Messages in this thread Patch in this message | | | Subject | [PATCH 2 of 4] hotplug-memory: adding non-section-aligned memory is bad | Date | Thu, 27 Mar 2008 17:28:38 -0700 | From | Jeremy Fitzhardinge <> |
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Adding non-section-aligned memory will cause bad results, because page structures are only built on section-aligned boundaries. Also, memory whose size isn't a multiple of the section size is silently ignored.
This patch adds a couple of WARN_ONs to help confused programmers work out what's going wrong when they hotplug memory without being aware of these constraints.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Yasunori Goto <y-goto@jp.fujitsu.com> Cc: Christoph Lameter <clameter@sgi.com> Cc: Dave Hansen <dave@linux.vnet.ibm.com>
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -784,6 +784,9 @@ #define PAGES_PER_SECTION (1UL << PFN_SECTION_SHIFT) #define PAGE_SECTION_MASK (~(PAGES_PER_SECTION-1)) +#define SECTION_SIZE (1UL << SECTION_SIZE_BITS) +#define SECTION_SIZE_MASK (SECTION_SIZE - 1) + #define SECTION_BLOCKFLAGS_BITS \ ((1UL << (PFN_SECTION_SHIFT - pageblock_order)) * NR_PAGEBLOCK_BITS) diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -300,6 +300,11 @@ int ret; u64 start = res->start; u64 size = res->end - res->start + 1; + + /* Adding non-section-aligned memory will give unexpected + and unintuitive results. */ + WARN_ON((start & SECTION_SIZE_MASK) != 0); + WARN_ON((size & SECTION_SIZE_MASK) != 0); if (!node_online(nid)) { pgdat = hotadd_new_pgdat(nid, start);
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