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Date: Thu, 21 Mar 2013 18:18:04 +0100
From: Michal Hocko <mhocko@...e.cz>
To: Mel Gorman <mgorman@...e.de>
Cc: Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz>,
Valdis Kletnieks <Valdis.Kletnieks@...edu>,
Rik van Riel <riel@...hat.com>,
Zlatko Calusic <zcalusic@...sync.net>,
Johannes Weiner <hannes@...xchg.org>,
dormando <dormando@...ia.net>,
Satoru Moriya <satoru.moriya@....com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/10] mm: vmscan: Move logic from balance_pgdat() to
kswapd_shrink_zone()
On Sun 17-03-13 13:04:16, Mel Gorman wrote:
> 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@...e.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)))
if (!lowmem_pressure && zone_balanced) would be less cryptic I guess
> + 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;
> }
nr_to_reclaim is updated if the zone is balanced an no reclaim is done
which break compaction condition AFAICS.
--
Michal Hocko
SUSE Labs
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