Re: [PATCH] mm: check zone->all_unreclaimable in all_unreclaimable()
From: Andrew Vagin
Date: Sat Mar 05 2011 - 11:42:21 EST
On 03/05/2011 06:53 PM, Minchan Kim wrote:
On Sat, Mar 05, 2011 at 06:34:37PM +0300, Andrew Vagin wrote:
On 03/05/2011 06:20 PM, Minchan Kim wrote:
On Sat, Mar 05, 2011 at 02:44:16PM +0300, Andrey Vagin wrote:
Check zone->all_unreclaimable in all_unreclaimable(), otherwise the
kernel may hang up, because shrink_zones() will do nothing, but
all_unreclaimable() will say, that zone has reclaimable pages.
do_try_to_free_pages()
shrink_zones()
for_each_zone
if (zone->all_unreclaimable)
continue
if !all_unreclaimable(zonelist, sc)
return 1
__alloc_pages_slowpath()
retry:
did_some_progress = do_try_to_free_pages(page)
...
if (!page&& did_some_progress)
retry;
Signed-off-by: Andrey Vagin<avagin@xxxxxxxxxx>
---
mm/vmscan.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6771ea7..1c056f7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2002,6 +2002,8 @@ static bool all_unreclaimable(struct zonelist *zonelist,
for_each_zone_zonelist_nodemask(zone, z, zonelist,
gfp_zone(sc->gfp_mask), sc->nodemask) {
+ if (zone->all_unreclaimable)
+ continue;
if (!populated_zone(zone))
continue;
if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
zone_reclaimable checks it. Isn't it enough?
I sent one more patch [PATCH] mm: skip zombie in OOM-killer.
This two patches are enough.
Sorry if I confused you.
I mean zone->all_unreclaimable become true if !zone_reclaimable in balance_pgdat.
zone_reclaimable compares recent pages_scanned with the number of zone lru pages.
So too many page scanning in small lru pages makes the zone to unreclaimable zone.
In all_unreclaimable, we calls zone_reclaimable to detect it.
It's the same thing with your patch.
balance_pgdat set zone->all_unreclaimable, but the problem is that it is
cleaned late.
The problem is that zone->all_unreclaimable = True, but
zone_reclaimable() returns True too.
zone->all_unreclaimable will be cleaned in free_*_pages, but this may be
late. It is enough allocate one page from page cache, that
zone_reclaimable() returns True and zone->all_unreclaimable becomes True.
Does the hang up really happen or see it by code review?
Yes. You can reproduce it for help the attached python program. It's
not very clever:)
It make the following actions in loop:
1. fork
2. mmap
3. touch memory
4. read memory
5. munmmap
It seems the test program makes fork bombs and memory hogging.
If you applied this patch, the problem is gone?
Yes.
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import sys, time, mmap, os
from subprocess import Popen, PIPE
import random
global mem_size
def info(msg):
pid = os.getpid()
print>> sys.stderr, "%s: %s" % (pid, msg)
sys.stderr.flush()
def memory_loop(cmd = "a"):
"""
cmd may be:
c: check memory
else: touch memory
"""
c = 0
for j in xrange(0, mem_size):
if cmd == "c":
if f[j<<12] != chr(j % 255):
info("Data corruption")
sys.exit(1)
else:
f[j<<12] = chr(j % 255)
while True:
pid = os.fork()
if (pid != 0):
mem_size = random.randint(0, 56 * 4096)
f = mmap.mmap(-1, mem_size<< 12, mmap.MAP_ANONYMOUS|mmap.MAP_PRIVATE)
memory_loop()
memory_loop("c")
f.close()
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