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From: Vlastimil Babka <vbabka@suse.cz>
To: Mel Gorman <mgorman@techsingularity.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux-MM <linux-mm@kvack.org>
Cc: Rik van Riel <riel@surriel.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 06/27] mm, vmscan: Make kswapd reclaim in terms of nodes
Date: Thu, 28 Apr 2016 10:36:35 +0200	[thread overview]
Message-ID: <5721CB93.8000207@suse.cz> (raw)
In-Reply-To: <1460711613-2761-7-git-send-email-mgorman@techsingularity.net>

On 04/15/2016 11:13 AM, Mel Gorman wrote:
>   	/*
> -	 * 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.
> +	 * Fragmentation may mean that the system cannot be rebalanced for
> +	 * high-order allocations. If twice the allocation size has been
> +	 * reclaimed then recheck watermarks only at order-0 to prevent
> +	 * excessive reclaim. Assume that a process requested a high-order
> +	 * can direct reclaim/compact.

Also kcompactd is woken up in this case...

>   	 */
> -	if (pgdat_reclaimable(zone->zone_pgdat) &&
> -	    zone_balanced(zone, sc->order, false, 0, classzone_idx)) {
> -		clear_bit(PGDAT_CONGESTED, &pgdat->flags);
> -		clear_bit(PGDAT_DIRTY, &pgdat->flags);
> -	}
> +	if (sc->order && sc->nr_reclaimed >= 2UL << sc->order)
> +		sc->order = 0;
>
>   	return sc->nr_scanned >= sc->nr_to_reclaim;

This looks indeed simpler than my earlier zone_balanced() modification 
you removed. However I think there's still potential of overreclaim due 
to a stream of kswapd_wakeups where each will have to reclaim 2UL << 
sc->order pages, regardless of watermarks. Could be some high-order 
wakeups from GFP_ATOMIC context that have order-0 fallbacks but will 
cause kswapd to keep reclaiming when kcompactd can't keep up due to 
fragmentation...

  reply	other threads:[~2016-04-28  8:36 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-15  9:13 [PATCH 00/27] Move LRU page reclaim from zones to nodes v5 Mel Gorman
2016-04-15  9:13 ` [PATCH 01/27] mm, vmstat: Add infrastructure for per-node vmstats Mel Gorman
2016-04-15  9:13 ` [PATCH 02/27] mm, vmscan: Move lru_lock to the node Mel Gorman
2016-04-15  9:13 ` [PATCH 03/27] mm, vmscan: Move LRU lists to node Mel Gorman
2016-04-15  9:13 ` [PATCH 04/27] mm, vmscan: Begin reclaiming pages on a per-node basis Mel Gorman
2016-04-15  9:13 ` [PATCH 05/27] mm, vmscan: Have kswapd only scan based on the highest requested zone Mel Gorman
2016-04-15  9:13 ` [PATCH 06/27] mm, vmscan: Make kswapd reclaim in terms of nodes Mel Gorman
2016-04-28  8:36   ` Vlastimil Babka [this message]
2016-04-15  9:13 ` [PATCH 07/27] mm, vmscan: Remove balance gap Mel Gorman
2016-04-15  9:13 ` [PATCH 08/27] mm, vmscan: Simplify the logic deciding whether kswapd sleeps Mel Gorman
2016-04-15  9:13 ` [PATCH 09/27] mm, vmscan: By default have direct reclaim only shrink once per node Mel Gorman
2016-04-15  9:13 ` [PATCH 10/27] mm, vmscan: Clear congestion, dirty and need for compaction on a per-node basis Mel Gorman
2016-04-15  9:13 ` [PATCH 11/27] mm: vmscan: Do not reclaim from kswapd if there is any eligible zone Mel Gorman
2016-04-15  9:13 ` [PATCH 12/27] mm, vmscan: Make shrink_node decisions more node-centric Mel Gorman
2016-04-15  9:13 ` [PATCH 13/27] mm, memcg: Move memcg limit enforcement from zones to nodes Mel Gorman
2016-04-15  9:13 ` [PATCH 14/27] mm, workingset: Make working set detection node-aware Mel Gorman
2016-04-15  9:13 ` [PATCH 15/27] mm, page_alloc: Consider dirtyable memory in terms of nodes Mel Gorman
2016-04-15  9:13 ` [PATCH 16/27] mm: Move page mapped accounting to the node Mel Gorman
2016-04-15  9:13 ` [PATCH 17/27] mm: Rename NR_ANON_PAGES to NR_ANON_MAPPED Mel Gorman
2016-04-15  9:13 ` [PATCH 18/27] mm: Move most file-based accounting to the node Mel Gorman
2016-04-15  9:13 ` [PATCH 19/27] mm: Move vmscan writes and file write " Mel Gorman
2016-04-15  9:13 ` [PATCH 20/27] mm, vmscan: Update classzone_idx if buffer_heads_over_limit Mel Gorman
2016-04-15  9:13 ` [PATCH 21/27] mm, vmscan: Only wakeup kswapd once per node for the requested classzone Mel Gorman
2016-04-15  9:13 ` [PATCH 22/27] mm: Convert zone_reclaim to node_reclaim Mel Gorman
2016-04-15  9:13 ` [PATCH 23/27] mm, vmscan: Add classzone information to tracepoints Mel Gorman
2016-04-15  9:13 ` [PATCH 24/27] mm, page_alloc: Remove fair zone allocation policy Mel Gorman
2016-04-15  9:13 ` [PATCH 25/27] mm: page_alloc: Cache the last node whose dirty limit is reached Mel Gorman
2016-04-15  9:13 ` [PATCH 26/27] mm: vmstat: Replace __count_zone_vm_events with a zone id equivalent Mel Gorman
2016-04-15  9:13 ` [PATCH 27/27] mm: vmstat: Account per-zone stalls and pages skipped during reclaim Mel Gorman
2016-06-09 18:04 [PATCH 00/27] Move LRU page reclaim from zones to nodes v6 Mel Gorman
2016-06-09 18:04 ` [PATCH 06/27] mm, vmscan: Make kswapd reclaim in terms of nodes Mel Gorman
2016-06-15 14:23   ` Vlastimil Babka
     [not found] <02fe01d1c48b$c44e9e80$4cebdb80$@alibaba-inc.com>
2016-06-12  9:33 ` Hillf Danton
2016-06-14 14:52   ` Mel Gorman
2016-06-21 14:15 [PATCH 00/27] Move LRU page reclaim from zones to nodes v7 Mel Gorman
2016-06-21 14:15 ` [PATCH 06/27] mm, vmscan: Make kswapd reclaim in terms of nodes Mel Gorman
     [not found] <071801d1cc5c$245087d0$6cf19770$@alibaba-inc.com>
2016-06-22  8:42 ` Hillf Danton
2016-06-23 11:31   ` Mel Gorman

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