[PATCH] x86: mm: clean up probe_memory_block_size()

[PATCH] x86: mm: clean up probe_memory_block_size()

[Seth Jennings]

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@variantweb.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)
 {
-	/* start from 2g */
-	unsigned long bz = 1UL<<31;
+	unsigned long bz = MIN_MEMORY_BLOCK_SIZE;
 
-	if (totalram_pages >= (64ULL << (30 - PAGE_SHIFT))) {
+	/* 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");
-		return 2UL * 1024 * 1024 * 1024;
+		bz = 2UL << 30; /* 2GB */
 	}
 
-	/* less than 64g installed */
-	if ((max_pfn << PAGE_SHIFT) < (16UL << 32))
-		return MIN_MEMORY_BLOCK_SIZE;
-
-	/* get the tail size */
-	while (bz > MIN_MEMORY_BLOCK_SIZE) {
-		if (!((max_pfn << PAGE_SHIFT) & (bz - 1)))
-			break;
-		bz >>= 1;
-	}
-
-	printk(KERN_DEBUG "memory block size : %ldMB\n", bz >> 20);
+	pr_debug("memory block size : %ldMB\n", bz >> 20);
 
 	return bz;
 }
-- 
2.5.0

Re: [PATCH] x86: mm: clean up probe_memory_block_size()

[Ingo Molnar]

* Seth Jennings <sjennings@variantweb.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@variantweb.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.

Thanks,

	Ingo

Re: [PATCH] x86: mm: clean up probe_memory_block_size()

[Seth Jennings]

On Thu, Nov 26, 2015 at 10:12:01AM +0100, Ingo Molnar wrote:
> 
> * Seth Jennings <sjennings@variantweb.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@variantweb.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