linux-kernel - Re: [PATCH] x86: mm: clean up probe_memory_block

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Message-ID: <20151127023715.GA10427@cerebellum.local.variantweb.net>
Date:	Thu, 26 Nov 2015 20:37:15 -0600
From:	Seth Jennings <sjennings@...iantweb.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Peter Anvin <hpa@...or.com>,
	Daniel J Blueman <daniel@...ascale.com>,
	Yinghai Lu <yinghai@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: mm: clean up probe_memory_block_size()

On Thu, Nov 26, 2015 at 10:12:01AM +0100, Ingo Molnar wrote:
> 
> * Seth Jennings <sjennings@...iantweb.net> wrote:
> 
> > The cumulative effect of bdee237c and 982792c7 is some pretty convoluted
> > code.  This commit has no (intended) functional change; just seeks to
> > simplify and make the code more understandable.
> > 
> > The whole section with the "tail size" doesn't seem to be reachable,
> > since both the >= 64GB and < 64GB case return, so it was removed.
> > 
> > This commit also adds code back for the UV case since it seemed to just
> > go away without reason in bdee237c and might lead to unexpected change
> > in behavior.
> > 
> > Signed-off-by: Seth Jennings <sjennings@...iantweb.net>
> > ---
> >  arch/x86/mm/init_64.c | 22 ++++++----------------
> >  1 file changed, 6 insertions(+), 16 deletions(-)
> > 
> > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> > index ec081fe..a83c470 100644
> > --- a/arch/x86/mm/init_64.c
> > +++ b/arch/x86/mm/init_64.c
> > @@ -52,6 +52,7 @@
> >  #include <asm/numa.h>
> >  #include <asm/cacheflush.h>
> >  #include <asm/init.h>
> > +#include <asm/uv/uv.h>
> >  #include <asm/setup.h>
> >  
> >  #include "mm_internal.h"
> > @@ -1194,26 +1195,15 @@ int kern_addr_valid(unsigned long addr)
> >  
> >  static unsigned long probe_memory_block_size(void)
> >  {
> > +	unsigned long bz = MIN_MEMORY_BLOCK_SIZE;
> >  
> > +	/* if system is UV or has 64GB of RAM or more, use large blocks */
> > +	if (is_uv_system() || ((max_pfn << PAGE_SHIFT) >= (64UL << 30))) {
> >  		pr_info("Using 2GB memory block size for large-memory system\n");
> > +		bz = 2UL << 30; /* 2GB */
> >  	}
> >  
> > +	pr_debug("memory block size : %ldMB\n", bz >> 20);
> >  
> >  	return bz;
> >  }
> 
> So why keep 'bz' at all? Just return with the right value and be done with it. 
> 'bz' is just an unnecessary confusion factor.

Good point.  Just send out v2.

Thanks,
Seth

> 
> Thanks,
> 
> 	Ingo
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