[PATCH] mm: Check if any page in a pageblock is reserved before marking it MIGRATE_RESERVE

[Mel Gorman]

On Mon, Apr 05, 2010 at 08:09:16PM -0700, Arve Hj?nnev?g wrote:
> This fixes a problem where the first pageblock got marked MIGRATE_RESERVE even
> though it only had a few free pages. This in turn caused no contiguous memory
> to be reserved and frequent kswapd wakeups that emptied the caches to get more
> contiguous memory.
> 
> Signed-off-by: Arve Hjønnevåg <arve at android.com>

I would have used pageblock_reserve_suitable because what you are really
checking is "is this page block suitable for use by MIGRATE_RESERVE?".
The definition was "is the first page PageReserved" and you are changing it to
"does the page block have any memory holes or PageReserved pages?"

No biggie though. Change it if you like before upstreaming. Either way.

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


Thanks

> ---
>  mm/page_alloc.c |   16 +++++++++++++++-
>  1 files changed, 15 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index fb7df1d..46ade16 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2860,6 +2860,20 @@ static inline unsigned long wait_table_bits(unsigned long size)
>  #define LONG_ALIGN(x) (((x)+(sizeof(long))-1)&~((sizeof(long))-1))
>  
>  /*
> + * Check if a pageblock contains reserved pages
> + */
> +static int pageblock_is_reserved(unsigned long start_pfn)
> +{
> +	unsigned long end_pfn = start_pfn + pageblock_nr_pages;
> +	unsigned long pfn;
> +
> +	for (pfn = start_pfn; pfn < end_pfn; pfn++)
> +		if (!pfn_valid_within(pfn) || PageReserved(pfn_to_page(pfn)))
> +			return 1;
> +	return 0;
> +}
> +
> +/*
>   * Mark a number of pageblocks as MIGRATE_RESERVE. The number
>   * of blocks reserved is based on min_wmark_pages(zone). The memory within
>   * the reserve will tend to store contiguous free pages. Setting min_free_kbytes
> @@ -2898,7 +2912,7 @@ static void setup_zone_migrate_reserve(struct zone *zone)
>  			continue;
>  
>  		/* Blocks with reserved pages will never free, skip them. */
> -		if (PageReserved(page))
> +		if (pageblock_is_reserved(pfn))
>  			continue;
>  
>  		block_migratetype = get_pageblock_migratetype(page);
> -- 
> 1.6.5.1
> 

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