Re: [PATCH] mm: setup pageblock_order before it's used by sparse

[Yinghai Lu <yinghai@kernel.org>]

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On Sat, Jun 30, 2012 at 2:07 AM, Jiang Liu <jiang.liu@huawei.com> wrote:
> From: Xishi Qiu <qiuxishi@huawei.com>
>
> On architectures with CONFIG_HUGETLB_PAGE_SIZE_VARIABLE set, such as Itanium,
> pageblock_order is a variable with default value of 0. It's set to the right
> value by set_pageblock_order() in function free_area_init_core().
>
> But pageblock_order may be used by sparse_init() before free_area_init_core()
> is called along path:
> sparse_init()
>    ->sparse_early_usemaps_alloc_node()
>        ->usemap_size()
>            ->SECTION_BLOCKFLAGS_BITS
>                ->((1UL << (PFN_SECTION_SHIFT - pageblock_order)) *
> NR_PAGEBLOCK_BITS)
>
> The uninitialized pageblock_size will cause memory wasting because usemap_size()
> returns a much bigger value then it's really needed.
>
> For example, on an Itanium platform,
> sparse_init() pageblock_order=0 usemap_size=24576
> free_area_init_core() before pageblock_order=0, usemap_size=24576
> free_area_init_core() after pageblock_order=12, usemap_size=8
>
> That means 24K memory has been wasted for each section, so fix it by calling
> set_pageblock_order() from sparse_init().
>

can you check attached patch?

That will kill more lines code instead.

Thanks

Yinghai

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Subject: [PATCH] mm: set pageblock_order in compiling time

That is initial setting, and could be override by command line.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
 mm/page_alloc.c |   45 ++++++---------------------------------------
 1 file changed, 6 insertions(+), 39 deletions(-)

Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c
+++ linux-2.6/mm/page_alloc.c
@@ -147,7 +147,12 @@ bool pm_suspended_storage(void)
 #endif /* CONFIG_PM_SLEEP */
 
 #ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
-int pageblock_order __read_mostly;
+/*
+ * Assume the largest contiguous order of interest is a huge page.
+ * This value may be variable depending on boot parameters on IA64 and
+ * powerpc.
+ */
+int pageblock_order = ((HPAGE_SHIT > PAGE_SHIFT) ? HUGETLB_PAGE_ORDER : (MAX_ORDER - 1)) __read_mostly;
 #endif
 
 static void __free_pages_ok(struct page *page, unsigned int order);
@@ -4298,43 +4303,6 @@ static inline void setup_usemap(struct p
 				struct zone *zone, unsigned long zonesize) {}
 #endif /* CONFIG_SPARSEMEM */
 
-#ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
-
-/* Initialise the number of pages represented by NR_PAGEBLOCK_BITS */
-static inline void __init set_pageblock_order(void)
-{
-	unsigned int order;
-
-	/* Check that pageblock_nr_pages has not already been setup */
-	if (pageblock_order)
-		return;
-
-	if (HPAGE_SHIFT > PAGE_SHIFT)
-		order = HUGETLB_PAGE_ORDER;
-	else
-		order = MAX_ORDER - 1;
-
-	/*
-	 * Assume the largest contiguous order of interest is a huge page.
-	 * This value may be variable depending on boot parameters on IA64 and
-	 * powerpc.
-	 */
-	pageblock_order = order;
-}
-#else /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
-
-/*
- * When CONFIG_HUGETLB_PAGE_SIZE_VARIABLE is not set, set_pageblock_order()
- * is unused as pageblock_order is set at compile-time. See
- * include/linux/pageblock-flags.h for the values of pageblock_order based on
- * the kernel config
- */
-static inline void set_pageblock_order(void)
-{
-}
-
-#endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
-
 /*
  * Set up the zone data structures:
  *   - mark all pages reserved
@@ -4413,7 +4381,6 @@ static void __paginginit free_area_init_
 		if (!size)
 			continue;
 
-		set_pageblock_order();
 		setup_usemap(pgdat, zone, size);
 		ret = init_currently_empty_zone(zone, zone_start_pfn,
 						size, MEMMAP_EARLY);