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From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Linux-MM <linux-mm@kvack.org>, Rik van Riel <riel@surriel.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 08/27] mm, vmscan: Simplify the logic deciding whether kswapd sleeps
Date: Thu, 16 Jun 2016 09:30:33 +0100	[thread overview]
Message-ID: <20160616083033.GF1868@techsingularity.net> (raw)
In-Reply-To: <6b6b9f95-869a-a9f2-c5cf-f0a3e4d6bd6a@suse.cz>

On Wed, Jun 15, 2016 at 05:18:00PM +0200, Vlastimil Babka wrote:
> >@@ -1209,9 +1209,10 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
> >
> > 		arch_refresh_nodedata(nid, pgdat);
> > 	} else {
> >-		/* Reset the nr_zones and classzone_idx to 0 before reuse */
> >+		/* Reset the nr_zones, order and classzone_idx before reuse */
> > 		pgdat->nr_zones = 0;
> >-		pgdat->classzone_idx = 0;
> >+		pgdat->kswapd_order = 0;
> >+		pgdat->kswapd_classzone_idx = -1;
> > 	}
> >
> > 	/* we can use NODE_DATA(nid) from here */
> >diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >index 4ce578b969da..d8cb483d5cad 100644
> >--- a/mm/page_alloc.c
> >+++ b/mm/page_alloc.c
> >@@ -6036,7 +6036,7 @@ void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
> > 	unsigned long end_pfn = 0;
> >
> > 	/* pg_data_t should be reset to zero when it's allocated */
> >-	WARN_ON(pgdat->nr_zones || pgdat->classzone_idx);
> >+	WARN_ON(pgdat->nr_zones || pgdat->kswapd_classzone_idx);
> 
> Above you changed the reset value of kswapd_classzone_idx from 0 to -1, so
> won't this trigger? Also should we check kswapd_order that's newly reset
> too?
> 

Good spot. The memory initialisation paths are ok but node memory hotplug
was broken.

> >
> > 	reset_deferred_meminit(pgdat);
> > 	pgdat->node_id = nid;
> >diff --git a/mm/vmscan.c b/mm/vmscan.c
> >index 96bf841f9352..14b34eebedff 100644
> >--- a/mm/vmscan.c
> >+++ b/mm/vmscan.c
> >@@ -2727,7 +2727,7 @@ static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
> >
> > 	/* kswapd must be awake if processes are being throttled */
> > 	if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
> >-		pgdat->classzone_idx = min(pgdat->classzone_idx,
> >+		pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
> > 						(enum zone_type)ZONE_NORMAL);
> > 		wake_up_interruptible(&pgdat->kswapd_wait);
> > 	}
> >@@ -3211,6 +3211,12 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order,
> >
> > 	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
> >
> >+	/* If kswapd has not been woken recently, then full sleep */
> >+	if (classzone_idx == -1) {
> >+		classzone_idx = balanced_classzone_idx = MAX_NR_ZONES - 1;
> >+		goto full_sleep;
> 
> This will skip the wakeup_kcompactd() part.
> 

I wrestled with this one. I decided to leave it alone on the grounds
that if kswapd has not been woken recently then compaction efforts also
have not failed and kcompactd is not required.

> >@@ -3311,38 +3316,25 @@ static int kswapd(void *p)
> > 	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
> > 	set_freezable();
> >
> >-	order = new_order = 0;
> >-	classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
> >-	balanced_classzone_idx = classzone_idx;
> >+	pgdat->kswapd_order = order = 0;
> >+	pgdat->kswapd_classzone_idx = classzone_idx = -1;
> > 	for ( ; ; ) {
> > 		bool ret;
> >
> >+kswapd_try_sleep:
> >+		kswapd_try_to_sleep(pgdat, order, classzone_idx, classzone_idx);
> 
> The last two parameters are now the same, remove one?
> 

Yes. A few more basic simplifications are then possible.

> >@@ -3352,12 +3344,19 @@ static int kswapd(void *p)
> > 		 * We can speed up thawing tasks if we don't call balance_pgdat
> > 		 * after returning from the refrigerator
> > 		 */
> >-		if (!ret) {
> >-			trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
> >+		if (ret)
> >+			continue;
> >
> >-			/* return value ignored until next patch */
> >-			balance_pgdat(pgdat, order, classzone_idx);
> >-		}
> >+		/*
> >+		 * Try reclaim the requested order but if that fails
> >+		 * then try sleeping on the basis of the order reclaimed.
> 
> Is the last word really meant to be "reclaimed", or "requested"?
> 

No, I really meant reclaimed.

> >+		 */
> >+		trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
> >+		if (balance_pgdat(pgdat, order, classzone_idx) < order)
> >+			goto kswapd_try_sleep;
> 
> AFAICS now kswapd_try_to_sleep() will use the "requested" order. That's
> needed for proper wakeup_kcompactd(), but won't it prevent kswapd from
> actually going to sleep, because zone_balanced() in prepare-sleep will be
> false? So I think you need to give it both orders to do the right thing?
> 

You're right. There is a risk that kswapd stays awake longer in high
fragmentation scenarios.

Should be fixed now by passing in both orders.

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2016-06-16  8:30 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
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 01/27] mm, vmstat: Add infrastructure for per-node vmstats Mel Gorman
2016-06-10 13:31   ` Vlastimil Babka
2016-06-10 13:47     ` Mel Gorman
2016-06-13 17:26   ` Christoph Lameter
2016-06-14 14:25     ` Mel Gorman
2016-06-09 18:04 ` [PATCH 02/27] mm, vmscan: Move lru_lock to the node Mel Gorman
2016-06-10 16:39   ` Vlastimil Babka
2016-06-10 17:48     ` Peter Zijlstra
2016-06-14 14:41     ` Mel Gorman
2016-06-09 18:04 ` [PATCH 03/27] mm, vmscan: Move LRU lists to node Mel Gorman
2016-06-10 18:00   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 04/27] mm, vmscan: Begin reclaiming pages on a per-node basis Mel Gorman
2016-06-15 12:52   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 05/27] mm, vmscan: Have kswapd only scan based on the highest requested zone Mel Gorman
2016-06-15 13:13   ` Vlastimil Babka
2016-06-16  7:44     ` 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
2016-06-09 18:04 ` [PATCH 07/27] mm, vmscan: Remove balance gap Mel Gorman
2016-06-15 14:28   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 08/27] mm, vmscan: Simplify the logic deciding whether kswapd sleeps Mel Gorman
2016-06-15 15:18   ` Vlastimil Babka
2016-06-16  8:30     ` Mel Gorman [this message]
2016-06-16  9:16       ` Mel Gorman
2016-06-09 18:04 ` [PATCH 09/27] mm, vmscan: By default have direct reclaim only shrink once per node Mel Gorman
2016-06-16  8:59   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 10/27] mm, vmscan: Clear congestion, dirty and need for compaction on a per-node basis Mel Gorman
2016-06-16  9:29   ` Vlastimil Babka
2016-06-16 10:29     ` Mel Gorman
2016-06-09 18:04 ` [PATCH 11/27] mm: vmscan: Do not reclaim from kswapd if there is any eligible zone Mel Gorman
2016-06-16 10:08   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 12/27] mm, vmscan: Make shrink_node decisions more node-centric Mel Gorman
2016-06-16 13:35   ` Vlastimil Babka
2016-06-16 14:47     ` Mel Gorman
2016-06-09 18:04 ` [PATCH 13/27] mm, memcg: Move memcg limit enforcement from zones to nodes Mel Gorman
2016-06-16 15:06   ` Vlastimil Babka
2016-06-16 15:53     ` Mel Gorman
2016-06-09 18:04 ` [PATCH 14/27] mm, workingset: Make working set detection node-aware Mel Gorman
2016-06-16 15:13   ` Vlastimil Babka
2016-06-16 15:56     ` Mel Gorman
2016-06-09 18:04 ` [PATCH 15/27] mm, page_alloc: Consider dirtyable memory in terms of nodes Mel Gorman
2016-06-16 15:45   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 16/27] mm: Move page mapped accounting to the node Mel Gorman
2016-06-16 15:52   ` Vlastimil Babka
2016-06-16 16:04     ` Mel Gorman
2016-06-09 18:04 ` [PATCH 17/27] mm: Rename NR_ANON_PAGES to NR_ANON_MAPPED Mel Gorman
2016-06-17  8:28   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 18/27] mm: Move most file-based accounting to the node Mel Gorman
2016-06-17  8:35   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 19/27] mm: Move vmscan writes and file write " Mel Gorman
2016-06-17  8:51   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 20/27] mm, vmscan: Update classzone_idx if buffer_heads_over_limit Mel Gorman
2016-06-17  8:53   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 21/27] mm, vmscan: Only wakeup kswapd once per node for the requested classzone Mel Gorman
2016-06-17 10:46   ` Vlastimil Babka
2016-06-17 12:03     ` Mel Gorman
2016-06-09 18:04 ` [PATCH 22/27] mm: Convert zone_reclaim to node_reclaim Mel Gorman
2016-06-17 10:55   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 23/27] mm, vmscan: Add classzone information to tracepoints Mel Gorman
2016-06-17 10:57   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 24/27] mm, page_alloc: Remove fair zone allocation policy Mel Gorman
2016-06-17 11:27   ` Vlastimil Babka
2016-06-17 12:07     ` Mel Gorman
2016-06-09 18:04 ` [PATCH 25/27] mm: page_alloc: Cache the last node whose dirty limit is reached Mel Gorman
2016-06-17 11:31   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 26/27] mm: vmstat: Replace __count_zone_vm_events with a zone id equivalent Mel Gorman
2016-06-17 11:36   ` Vlastimil Babka
2016-06-09 18:04 ` [PATCH 27/27] mm: vmstat: Account per-zone stalls and pages skipped during reclaim Mel Gorman
2016-06-17 12:39   ` Vlastimil Babka
  -- strict thread matches above, loose matches on Subject: below --
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 08/27] mm, vmscan: Simplify the logic deciding whether kswapd sleeps Mel Gorman
2016-06-22 15:30   ` Vlastimil Babka
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 08/27] mm, vmscan: Simplify the logic deciding whether kswapd sleeps Mel Gorman
2016-04-06 11:19 [RFC PATCH 00/27] Move LRU page reclaim from zones to nodes v3 Mel Gorman
2016-04-06 11:20 ` [PATCH 08/27] mm, vmscan: Simplify the logic deciding whether kswapd sleeps Mel Gorman

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