Date: Thu, 15 Nov 2007 02:39:43 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: mel@skynet.ie (Mel Gorman)
Cc: linuxppc-dev@ozlabs.org, sfr@canb.auug.org.au, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Fix boot problem with iSeries lacking hugepage support
Message-Id: <20071115023943.a54b0464.akpm@linux-foundation.org>
In-Reply-To: <20071115101322.GA5128@skynet.ie>
References: <20071115101322.GA5128@skynet.ie>
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On Thu, 15 Nov 2007 10:13:22 +0000 mel@skynet.ie (Mel Gorman) wrote:

> This patch is a fix for 2.6.24.
> 
> Ordinarily the size of a pageblock is determined at compile-time based on the
> hugepage size. On PPC64, the hugepage size is determined at runtime based on
> what is supported by the machine. With legacy machines such as iSeries that do
> not support hugepages, HPAGE_SHIFT becomes 0. This results in pageblock_order
> being set to -PAGE_SHIFT and a crash results shortly afterwards.
> 
> This patch sets HUGETLB_PAGE_SIZE_VARIABLE for PPC64 and adds a function
> to select a sensible value for pageblock order by default.  It checks that
> HPAGE_SHIFT is a sensible value before using the hugepage size; if it is
> not MAX_ORDER-1 is used.
> 
> Credit goes to Stephen Rothwell for identifying the bug and testing candidate
> patches.  Additional credit goes to Andy Whitcroft for spotting a problem
> with respects to IA-64 before releasing. Additional credit to David Gibson
> for testing with the libhugetlbfs test suite.
> 
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
> 
> --- 
>  arch/powerpc/Kconfig |    5 +++++
>  mm/page_alloc.c      |   14 ++++++++++++--
>  2 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.24-rc2-mm1-clean/arch/powerpc/Kconfig linux-2.6.24-rc2-005_iSeries_fix/arch/powerpc/Kconfig
> --- linux-2.6.24-rc2-mm1-clean/arch/powerpc/Kconfig	2007-11-14 11:38:05.000000000 +0000
> +++ linux-2.6.24-rc2-005_iSeries_fix/arch/powerpc/Kconfig	2007-11-14 11:39:12.000000000 +0000
> @@ -187,6 +187,11 @@ config FORCE_MAX_ZONEORDER
>  	default "9" if PPC_64K_PAGES
>  	default "13"
>  
> +config HUGETLB_PAGE_SIZE_VARIABLE
> +	bool
> +	depends on HUGETLB_PAGE
> +	default y
> +
>  config MATH_EMULATION
>  	bool "Math emulation"
>  	depends on 4xx || 8xx || E200 || PPC_MPC832x || E500
> diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.24-rc2-mm1-clean/mm/page_alloc.c linux-2.6.24-rc2-005_iSeries_fix/mm/page_alloc.c
> --- linux-2.6.24-rc2-mm1-clean/mm/page_alloc.c	2007-11-14 11:38:08.000000000 +0000
> +++ linux-2.6.24-rc2-005_iSeries_fix/mm/page_alloc.c	2007-11-14 13:45:19.000000000 +0000
> @@ -3342,6 +3342,16 @@ static void inline setup_usemap(struct p
>  #endif /* CONFIG_SPARSEMEM */
>  
>  #ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
> +
> +/* Return a sensible default order for the pageblock size. */
> +static inline int __init pageblock_default_order(void)
> +{
> +	if (HPAGE_SHIFT > PAGE_SHIFT)
> +		return HUGETLB_PAGE_ORDER;
> +
> +	return MAX_ORDER-1;
> +}
> +
>  /* Initialise the number of pages represented by NR_PAGEBLOCK_BITS */
>  static inline void __init set_pageblock_order(unsigned int order)
>  {
> @@ -3357,7 +3367,7 @@ static inline void __init set_pageblock_
>  }
>  #else /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
>  
> -/* Defined this way to avoid accidently referencing HUGETLB_PAGE_ORDER */
> +#define pageblock_default_order(x) (0)

Shouldn't this have been HUGETLB_PAGE_ORDER?

>  #define set_pageblock_order(x)	do {} while (0)
>  
>  #endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
> @@ -3442,7 +3452,7 @@ static void __meminit free_area_init_cor
>  		if (!size)
>  			continue;
>  
> -		set_pageblock_order(HUGETLB_PAGE_ORDER);
> +		set_pageblock_order(pageblock_default_order());
>  		setup_usemap(pgdat, zone, size);
>  		ret = init_currently_empty_zone(zone, zone_start_pfn,
>  						size, MEMMAP_EARLY);
> -- 
> -- 
> Mel Gorman
> Part-time Phd Student                          Linux Technology Center
> University of Limerick                         IBM Dublin Software Lab
-
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