Watching slab usage with slabtop

The Linux kernel uses a slab based allocator to allocate kernel memory. Inside each slab is a collection of objects that have been allocated by one or more kernel subsystems. To monitor slab utilization in realtime, most modern day Linux distributions ship with the slaptop utility. When slabtop is run without any arguments, it displays a nice slab usage summary, and provides details of how various slabs are being used:

$ slabtop

 Active / Total Objects (% used)    : 220410 / 234629 (93.9%)
 Active / Total Slabs (% used)      : 4728 / 4728 (100.0%)
 Active / Total Caches (% used)     : 91 / 139 (65.5%)
 Active / Total Size (% used)       : 16609.59K / 18017.14K (92.2%)
 Minimum / Average / Maximum Object : 0.01K / 0.08K / 128.00K

  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME                   
 80591  80494  99%    0.02K    397      203      1588K avtab_node
 53562  53562 100%    0.03K    474      113      1896K size-32
 35108  35099  99%    0.05K    524       67      2096K buffer_head
  7378   7377  99%    0.27K    527       14      2108K radix_tree_node
  7182   7182 100%    0.14K    266       27      1064K dentry_cache
  6499   6497  99%    0.05K     97       67       388K selinux_inode_security
  5460   5398  98%    0.04K     65       84       260K sysfs_dir_cache
  3953   3425  86%    0.06K     67       59       268K size-64
  3663   3644  99%    0.41K    407        9      1628K inode_cache
  3654    479  13%    0.02K     18      203        72K biovec-1   
  2904   1882  64%    0.09K     66       44       264K vm_area_struct
  2580   2442  94%    0.12K     86       30       344K size-128
  2080    924  44%    0.19K    104       20       416K filp
  2070    744  35%    0.12K     69       30       276K bio 
  1944    660  33%    0.05K     27       72       108K journal_head
  1896   1892  99%    0.59K    316        6      1264K ext3_inode_cache
  1595    525  32%    0.02K     11      145        44K anon_vma
  1288   1209  93%    0.04K     14       92        56K Acpi-Operand
   845    730  86%    0.02K      5      169        20K Acpi-Namespace
   648    511  78%    0.05K      9       72        36K avc_node
   540    471  87%    0.43K     60        9       240K proc_inode_cache

These is a sweet utility, and is another one of those tools that should be in every Linux administrators tool belt.

1 thought on “Watching slab usage with slabtop”

  1. Hi.

    Do you know, how should be interpreted the information provided by slabtop?

    I mean, in “top” a superhigh _USE_ percent is bad, that would be procesor usage, but in slabtop almost every single cache is at 100%.
    Does this means that my system is highly broken? I guess not.

    Can we extrapolate some other information from it? Like what is the most active hardware taking my battery off ?

    Thanks

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