Hi Minchan,
> Nick's original goal is to prevent OOM killing until all zone we're
> interested in are unreclaimable and whether zone is reclaimable or not
> depends on kswapd. And Nick's original solution is just peeking
> zone->all_unreclaimable but I made it dirty when we are considering
> kswapd freeze in hibernation. So I think we still need it to handle
> kswapd freeze problem and we should add original behavior we missed at
> that time like below.
>
> static bool zone_reclaimable(struct zone *zone)
> {
> if (zone->all_unreclaimable)
> return false;
>
> return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
> }
>
> If you remove the logic, the problem Nick addressed would be showed
> up, again. How about addressing the problem in your patch? If you
> remove the logic, __alloc_pages_direct_reclaim lose the chance calling
> dran_all_pages. Of course, it was a side effect but we should handle
> it.
Ok, you are successfull to persuade me. lost drain_all_pages() chance has
a risk.
> And my last concern is we are going on right way?
> I think fundamental cause of this problem is page_scanned and
> all_unreclaimable is race so isn't the approach fixing the race right
> way?
Hmm..
If we can avoid lock, we should. I think. that's performance reason.
therefore I'd like to cap the issue in do_try_to_free_pages(). it's
slow path.
Is the following patch acceptable to you? it is
o rewrote the description
o avoid mix to use zone->all_unreclaimable and zone->pages_scanned
o avoid to reintroduce hibernation issue
o don't touch fast path
> If it is hard or very costly, your and my approach will be fallback.
-----------------------------------------------------------------
>From f3d277057ad3a092aa1c94244f0ed0d3ebe5411c Mon Sep 17 00:00:00 2001
From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Date: Sat, 14 May 2011 05:07:48 +0900
Subject: [PATCH] vmscan: all_unreclaimable() use zone->all_unreclaimable as the name
all_unreclaimable check in direct reclaim has been introduced at 2.6.19
by following commit.
2006 Sep 25; commit 408d8544; oom: use unreclaimable info
And it went through strange history. firstly, following commit broke
the logic unintentionally.
2008 Apr 29; commit a41f24ea; page allocator: smarter retry of
costly-order allocations
Two years later, I've found obvious meaningless code fragment and
restored original intention by following commit.
2010 Jun 04; commit bb21c7ce; vmscan: fix do_try_to_free_pages()
return value when priority==0
But, the logic didn't works when 32bit highmem system goes hibernation
and Minchan slightly changed the algorithm and fixed it .
2010 Sep 22: commit d1908362: vmscan: check all_unreclaimable
in direct reclaim path
But, recently, Andrey Vagin found the new corner case. Look,
struct zone {
..
int all_unreclaimable;
..
unsigned long pages_scanned;
..
}
zone->all_unreclaimable and zone->pages_scanned are neigher atomic
variables nor protected by lock. Therefore zones can become a state
of zone->page_scanned=0 and zone->all_unreclaimable=1. In this case,
current all_unreclaimable() return false even though
zone->all_unreclaimabe=1.
Is this ignorable minor issue? No. Unfortunatelly, x86 has very
small dma zone and it become zone->all_unreclamble=1 easily. and
if it become all_unreclaimable=1, it never restore all_unreclaimable=0.
Why? if all_unreclaimable=1, vmscan only try DEF_PRIORITY reclaim and
a-few-lru-pages>>DEF_PRIORITY always makes 0. that mean no page scan
at all!
Eventually, oom-killer never works on such systems. That said, we
can't use zone->pages_scanned for this purpose. This patch restore
all_unreclaimable() use zone->all_unreclaimable as old. and in addition,
to add oom_killer_disabled check to avoid reintroduce the issue of
commit d1908362.
Reported-by: Andrey Vagin <avagin@xxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxxxx>
Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
---
mm/vmscan.c | 24 +++++++++++++-----------
1 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 060e4c1..54ac548 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -41,6 +41,7 @@
#include <linux/memcontrol.h>
#include <linux/delayacct.h>
#include <linux/sysctl.h>
+#include <linux/oom.h>
#include <asm/tlbflush.h>
#include <asm/div64.h>
@@ -1988,17 +1989,12 @@ static bool zone_reclaimable(struct zone *zone)
return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
}
-/*
- * As hibernation is going on, kswapd is freezed so that it can't mark
- * the zone into all_unreclaimable. It can't handle OOM during hibernation.
- * So let's check zone's unreclaimable in direct reclaim as well as kswapd.
- */
+/* All zones in zonelist are unreclaimable? */
static bool all_unreclaimable(struct zonelist *zonelist,
struct scan_control *sc)
{
struct zoneref *z;
struct zone *zone;
- bool all_unreclaimable = true;
for_each_zone_zonelist_nodemask(zone, z, zonelist,
gfp_zone(sc->gfp_mask), sc->nodemask) {
@@ -2006,13 +2002,11 @@ static bool all_unreclaimable(struct zonelist *zonelist,
continue;
if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
continue;
- if (zone_reclaimable(zone)) {
- all_unreclaimable = false;
- break;
- }
+ if (!zone->all_unreclaimable)
+ return false;
}
- return all_unreclaimable;
+ return true;
}
/*
@@ -2108,6 +2102,14 @@ out:
if (sc->nr_reclaimed)
return sc->nr_reclaimed;
+ /*
+ * As hibernation is going on, kswapd is freezed so that it can't mark
+ * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
+ * check.
+ */
+ if (oom_killer_disabled)
+ return 0;
+
/* top priority shrink_zones still had more to do? don't OOM, then */
if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
return 1;
--
1.6.5.2
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