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Date: Thu, 21 Mar 2013 18:13:56 +0000
From: Mel Gorman <mgorman@...e.de>
To: Michal Hocko <mhocko@...e.cz>
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 Thu, Mar 21, 2013 at 06:18:04PM +0100, Michal Hocko wrote:
> On Sun 17-03-13 13:04:16, Mel Gorman wrote:
> > +
> > + /*
> > + * 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
>
It would.
> > + 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.
>
True, it only makes sense to account for the pages it actually attempted
to reclaim. Thanks.
--
Mel Gorman
SUSE Labs
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