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    Subject[PATCH] mm: Check if any page in a pageblock is reserved before marking it MIGRATE_RESERVE
    Date
    From: Arve Hjønnevåg <arve@android.com>

    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.

    CC: Dave Hansen <dave@linux.vnet.ibm.com>
    CC: Mel Gorman <mgorman@suse.de>
    CC: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Arve Hjønnevåg <arve@android.com>
    Acked-by: Mel Gorman <mel@csn.ul.ie>

    [This patch was submitted and acked a little over a year ago
    (see: http://lkml.org/lkml/2010/4/6/172 ), but never seemingly
    made it upstream. Resending for comments. -jstultz]

    Signed-off-by: John Stultz <john.stultz@linaro.org>
    ---
    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 ed87f3b..209d9bf 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -3288,6 +3288,20 @@ 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 (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
    @@ -3326,7 +3340,7 @@ 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);
    --
    1.7.3.2.146.gca209
    --
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