mm: vmscan: fix endless loop in kswapd balancing (60cefed4) · Commits · 戴 / test

Kswapd does not in all places have the same criteria for a balanced zone. Zones are only being reclaimed when their high watermark is breached, but compaction checks loop over the zonelist again when the zone does not meet the low watermark plus two times the size of the allocation. This gets kswapd stuck in an endless loop over a small zone, like the DMA zone, where the high watermark is smaller than the compaction requirement. Add a function, zone_balanced(), that checks the watermark, and, for higher order allocations, if compaction has enough free memory. Then use it uniformly to check for balanced zones. This makes sure that when the compaction watermark is not met, at least reclaim happens and progress is made - or the zone is declared unreclaimable at some point and skipped entirely. Signed-off-by:

Johannes Weiner <hannes@cmpxchg.org> Reported-by:

George Spelvin <linux@horizon.com> Reported-by:

Johannes Hirte <johannes.hirte@fem.tu-ilmenau.de> Reported-by:

Tomas Racek <tracek@redhat.com> Tested-by:

Johannes Hirte <johannes.hirte@fem.tu-ilmenau.de> Reviewed-by:

Rik van Riel <riel@redhat.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: <stable@vger.kernel.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

+18 −9

Original line number	Diff line number	Diff line
		@@ -2414,6 +2414,19 @@ static void age_active_anon(struct zone zone, struct scan_control sc)
		} while (memcg);
		}

		static bool zone_balanced(struct zone *zone, int order,
		unsigned long balance_gap, int classzone_idx)
		{
		if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
		balance_gap, classzone_idx, 0))
		return false;

		if (COMPACTION_BUILD && order && !compaction_suitable(zone, order))
		return false;

		return true;
		}

		/*
		* pgdat_balanced is used when checking if a node is balanced for high-order
		* allocations. Only zones that meet watermarks and are in a zone allowed
		@@ -2492,8 +2505,7 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
		continue;
		}

		if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
		i, 0))
		if (!zone_balanced(zone, order, 0, i))
		all_zones_ok = false;
		else
		balanced += zone->present_pages;
		@@ -2602,8 +2614,7 @@ loop_again:
		break;
		}

		if (!zone_watermark_ok_safe(zone, order,
		high_wmark_pages(zone), 0, 0)) {
		if (!zone_balanced(zone, order, 0, 0)) {
		end_zone = i;
		break;
		} else {
		@@ -2679,9 +2690,8 @@ loop_again:
		testorder = 0;

		if ((buffer_heads_over_limit && is_highmem_idx(i)) \|\|
		!zone_watermark_ok_safe(zone, testorder,
		high_wmark_pages(zone) + balance_gap,
		end_zone, 0)) {
		!zone_balanced(zone, testorder,
		balance_gap, end_zone)) {
		shrink_zone(zone, &sc);

		reclaim_state->reclaimed_slab = 0;
		@@ -2708,8 +2718,7 @@ loop_again:
		continue;
		}

		if (!zone_watermark_ok_safe(zone, testorder,
		high_wmark_pages(zone), end_zone, 0)) {
		if (!zone_balanced(zone, testorder, 0, end_zone)) {
		all_zones_ok = 0;
		/*
		* We are still under min water mark. This

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