linux-kernel - Re: [PATCH 1/5] vmscan: remove all_unreclaimable check from direct reclaim path completely

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Date:	Wed, 23 Mar 2011 16:13:21 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-mm <linux-mm@...ck.org>,
	Andrey Vagin <avagin@...nvz.org>,
	Hugh Dickins <hughd@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...nel.dk>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 1/5] vmscan: remove all_unreclaimable check from direct reclaim path completely

> Okay. I got it.
> 
> The problem is following as.
> By the race the free_pcppages_bulk and balance_pgdat, it is possible
> zone->all_unreclaimable = 1 and zone->pages_scanned = 0.
> DMA zone have few LRU pages and in case of no-swap and big memory
> pressure, there could be a just a page in inactive file list like your
> example. (anon lru pages isn't important in case of non-swap system)
> In such case, shrink_zones doesn't scan the page at all until priority
> become 0 as get_scan_count does scan >>= priority(it's mostly zero).

Nope.

                        if (zone->all_unreclaimable && priority != DEF_PRIORITY)
                                continue;

This tow lines mean, all_unreclaimable prevent priority 0 reclaim.


> And although priority become 0, nr_scan_try_batch returns zero until
> saved pages become 32. So for scanning the page, at least, we need 32
> times iteration of priority 12..0.  If system has fork-bomb, it is
> almost livelock.

Therefore, 1000 times get_scan_count(DEF_PRIORITY) takes 1000 times no-op.

> 
> If is is right, how about this?

Boo.
You seems forgot why you introduced current all_unreclaimable() function.
While hibernation, we can't trust all_unreclaimable.

That's the reason why I proposed following patch when you introduced
all_unreclaimable().


---
 mm/vmscan.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c391c32..1919d8a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -40,6 +40,7 @@
 #include <linux/memcontrol.h>
 #include <linux/delayacct.h>
 #include <linux/sysctl.h>
+#include <linux/oom.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -1931,7 +1932,7 @@ out:
 		return sc->nr_reclaimed;
 
 	/* top priority shrink_zones still had more to do? don't OOM, then */
-	if (scanning_global_lru(sc) && !all_unreclaimable)
+	if (scanning_global_lru(sc) && !all_unreclaimable && !oom_killer_disabled)
 		return 1;
 
 	return 0;
-- 
1.6.5.2





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