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    Subject[PATCH v2 -mm 1/3] mm: reclaim at order 0 when compaction is enabled
    When built with CONFIG_COMPACTION, kswapd does not try to free
    contiguous pages. Because it is not trying, it should also not
    test whether it succeeded, because that can result in continuous
    page reclaim, until a large fraction of memory is free and large
    fractions of the working set have been evicted.

    In shrink_inactive_list, we should not try to do higher order
    (out of LRU order) page isolation, unless we really are in
    lumpy reclaim mode. This gives all pages a good amount of time
    on the inactive list, giving the actively used pages the chance
    to get referenced and avoid eviction.

    Also remove a line of code that increments balanced right before
    exiting the function.

    Signed-off-by: Rik van Riel <riel@redhat.com>
    ---
    mm/vmscan.c | 29 ++++++++++++++++++++++-------
    1 files changed, 22 insertions(+), 7 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 2880396..0398fab 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -1512,6 +1512,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct mem_cgroup_zone *mz,
    unsigned long nr_writeback = 0;
    isolate_mode_t reclaim_mode = ISOLATE_INACTIVE;
    struct zone *zone = mz->zone;
    + int order = 0;

    while (unlikely(too_many_isolated(zone, file, sc))) {
    congestion_wait(BLK_RW_ASYNC, HZ/10);
    @@ -1522,8 +1523,10 @@ shrink_inactive_list(unsigned long nr_to_scan, struct mem_cgroup_zone *mz,
    }

    set_reclaim_mode(priority, sc, false);
    - if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
    + if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM) {
    reclaim_mode |= ISOLATE_ACTIVE;
    + order = sc->order;
    + }

    lru_add_drain();

    @@ -1535,7 +1538,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct mem_cgroup_zone *mz,
    spin_lock_irq(&zone->lru_lock);

    nr_taken = isolate_lru_pages(nr_to_scan, mz, &page_list,
    - &nr_scanned, sc->order,
    + &nr_scanned, order,
    reclaim_mode, 0, file);
    if (global_reclaim(sc)) {
    zone->pages_scanned += nr_scanned;
    @@ -2754,7 +2757,7 @@ loop_again:
    */
    for (i = 0; i <= end_zone; i++) {
    struct zone *zone = pgdat->node_zones + i;
    - int nr_slab;
    + int nr_slab, testorder;
    unsigned long balance_gap;

    if (!populated_zone(zone))
    @@ -2783,11 +2786,25 @@ loop_again:
    * gap is either the low watermark or 1%
    * of the zone, whichever is smaller.
    */
    + testorder = order;
    balance_gap = min(low_wmark_pages(zone),
    (zone->present_pages +
    KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
    KSWAPD_ZONE_BALANCE_GAP_RATIO);
    - if (!zone_watermark_ok_safe(zone, order,
    + /*
    + * Kswapd reclaims only single pages when
    + * COMPACTION_BUILD. Trying too hard to get
    + * contiguous free pages can result in excessive
    + * amounts of free memory, and useful things
    + * getting kicked out of memory.
    + * Limit the amount of reclaim to something sane,
    + * plus space for compaction to do its thing.
    + */
    + if (COMPACTION_BUILD) {
    + testorder = 0;
    + balance_gap += 2<<order;
    + }
    + if (!zone_watermark_ok_safe(zone, testorder,
    high_wmark_pages(zone) + balance_gap,
    end_zone, 0)) {
    shrink_zone(priority, zone, &sc);
    @@ -2816,7 +2833,7 @@ loop_again:
    continue;
    }

    - if (!zone_watermark_ok_safe(zone, order,
    + if (!zone_watermark_ok_safe(zone, testorder,
    high_wmark_pages(zone), end_zone, 0)) {
    all_zones_ok = 0;
    /*
    @@ -2922,8 +2939,6 @@ out:

    /* If balanced, clear the congested flag */
    zone_clear_flag(zone, ZONE_CONGESTED);
    - if (i <= *classzone_idx)
    - balanced += zone->present_pages;
    }
    }

    .

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