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

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Message-ID: <20110914182902.GA32658@redhat.com>
Date:	Wed, 14 Sep 2011 14:29:02 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...gle.com>, ebiederm@...ssion.com,
	mahesh@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
	heiko.carstens@...ibm.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch v2 2/2] s390: Add architecture code for unmapping
 crashkernel memory

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@...ux.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
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