linux-kernel - huge debug_objects_cache. swapping but 25% mem free

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Date:	Mon, 30 Jan 2012 16:40:48 +0100
From:	Johannes Stezenbach <js@...21.net>
To:	linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: huge debug_objects_cache. swapping but 25% mem free

Hi,

linux-3.2.2, Asus P8H67-V board with 4G RAM and Core i5-2400S.
I enabled CONFIG_DEBUG_OBJECTS since I had a random BUG
after resume and wanted to see if it turns something up.
http://lkml.org/lkml/2012/1/26/63

After letting the machine run over the weekend and doing
a cross toolchain build from remote, today I find the
machine working very sluggish, hitting the disk all the time.
(single SATA, no SSD, 4G swap partition)

According to slabtop debug_objects_cache eats half the
memory, is this expected?  The Kconfig help text does not
suggest it.

I also wonder why it starts swapping with MemFree > 1G.

slabtop:

  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
  5085938 5085926  99%    0.36K 231445       22   1851560K debug_objects_cache
   19224  15423  80%    0.58K    712       27     11392K dentry

/sys/kernel/debug/debug_objects/stats:
max_chain     :927
warnings      :0
fixups        :0
pool_free     :259
pool_min_free :252
pool_used     :5085667
pool_max_used :5085670

/proc/meminfo
MemTotal:        3938800 kB
MemFree:         1146876 kB
Buffers:           16788 kB
Cached:           143692 kB
SwapCached:        68244 kB
Active:           382824 kB
Inactive:         389504 kB
Active(anon):     328808 kB
Inactive(anon):   326812 kB
Active(file):      54016 kB
Inactive(file):    62692 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:       3903484 kB
SwapFree:        3382456 kB
Dirty:                 4 kB
Writeback:             0 kB
AnonPages:        552520 kB
Mapped:            31600 kB
Shmem:             43772 kB
Slab:            1950624 kB
SReclaimable:      43304 kB
SUnreclaim:      1907320 kB
KernelStack:        1720 kB
PageTables:         6124 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     5872884 kB
Committed_AS:    1769420 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      356308 kB
VmallocChunk:   34359348840 kB
DirectMap4k:       12288 kB

config attached

Thanks
Johannes

View attachment "config-3.2.2" of type "text/plain" (73992 bytes)