linux-kernel - [PATCH] Revert "mm: vmscan: scale number of pages reclaimed by reclaim/compaction based on failures"

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 5 Nov 2012 14:24:49 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Zdenek Kabelac <zkabelac@...hat.com>, Valdis.Kletnieks@...edu,
	Jiri Slaby <jirislaby@...il.com>, linux-mm@...ck.org,
	Rik van Riel <riel@...hat.com>, Jiri Slaby <jslaby@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] Revert "mm: vmscan: scale number of pages reclaimed by
 reclaim/compaction based on failures"

Jiri Slaby reported the following:

	(It's an effective revert of "mm: vmscan: scale number of pages
	reclaimed by reclaim/compaction based on failures".) Given kswapd
	had hours of runtime in ps/top output yesterday in the morning
	and after the revert it's now 2 minutes in sum for the last 24h,
	I would say, it's gone.

The intention of the patch in question was to compensate for the loss
of lumpy reclaim. Part of the reason lumpy reclaim worked is because
it aggressively reclaimed pages and this patch was meant to be a sane
compromise.

When compaction fails, it gets deferred and both compaction and
reclaim/compaction is deferred avoid excessive reclaim. However, since
commit c6543459 (mm: remove __GFP_NO_KSWAPD), kswapd is woken up each time
and continues reclaiming which was not taken into account when the patch
was developed.

Attempts to address the problem ended up just changing the shape of the
problem instead of fixing it. The release window gets closer and while a
THP allocation failing is not a major problem, kswapd chewing up a lot of
CPU is. This patch reverts "mm: vmscan: scale number of pages reclaimed
by reclaim/compaction based on failures" and will be revisited in the future.

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 mm/vmscan.c |   25 -------------------------
 1 file changed, 25 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2624edc..e081ee8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1760,28 +1760,6 @@ static bool in_reclaim_compaction(struct scan_control *sc)
 	return false;
 }
 
-#ifdef CONFIG_COMPACTION
-/*
- * If compaction is deferred for sc->order then scale the number of pages
- * reclaimed based on the number of consecutive allocation failures
- */
-static unsigned long scale_for_compaction(unsigned long pages_for_compaction,
-			struct lruvec *lruvec, struct scan_control *sc)
-{
-	struct zone *zone = lruvec_zone(lruvec);
-
-	if (zone->compact_order_failed <= sc->order)
-		pages_for_compaction <<= zone->compact_defer_shift;
-	return pages_for_compaction;
-}
-#else
-static unsigned long scale_for_compaction(unsigned long pages_for_compaction,
-			struct lruvec *lruvec, struct scan_control *sc)
-{
-	return pages_for_compaction;
-}
-#endif
-
 /*
  * Reclaim/compaction is used for high-order allocation requests. It reclaims
  * order-0 pages before compacting the zone. should_continue_reclaim() returns
@@ -1829,9 +1807,6 @@ static inline bool should_continue_reclaim(struct lruvec *lruvec,
 	 * inactive lists are large enough, continue reclaiming
 	 */
 	pages_for_compaction = (2UL << sc->order);
-
-	pages_for_compaction = scale_for_compaction(pages_for_compaction,
-						    lruvec, sc);
 	inactive_lru_pages = get_lru_size(lruvec, LRU_INACTIVE_FILE);
 	if (nr_swap_pages > 0)
 		inactive_lru_pages += get_lru_size(lruvec, LRU_INACTIVE_ANON);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/