Re: [patch v2 2/2] s390: Add architecture code for unmapping crashkernel memory

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, Sep 14, 2011 at 10:58:28AM +0200, Michael Holzheu wrote:
> Hello Andrew,
> 
> On Tue, 2011-09-13 at 14:52 -0700, Andrew Morton wrote:
> > On Tue, 13 Sep 2011 15:26:37 +0200
> > Michael Holzheu <holzheu@linux.vnet.ibm.com> wrote:
> 
> [snip]
> 
> > > --- a/arch/s390/include/asm/kexec.h
> > > +++ b/arch/s390/include/asm/kexec.h
> > > @@ -36,6 +36,9 @@
> > >  /* Allocate one page for the pdp and the second for the code */
> > >  #define KEXEC_CONTROL_PAGE_SIZE 4096
> > >  
> > > +/* Alignment of crashkernel memory */
> > > +#define KEXEC_CRASH_MEM_ALIGN HPAGE_SIZE
> > 
> > Why not make this unconditional, for all architectures which support
> > hugepages?  ie:
> > 
> > #ifdef HPAGE_SIZE
> > #define KEXEC_CRASH_MEM_ALIGN HPAGE_SIZE
> > #else
> > #define KEXEC_CRASH_MEM_ALIGN PAGE_SIZE
> > #endif
> 
> > in include/linux/kexec.h?
> > 
> > IOW, what are the compromises here?
> 
> If we would do it that way, crashkernel memory on architectures that
> support large pages but do not support unmapping of crashkernel memory
> would always be aligned to HPAGE_SIZE. But only PAGE_SIZE alignment
> would be necessary in that case.
> 
> If that is acceptable I have no problem to define that unconditional for
> all architectures. Vivek what do you think?

As PAGE_SIZE alignment is sufficient for rest of the architecture, I 
am fine with keeping it in arch dependent files.

Thanks
Vivek