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    SubjectRe: [PATCH 08/10] mm: vmscan: Have kswapd shrink slab only once per priority
    On Sun 17-03-13 13:04:14, Mel Gorman wrote:
    > If kswaps fails to make progress but continues to shrink slab then it'll
    > either discard all of slab or consume CPU uselessly scanning shrinkers.
    > This patch causes kswapd to only call the shrinkers once per priority.
    >
    > Signed-off-by: Mel Gorman <mgorman@suse.de>

    OK, looks good.
    Reviewed-by: Michal Hocko <mhocko@suse.cz>

    > ---
    > mm/vmscan.c | 28 +++++++++++++++++++++-------
    > 1 file changed, 21 insertions(+), 7 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index 7d5a932..84375b2 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -2661,9 +2661,10 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
    > */
    > static bool kswapd_shrink_zone(struct zone *zone,
    > struct scan_control *sc,
    > - unsigned long lru_pages)
    > + unsigned long lru_pages,
    > + bool shrinking_slab)
    > {
    > - unsigned long nr_slab;
    > + unsigned long nr_slab = 0;
    > struct reclaim_state *reclaim_state = current->reclaim_state;
    > struct shrink_control shrink = {
    > .gfp_mask = sc->gfp_mask,
    > @@ -2673,9 +2674,15 @@ static bool kswapd_shrink_zone(struct zone *zone,
    > sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
    > shrink_zone(zone, sc);
    >
    > - reclaim_state->reclaimed_slab = 0;
    > - nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages);
    > - sc->nr_reclaimed += reclaim_state->reclaimed_slab;
    > + /*
    > + * Slabs are shrunk for each zone once per priority or if the zone
    > + * being balanced is otherwise unreclaimable
    > + */
    > + if (shrinking_slab || !zone_reclaimable(zone)) {
    > + reclaim_state->reclaimed_slab = 0;
    > + nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages);
    > + sc->nr_reclaimed += reclaim_state->reclaimed_slab;
    > + }
    >
    > if (nr_slab == 0 && !zone_reclaimable(zone))
    > zone->all_unreclaimable = 1;
    > @@ -2713,6 +2720,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    > int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
    > unsigned long nr_soft_reclaimed;
    > unsigned long nr_soft_scanned;
    > + bool shrinking_slab = true;
    > struct scan_control sc = {
    > .gfp_mask = GFP_KERNEL,
    > .priority = DEF_PRIORITY,
    > @@ -2861,7 +2869,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    > * already being scanned that that high
    > * watermark would be met at 100% efficiency.
    > */
    > - if (kswapd_shrink_zone(zone, &sc, lru_pages))
    > + if (kswapd_shrink_zone(zone, &sc,
    > + lru_pages, shrinking_slab))
    > raise_priority = false;
    >
    > nr_to_reclaim += sc.nr_to_reclaim;
    > @@ -2900,6 +2909,9 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    > pfmemalloc_watermark_ok(pgdat))
    > wake_up(&pgdat->pfmemalloc_wait);
    >
    > + /* Only shrink slab once per priority */
    > + shrinking_slab = false;
    > +
    > /*
    > * Fragmentation may mean that the system cannot be rebalanced
    > * for high-order allocations in all zones. If twice the
    > @@ -2925,8 +2937,10 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    > * Raise priority if scanning rate is too low or there was no
    > * progress in reclaiming pages
    > */
    > - if (raise_priority || !this_reclaimed)
    > + if (raise_priority || !this_reclaimed) {
    > sc.priority--;
    > + shrinking_slab = true;
    > + }
    > } while (sc.priority >= 1 &&
    > !pgdat_balanced(pgdat, order, *classzone_idx));
    >
    > --
    > 1.8.1.4
    >

    --
    Michal Hocko
    SUSE Labs


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