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

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Message-ID: <20120201182932.GA15518@sig21.net>
Date:	Wed, 1 Feb 2012 19:29:32 +0100
From:	Johannes Stezenbach <js@...21.net>
To:	linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: huge debug_objects_cache. swapping but 25% mem free

On Mon, Jan 30, 2012 at 04:40:48PM +0100, Johannes Stezenbach wrote:
> 
> According to slabtop debug_objects_cache eats half the
> memory, is this expected?  The Kconfig help text does not
> suggest it.

FWIW, today after running full backup using rsync:

  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
4025450 4025447  99%    0.36K 183977       22   1471816K debug_objects_cache
170266  87241  51%    1.74K   9645       18    308640K ext3_inode_cache
 54855  40215  73%    0.58K   2034       27     32544K dentry
 38124  12474  32%    0.42K   2119       18     16952K buffer_head
 17794  17464  98%    0.51K    574       31      9184K sysfs_dir_cache
 11434   8494  74%    0.87K    713       18     11408K radix_tree_node
 11400   5570  48%    0.38K    570       20      4560K kmalloc-64

/sys/kernel/debug/debug_objects/stats:
max_chain     :870
warnings      :0
fixups        :0
pool_free     :258
pool_min_free :252
pool_used     :4025193
pool_max_used :4025195


then after "echo 3 >/proc/sys/vm/drop_caches":

  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
4030488 4030485  99%    0.36K 184206       22   1473648K debug_objects_cache
 17955   9071  50%    0.58K    665       27     10640K dentry
 17763  17455  98%    0.51K    573       31      9168K sysfs_dir_cache
  9408   9156  97%    0.33K    392       24      3136K kmalloc-8


I'm still not sure if this is normal behaviour of DEBUG_OBJECTS or a bug?


Anyway, I'm going to turn it off now.


Johannes
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