Re: [PATCH 2/8] Fragmentation Avoidance V17: 002_usemap

[Dave Hansen]

On Tue, 2005-10-11 at 16:12 +0100, Mel Gorman wrote: 
> +extern int get_pageblock_type(struct zone *zone,
> +						struct page *page);

That indenting is pretty funky.

> @@ -473,6 +491,15 @@ extern struct pglist_data contig_page_da
>  #if (MAX_ORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS
>  #error Allocator MAX_ORDER exceeds SECTION_SIZE
>  #endif
> +#if ((SECTION_SIZE_BITS - MAX_ORDER) * BITS_PER_RCLM_TYPE) > 64
> +#error free_area_usemap is not big enough
> +#endif

Every time I look at these patches, I see this #if, and I don't remember
what that '64' means.  Can it please get a real name?

> +/* Usemap initialisation */
> +#ifdef CONFIG_SPARSEMEM
> +static inline void setup_usemap(struct pglist_data *pgdat,
> +				struct zone *zone, unsigned long zonesize) {}
> +#endif /* CONFIG_SPARSEMEM */
>  
>  struct page;
>  struct mem_section {
> @@ -485,6 +512,7 @@ struct mem_section {
>  	 * before using it wrong.
>  	 */
>  	unsigned long section_mem_map;
> +	DECLARE_BITMAP(free_area_usemap,64);
>  };

There's that '64' again!  You need a space after the comma, too.

>  #ifdef CONFIG_SPARSEMEM_EXTREME
> @@ -552,6 +580,17 @@ static inline struct mem_section *__pfn_
>  	return __nr_to_section(pfn_to_section_nr(pfn));
>  }
>  
> +static inline unsigned long *pfn_to_usemap(struct zone *zone, unsigned long pfn)
> +{
> +	return &__pfn_to_section(pfn)->free_area_usemap[0];
> +}
> +
> +static inline int pfn_to_bitidx(struct zone *zone, unsigned long pfn)
> +{
> +	pfn &= (PAGES_PER_SECTION-1);
> +	return (int)((pfn >> (MAX_ORDER-1)) * BITS_PER_RCLM_TYPE);
> +}

Why does that return int?  Should it be "unsigned long", maybe?  Also,
that cast is implicit in the return and shouldn't be needed.

>  #define pfn_to_page(pfn) 						\
>  ({ 									\
>  	unsigned long __pfn = (pfn);					\
> @@ -589,6 +628,16 @@ void sparse_init(void);
>  #else
>  #define sparse_init()	do {} while (0)
>  #define sparse_index_init(_sec, _nid)  do {} while (0)
> +static inline unsigned long *pfn_to_usemap(struct zone *zone, 
> +						unsigned long pfn)
> +{
> +	return (zone->free_area_usemap);
> +}

"return" is not a function.  The parenthesis can go away.

> +static inline int pfn_to_bitidx(struct zone *zone, unsigned long pfn)
> +{
> +	pfn = pfn - zone->zone_start_pfn;
> +	return (int)((pfn >> (MAX_ORDER-1)) * BITS_PER_RCLM_TYPE);
> +}

Again, why the cast?

>  #endif /* CONFIG_SPARSEMEM */
>  
>  #ifdef CONFIG_NODES_SPAN_OTHER_NODES
> diff -rup -X /usr/src/patchset-0.5/bin//dontdiff linux-2.6.14-rc3-001_antidefrag_flags/mm/page_alloc.c linux-2.6.14-rc3-002_usemap/mm/page_alloc.c
> --- linux-2.6.14-rc3-001_antidefrag_flags/mm/page_alloc.c	2005-10-04 22:58:34.000000000 +0100
> +++ linux-2.6.14-rc3-002_usemap/mm/page_alloc.c	2005-10-11 12:07:26.000000000 +0100
> @@ -66,6 +66,88 @@ EXPORT_SYMBOL(totalram_pages);
>  EXPORT_SYMBOL(nr_swap_pages);
>  
>  /*
> + * RCLM_SHIFT is the number of bits that a gfp_mask has to be shifted right
> + * to have just the __GFP_USER and __GFP_KERNRCLM bits. The static check is
> + * made afterwards in case the GFP flags are not updated without updating 
> + * this number
> + */
> +#define RCLM_SHIFT 19
> +#if (__GFP_USER >> RCLM_SHIFT) != RCLM_USER
> +#error __GFP_USER not mapping to RCLM_USER
> +#endif
> +#if (__GFP_KERNRCLM >> RCLM_SHIFT) != RCLM_KERN
> +#error __GFP_KERNRCLM not mapping to RCLM_KERN
> +#endif

Should this really be in page_alloc.c, or should it be close to the
RCLM_* definitions?

> +/*
> + * This function maps gfpflags to their RCLM_TYPE. It makes assumptions
> + * on the location of the GFP flags
> + */
> +static inline unsigned long gfpflags_to_rclmtype(unsigned long gfp_flags) {
> +	return (gfp_flags & __GFP_RCLM_BITS) >> RCLM_SHIFT;
> +}

First brace on a new line, please.

> +/*
> + * copy_bits - Copy bits between bitmaps
> + * @dstaddr: The destination bitmap to copy to
> + * @srcaddr: The source bitmap to copy from
> + * @sindex_dst: The start bit index within the destination map to copy to
> + * @sindex_src: The start bit index within the source map to copy from
> + * @nr: The number of bits to copy
> + */
> +static inline void copy_bits(unsigned long *dstaddr,
> +		unsigned long *srcaddr, 
> +		int sindex_dst, 
> +		int sindex_src,
> +		int nr)
> +{
> +	/*
> +	 * Written like this to take advantage of arch-specific 
> +	 * set_bit() and clear_bit() functions
> +	 */
> +	for (nr = nr-1; nr >= 0; nr--) {
> +		int bit = test_bit(sindex_src + nr, srcaddr);
> +		if (bit)
> +			set_bit(sindex_dst + nr, dstaddr);
> +		else
> +			clear_bit(sindex_dst + nr, dstaddr);
> +	}
> +}

We might want to make a note that this is slow, and doesn't have any
atomicity guarantees, either.  But, it's functional, and certainly
describes the operation that we wanted.  It's an improvement over what
was there.

BTW, this could probably be done with some fancy bitmask operations, and
be more efficient.

> +int get_pageblock_type(struct zone *zone,
> +						struct page *page)
> +{
> +	unsigned long pfn = page_to_pfn(page);
> +	unsigned long type = 0;
> +	unsigned long *usemap;
> +	int bitidx;
> +
> +	bitidx = pfn_to_bitidx(zone, pfn);
> +	usemap = pfn_to_usemap(zone, pfn);
> +
> +	copy_bits(&type, usemap, 0, bitidx, BITS_PER_RCLM_TYPE);
> +
> +	return (int)type;
> +}

Where did all these casts come from?

> -static struct page *__rmqueue(struct zone *zone, unsigned int order)
> +static struct page *__rmqueue(struct zone *zone, unsigned int order, 
> +		int alloctype)
>  {
>  	struct free_area * area;
>  	unsigned int current_order;
> @@ -486,6 +569,15 @@ static struct page *__rmqueue(struct zon
>  		rmv_page_order(page);
>  		area->nr_free--;
>  		zone->free_pages -= 1UL << order;
> +
> +		/*
> +		 * If splitting a large block, record what the block is being
> +		 * used for in the usemap
> +		 */
> +		if (current_order == MAX_ORDER-1)
> +			set_pageblock_type(zone, page, 
> +						(unsigned long)alloctype);

This cast makes that line wrap, and makes it quite a bit less readable.

>  		return expand(zone, page, order, current_order, area);
>  	}
>  
> @@ -498,7 +590,8 @@ static struct page *__rmqueue(struct zon
>   * Returns the number of new pages which were placed at *list.
>   */
>  static int rmqueue_bulk(struct zone *zone, unsigned int order, 
> -			unsigned long count, struct list_head *list)
> +			unsigned long count, struct list_head *list,
> +			int alloctype)
>  {
>  	unsigned long flags;
>  	int i;
> @@ -507,7 +600,7 @@ static int rmqueue_bulk(struct zone *zon
>  	
>  	spin_lock_irqsave(&zone->lock, flags);
>  	for (i = 0; i < count; ++i) {
> -		page = __rmqueue(zone, order);
> +		page = __rmqueue(zone, order, alloctype);
>  		if (page == NULL)
>  			break;
>  		allocated++;
> @@ -691,7 +784,8 @@ buffered_rmqueue(struct zone *zone, int 
>  	unsigned long flags;
>  	struct page *page = NULL;
>  	int cold = !!(gfp_flags & __GFP_COLD);
> -
> +	int alloctype = (int)gfpflags_to_rclmtype(gfp_flags);
> +	

Just a note: that inserts whitespace.

You can avoid these kinds of mistakes by keeping incremental patches.
Start with your last set of work, and keep all changes to _that_ work in
separate patches on top of the old.  You'll see only what you change and
little tiny mishaps like this will tend to jump out more than in the
hundreds of lines of the whole thing.

-- Dave

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