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    Subject[PATCH 10/10] mm: vmscan: Move logic from balance_pgdat() to kswapd_shrink_zone()
    Date
    balance_pgdat() is very long and some of the logic can and should
    be internal to kswapd_shrink_zone(). Move it so the flow of
    balance_pgdat() is marginally easier to follow.

    Signed-off-by: Mel Gorman <mgorman@suse.de>
    ---
    mm/vmscan.c | 104 +++++++++++++++++++++++++++++-------------------------------
    1 file changed, 51 insertions(+), 53 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 8c66e5a..d7cf384 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -2660,18 +2660,53 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
    * reclaim or if the lack of process was due to pages under writeback.
    */
    static bool kswapd_shrink_zone(struct zone *zone,
    + int classzone_idx,
    struct scan_control *sc,
    unsigned long lru_pages,
    bool shrinking_slab)
    {
    + int testorder = sc->order;
    unsigned long nr_slab = 0;
    + unsigned long balance_gap;
    struct reclaim_state *reclaim_state = current->reclaim_state;
    struct shrink_control shrink = {
    .gfp_mask = sc->gfp_mask,
    };
    + bool lowmem_pressure;

    /* Reclaim above the high watermark. */
    sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
    +
    + /*
    + * Kswapd reclaims only single pages with compaction enabled. Trying
    + * too hard to reclaim until contiguous free pages have become
    + * available can hurt performance by evicting too much useful data
    + * from memory. Do not reclaim more than needed for compaction.
    + */
    + if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
    + compaction_suitable(zone, sc->order) !=
    + COMPACT_SKIPPED)
    + testorder = 0;
    +
    + /*
    + * We put equal pressure on every zone, unless one zone has way too
    + * many pages free already. The "too many pages" is defined as the
    + * high wmark plus a "gap" where the gap is either the low
    + * watermark or 1% of the zone, whichever is smaller.
    + */
    + balance_gap = min(low_wmark_pages(zone),
    + (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
    + KSWAPD_ZONE_BALANCE_GAP_RATIO);
    +
    + /*
    + * If there is no low memory pressure or the zone is balanced then no
    + * reclaim is necessary
    + */
    + lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
    + if (!(lowmem_pressure || !zone_balanced(zone, testorder,
    + balance_gap, classzone_idx)))
    + return true;
    +
    shrink_zone(zone, sc);

    /*
    @@ -2689,6 +2724,16 @@ static bool kswapd_shrink_zone(struct zone *zone,

    zone_clear_flag(zone, ZONE_WRITEBACK);

    + /*
    + * If a zone reaches its high watermark, consider it to be no longer
    + * congested. It's possible there are dirty pages backed by congested
    + * BDIs but as pressure is relieved, speculatively avoid congestion
    + * waits.
    + */
    + if (!zone->all_unreclaimable &&
    + zone_balanced(zone, testorder, 0, classzone_idx))
    + zone_clear_flag(zone, ZONE_CONGESTED);
    +
    return sc->nr_scanned >= sc->nr_to_reclaim;
    }

    @@ -2821,8 +2866,6 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    */
    for (i = 0; i <= end_zone; i++) {
    struct zone *zone = pgdat->node_zones + i;
    - int testorder;
    - unsigned long balance_gap;

    if (!populated_zone(zone))
    continue;
    @@ -2843,61 +2886,16 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    sc.nr_reclaimed += nr_soft_reclaimed;

    /*
    - * We put equal pressure on every zone, unless
    - * one zone has way too many pages free
    - * already. The "too many pages" is defined
    - * as the high wmark plus a "gap" where the
    - * gap is either the low watermark or 1%
    - * of the zone, whichever is smaller.
    - */
    - balance_gap = min(low_wmark_pages(zone),
    - (zone->managed_pages +
    - KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
    - KSWAPD_ZONE_BALANCE_GAP_RATIO);
    - /*
    - * Kswapd reclaims only single pages with compaction
    - * enabled. Trying too hard to reclaim until contiguous
    - * free pages have become available can hurt performance
    - * by evicting too much useful data from memory.
    - * Do not reclaim more than needed for compaction.
    + * There should be no need to raise the scanning
    + * priority if enough pages are already being scanned
    + * that that high watermark would be met at 100%
    + * efficiency.
    */
    - testorder = order;
    - if (IS_ENABLED(CONFIG_COMPACTION) && order &&
    - compaction_suitable(zone, order) !=
    - COMPACT_SKIPPED)
    - testorder = 0;
    -
    - if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
    - !zone_balanced(zone, testorder,
    - balance_gap, end_zone)) {
    - /*
    - * There should be no need to raise the
    - * scanning priority if enough pages are
    - * already being scanned that that high
    - * watermark would be met at 100% efficiency.
    - */
    - if (kswapd_shrink_zone(zone, &sc,
    + if (kswapd_shrink_zone(zone, end_zone, &sc,
    lru_pages, shrinking_slab))
    raise_priority = false;

    - nr_to_reclaim += sc.nr_to_reclaim;
    - }
    -
    - if (zone->all_unreclaimable) {
    - if (end_zone && end_zone == i)
    - end_zone--;
    - continue;
    - }
    -
    - if (zone_balanced(zone, testorder, 0, end_zone))
    - /*
    - * If a zone reaches its high watermark,
    - * consider it to be no longer congested. It's
    - * possible there are dirty pages backed by
    - * congested BDIs but as pressure is relieved,
    - * speculatively avoid congestion waits
    - */
    - zone_clear_flag(zone, ZONE_CONGESTED);
    + nr_to_reclaim += sc.nr_to_reclaim;
    }

    /*
    --
    1.8.1.4


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