Commit 12b1c5f3 authored Jul 27, 2005 by Andy Whitcroft Committed by Linus Torvalds Jul 27, 2005

[PATCH] Remove bogus warning in page_alloc.c



Originally __free_pages_bulk used the relative page number within a zone to
define its buddies.  This meant that to maintain the "maximally aligned"
requirements (that an allocation of size N will be aligned at least to N
physically) zones had to also be aligned to 1<<MAX_ORDER pages.  When
__free_pages_bulk was updated to use the relative page frame numbers of the
free'd pages to pair buddies this released the alignment constraint on the
'left' edge of the zone.  This allows _either_ edge of the zone to contain
partial MAX_ORDER sized buddies.  These simply never will have matching
buddies and thus will never make it to the 'top' of the pyramid.

The patch below removes a now redundant check ensuring that the mem_map was
aligned to MAX_ORDER.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Cc: Christoph Lameter <christoph@lameter.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 165cd402

mm/page_alloc.c

+0 −4

Original line number	Diff line number	Diff line
		@@ -1861,7 +1861,6 @@ static void __init free_area_init_core(struct pglist_data *pgdat,
		unsigned long zones_size, unsigned long zholes_size)
		{
		unsigned long i, j;
		const unsigned long zone_required_alignment = 1UL << (MAX_ORDER-1);
		int cpu, nid = pgdat->node_id;
		unsigned long zone_start_pfn = pgdat->node_start_pfn;

		@@ -1934,9 +1933,6 @@ static void __init free_area_init_core(struct pglist_data *pgdat,
		zone->zone_mem_map = pfn_to_page(zone_start_pfn);
		zone->zone_start_pfn = zone_start_pfn;

		if ((zone_start_pfn) & (zone_required_alignment-1))
		printk(KERN_CRIT "BUG: wrong zone alignment, it will crash\n");

		memmap_init(size, nid, j, zone_start_pfn);

		zonetable_add(zone, nid, j, zone_start_pfn, size);

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