lkml.org 
[lkml]   [2012]   [Dec]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] mm: Use aligned zone start for pfn_to_bitidx calculation
On 12/6/2012 12:05 PM, Laura Abbott wrote:
> The current calculation in pfn_to_bitidx assumes that
> (pfn - zone->zone_start_pfn) >> pageblock_order will return the
> same bit for all pfn in a pageblock. If zone_start_pfn is not
> aligned to pageblock_nr_pages, this may not always be correct.
>
> Consider the following with pageblock order = 10, zone start 2MB:
>
> pfn | pfn - zone start | (pfn - zone start) >> page block order
> ----------------------------------------------------------------
> 0x26000 | 0x25e00 | 0x97
> 0x26100 | 0x25f00 | 0x97
> 0x26200 | 0x26000 | 0x98
> 0x26300 | 0x26100 | 0x98
>
> This means that calling {get,set}_pageblock_migratetype on a single
> page will not set the migratetype for the full block. Fix this by
> rounding down zone_start_pfn when doing the bitidx calculation.
>
> Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
> ---
> mm/page_alloc.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 92dd060..2e06abd 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5422,7 +5422,7 @@ static inline int pfn_to_bitidx(struct zone *zone, unsigned long pfn)
> pfn &= (PAGES_PER_SECTION-1);
> return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
> #else
> - pfn = pfn - zone->zone_start_pfn;
> + pfn = pfn - round_down(zone->start_pfn, pageblock_nr_pages);
> return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
> #endif /* CONFIG_SPARSEMEM */
> }
>

Sorry for the spam, please ignore this one. This has a typo. Third times
the charm.

--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation


\
 
 \ /
  Last update: 2012-12-06 23:01    [W:0.023 / U:0.136 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site