages,
> > the dirty tracking doesn't work.
> > 
> > Cc: Avi Kivity <avi@redhat.com>
> > Cc: Marcelo Tossatti <mtossatti@redhat.com>
> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> > kvm-all.c |    7 ++++---
> > 1 files changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kvm-all.c b/kvm-all.c
> > index 5e188bf..3f8cfd9 100644
> > --- a/kvm-all.c
> > +++ b/kvm-all.c
> > @@ -348,10 +348,11 @@ static int kvm_set_migration_log(int enable)
> > static int kvm_get_dirty_pages_log_range(MemoryRegionSection *section,
> >                                          unsigned long *bitmap)
> > {
> > -    unsigned int i, j;
> > +  unsigned int i, j;
> >     unsigned long page_number, c;
> >     target_phys_addr_t addr, addr1;
> >     unsigned int len = ((section->size / TARGET_PAGE_SIZE) + HOST_LONG_BITS - 1) / HOST_LONG_BITS;
> > +    unsigned long hpratio = getpagesize() / TARGET_PAGE_SIZE;
> 
> Actually, looking at this, don't we rather want to cache hpratio?
> The way this is implemented, it would mean we'd do a sysctl for
> every call, right?

I think libc already caches this.

-- 
David Gibson			| I'll have my music baroque, and my code
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