/proc/slabinfo gives information about memory usage on the slab level. Linux kernels uses slab pools to manage memory above the page level. Commonly used objects have their own slab pools. Instead of parsing the highly verbose /proc/slabinfo file manually, the /usr/bin/slabtop program displays kernel slab cache information in real time. This program allows for custom configurations, including column sorting and screen refreshing.

Sample slabtop :

# /usr/bin/slaptop

 Active / Total Objects (% used)    : 286703 / 730599 (39.2%)
 Active / Total Slabs (% used)      : 46347 / 46357 (100.0%)
 Active / Total Caches (% used)     : 95 / 142 (66.9%)
 Active / Total Size (% used)       : 89858.38K / 179248.09K (50.1%)
 Minimum / Average / Maximum Object : 0.01K / 0.25K / 128.00K

  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
279330  86167  30%    0.25K  18622       15     74488K size-256
 88046  44665  50%    0.27K   6289       14     25156K radix_tree_node
 79350   3621   4%    0.05K   1058       75      4232K buffer_head
 71266  32169  45%    0.15K   2741       26     10964K dentry_cache

Important parameters in /proc/slabinfo & slaptop are as below :

  • OBJS — The total number of objects (memory blocks), including those in use (allocated), and some spares not in use.
  • ACTIVE — The number of objects (memory blocks) that are in use (allocated).
  • USE — Percentage of total objects that are active. ((ACTIVE/OBJS)(100))
  • OBJ SIZE — The size of the objects.
  • SLABS — The total number of slabs.
  • OBJ/SLAB — The number of objects that fit into a slab.
  • CACHE SIZE — The cache size of the slab.
  • NAME — The name of the slab.

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