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    Subject[RFC PATCH v4 39/40] mm: Add intelligence in kmempowerd to ignore regions unsuitable for evacuation
    Date
    Enhance kmempowerd to determine situations where evacuating a region would prove
    to be too costly or counter-productive, and ignore those regions for region
    evacuation.

    For example, if the region has a significant number of used pages (say more than
    32), then evacuation will involve more work and might not be justifiable. Also,
    compacting region 0 would be pointless, since that is the target of all our
    compaction runs. Add these checks in the region-evacuator.

    Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    ---

    include/linux/mmzone.h | 2 ++
    mm/compaction.c | 25 +++++++++++++++++++++++--
    mm/internal.h | 2 ++
    3 files changed, 27 insertions(+), 2 deletions(-)

    diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
    index 257afdf..f383cc8d4 100644
    --- a/include/linux/mmzone.h
    +++ b/include/linux/mmzone.h
    @@ -84,6 +84,8 @@ static inline int get_pageblock_migratetype(struct page *page)
    return get_pageblock_flags_group(page, PB_migrate, PB_migrate_end);
    }

    +#define MAX_MEMPWR_MIGRATE_PAGES 32
    +
    struct mem_region_list {
    struct list_head *page_block;
    unsigned long nr_free;
    diff --git a/mm/compaction.c b/mm/compaction.c
    index b56be89..41585b0 100644
    --- a/mm/compaction.c
    +++ b/mm/compaction.c
    @@ -1297,9 +1297,26 @@ void queue_mempower_work(struct pglist_data *pgdat, struct zone *zone,
    queue_kthread_work(&pgdat->mempower_worker, &mpwork->work);
    }

    +int should_evacuate_region(struct zone *z, struct zone_mem_region *region)
    +{
    + unsigned long pages_in_use;
    +
    + /* Don't try to evacuate region 0, since its the target of migration */
    + if (region == z->zone_regions)
    + return 0;
    +
    + pages_in_use = region->present_pages - region->nr_free;
    +
    + if (pages_in_use > 0 && pages_in_use <= MAX_MEMPWR_MIGRATE_PAGES)
    + return 1;
    +
    + return 0;
    +}
    +
    static void kmempowerd(struct kthread_work *work)
    {
    struct mempower_work *mpwork;
    + struct zone_mem_region *zmr;
    struct zone *zone;
    unsigned long flags;
    int region_id;
    @@ -1315,8 +1332,12 @@ repeat:
    if (bitmap_empty(mpwork_mask, nr_zone_region_bits))
    return;

    - for_each_set_bit(region_id, mpwork_mask, nr_zone_region_bits)
    - evacuate_mem_region(zone, &zone->zone_regions[region_id]);
    + for_each_set_bit(region_id, mpwork_mask, nr_zone_region_bits) {
    + zmr = &zone->zone_regions[region_id];
    +
    + if (should_evacuate_region(zone, zmr))
    + evacuate_mem_region(zone, zmr);
    + }

    spin_lock_irqsave(&mpwork->lock, flags);

    diff --git a/mm/internal.h b/mm/internal.h
    index 3fbc9f6..5b4658c 100644
    --- a/mm/internal.h
    +++ b/mm/internal.h
    @@ -184,6 +184,8 @@ int compact_range(struct compact_control *cc, struct aggression_control *ac,
    void queue_mempower_work(struct pglist_data *pgdat, struct zone *zone,
    int region_id);

    +int should_evacuate_region(struct zone *z, struct zone_mem_region *region);
    +
    #endif

    /*


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