linux-kernel - Re: [BUGFIX][PATCH] Fix usemap initialization v3

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Date:	Wed, 23 Apr 2008 13:46:20 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, Hugh Dickins <hugh@...itas.com>,
	Shi Weihua <shiwh@...fujitsu.com>, balbir@...ux.vnet.ibm.com,
	xemul@...nvz.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [BUGFIX][PATCH] Fix usemap initialization v3

On (23/04/08 13:46), KAMEZAWA Hiroyuki didst pronounce:
> fixed typos.
> ==
> usemap must be initialized only when pfn is within zone.
> If not, it corrupts memory.
> 
> And this patch also reduces the number of calls to set_pageblock_migratetype()
> from
> 	(pfn & (pageblock_nr_pages -1)
> to
> 	!(pfn & (pageblock_nr_pages-1)
> it should be called once per pageblock.
> 

Nicely spotted.

> Changelog.
> v2->v3
>  - Fixed typos.
> v1->v2
>  - Fixed boundary check.
>  - Move calculation of pointer for zone struct to out of loop.
> 
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> ---
>  mm/page_alloc.c |   14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6.25/mm/page_alloc.c
> ===================================================================
> --- linux-2.6.25.orig/mm/page_alloc.c
> +++ linux-2.6.25/mm/page_alloc.c
> @@ -2518,7 +2518,9 @@ void __meminit memmap_init_zone(unsigned
>  	struct page *page;
>  	unsigned long end_pfn = start_pfn + size;
>  	unsigned long pfn;
> +	struct zone *z;
>  
> +	z = &NODE_DATA(nid)->node_zones[zone];
>  	for (pfn = start_pfn; pfn < end_pfn; pfn++) {

Ok, this is fine. zone being an index instead of a struct zone is a
little confusing but it's not your fault.

>  		/*
>  		 * There can be holes in boot-time mem_map[]s
> @@ -2536,7 +2538,6 @@ void __meminit memmap_init_zone(unsigned
>  		init_page_count(page);
>  		reset_page_mapcount(page);
>  		SetPageReserved(page);
> -
>  		/*
>  		 * Mark the block movable so that blocks are reserved for
>  		 * movable at startup. This will force kernel allocations

Spurious whitespace change there.

> @@ -2545,8 +2546,15 @@ void __meminit memmap_init_zone(unsigned
>  		 * kernel allocations are made. Later some blocks near
>  		 * the start are marked MIGRATE_RESERVE by
>  		 * setup_zone_migrate_reserve()
> +		 *
> +		 * bitmap is created for zone's valid pfn range. but memmap
> +		 * can be created for invalid pages (for alignment)
> +		 * check here not to call set_pageblock_migratetype() against
> +		 * pfn out of zone.
>  		 */
> -		if ((pfn & (pageblock_nr_pages-1)))
> +		if ((z->zone_start_pfn <= pfn)
> +		    && (pfn < z->zone_start_pfn + z->spanned_pages)
> +		    && !(pfn & (pageblock_nr_pages - 1)))
>  			set_pageblock_migratetype(page, MIGRATE_MOVABLE);
>  

This looks correct. The boundary check is definitly correct and
set_pageblock_migratetype is now only getting called once per pageblock.

>  		INIT_LIST_HEAD(&page->lru);
> @@ -4460,6 +4468,8 @@ void set_pageblock_flags_group(struct pa
>  	pfn = page_to_pfn(page);
>  	bitmap = get_pageblock_bitmap(zone, pfn);
>  	bitidx = pfn_to_bitidx(zone, pfn);
> +	VM_BUG_ON(pfn < zone->zone_start_pfn);
> +	VM_BUG_ON(pfn >= zone->zone_start_pfn + zone->spanned_pages);
>  

Looks good, it would have caught this particular error earlier.

>  	for (; start_bitidx <= end_bitidx; start_bitidx++, value <<= 1)
>  		if (flags & value)
> 

Seems find and boots successfully on a number of machines.

Thanks

Acked-by: Mel Gorman <mel@....ul.ie>

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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