linux-kernel - Re: kswapd craziness in 3.7

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Date:	Sat, 08 Dec 2012 11:35:46 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Zdenek Kabelac <zkabelac@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	George Spelvin <linux@...izon.com>,
	Johannes Hirte <johannes.hirte@....tu-ilmenau.de>,
	Thorsten Leemhuis <fedora@...mhuis.info>,
	Tomas Racek <tracek@...hat.com>, Jan Kara <jack@...e.cz>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Josh Boyer <jwboyer@...il.com>, Valdis.Kletnieks@...edu,
	Bruno Wolff III <bruno@...ff.to>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: kswapd craziness in 3.7

On 12/04/2012 05:11 PM, Johannes Weiner wrote:
> On Tue, Dec 04, 2012 at 10:15:09AM +0100, Jiri Slaby wrote:
>> It does not apply to -next :/. Should I try anything else?
> 
> The COMPACTION_BUILD changed to IS_ENABLED(CONFIG_COMPACTION), below
> is a -next patch.  I hope you don't run into other problems that come
> out of -next craziness, because Linus is kinda waiting for this to be
> resolved to release 3.8.  If you've always tested against -next so far
> and it worked otherwise, don't change the environment now, please.  If
> you just started, it would make more sense to test based on 3.7-rc8.
> 
> Thanks!
> 
> ---
> From: Johannes Weiner <hannes@...xchg.org>
> Subject: [patch] mm: vmscan: do not keep kswapd looping forever due
>  to individual uncompactable zones
> 
> When a zone meets its high watermark and is compactable in case of
> higher order allocations, it contributes to the percentage of the
> node's memory that is considered balanced.
> 
> This requirement, that a node be only partially balanced, came about
> when kswapd was desparately trying to balance tiny zones when all
> bigger zones in the node had plenty of free memory.  Arguably, the
> same should apply to compaction: if a significant part of the node is
> balanced enough to run compaction, do not get hung up on that tiny
> zone that might never get in shape.
> 
> When the compaction logic in kswapd is reached, we know that at least
> 25% of the node's memory is balanced properly for compaction (see
> zone_balanced and pgdat_balanced).  Remove the individual zone checks
> that restart the kswapd cycle.
> 
> Otherwise, we may observe more endless looping in kswapd where the
> compaction code loops back to reclaim because of a single zone and
> reclaim does nothing because the node is considered balanced overall.
> 
> Reported-by: Thorsten Leemhuis <fedora@...mhuis.info>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Looks like it's gone with this patch now. Hopefully the send button
won't trigger the issue the same as the last time :).

> ---
>  mm/vmscan.c | 16 ----------------
>  1 file changed, 16 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 3b0aef4..486100f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2806,22 +2806,6 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>  			if (!populated_zone(zone))
>  				continue;
>  
> -			if (zone->all_unreclaimable &&
> -			    sc.priority != DEF_PRIORITY)
> -				continue;
> -
> -			/* Would compaction fail due to lack of free memory? */
> -			if (IS_ENABLED(CONFIG_COMPACTION) &&
> -			    compaction_suitable(zone, order) == COMPACT_SKIPPED)
> -				goto loop_again;
> -
> -			/* Confirm the zone is balanced for order-0 */
> -			if (!zone_watermark_ok(zone, 0,
> -					high_wmark_pages(zone), 0, 0)) {
> -				order = sc.order = 0;
> -				goto loop_again;
> -			}
> -
>  			/* Check if the memory needs to be defragmented. */
>  			if (zone_watermark_ok(zone, order,
>  				    low_wmark_pages(zone), *classzone_idx, 0))
> 


-- 
js
suse labs
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