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Commit 55878e88 authored by Cody P Schafer's avatar Cody P Schafer Committed by Linus Torvalds
Browse files

sparsemem: add BUILD_BUG_ON when sizeof mem_section is non-power-of-2 

Instead of leaving a hidden trap for the next person who comes along and
wants to add something to mem_section, add a big fat warning about it
needing to be a power-of-2, and insert a BUILD_BUG_ON() in sparse_init()
to catch mistakes.

Right now non-power-of-2 mem_sections cause a number of WARNs at boot
(which don't clearly point to the size of mem_section as an issue), but
the system limps on (temporarily, at least).

This is based upon Dave Hansen's earlier RFC where he ran into the same
issue:
	"sparsemem: fix boot when SECTIONS_PER_ROOT is not power-of-2"
	http://lkml.indiana.edu/hypermail/linux/kernel/1205.2/03077.html



Signed-off-by: default avatarCody P Schafer <cody@linux.vnet.ibm.com>
Acked-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Cc: Jiang Liu <liuj97@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b26a3dfd

include/linux/mmzone.h

+4 −0
Original line number Diff line number Diff line
@@ -1137,6 +1137,10 @@ struct mem_section { 
	struct page_cgroup *page_cgroup;

	unsigned long pad;

#endif

	/*

	 * WARNING: mem_section must be a power-of-2 in size for the

	 * calculation and use of SECTION_ROOT_MASK to make sense.

	 */

};



#ifdef CONFIG_SPARSEMEM_EXTREME

mm/sparse.c

+3 −0
Original line number Diff line number Diff line
@@ -481,6 +481,9 @@ void __init sparse_init(void) 
	struct page **map_map;

#endif



	/* see include/linux/mmzone.h 'struct mem_section' definition */

	BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));



	/* Setup pageblock_order for HUGETLB_PAGE_SIZE_VARIABLE */

	set_pageblock_order();