Red Hat ENTERPRISE LINUX AS 2.1 - Installationsanleitung PDF herunterladen (Seite 41)

Verifying Asynchronous I/O Usage

The numbers in red (number of active objects) show whether Oracle makes asynchronous I/O calls.

The output will look a little bit different in Red Hat Enterprise Linux 4 and 5. However, the numbers

in red will show same behavior in Red Hat Enterprise Linux 3 and Red Hat Enterprise Linux 4 and 5.

The first column displays the cache names kioctx and kiocb. The second column shows the number

of active objects currently in use. And the third column shows how many objects are available in total,

used and unused.

To see kernel slab cache information in real time, you can also use the slabtop command:

$ slabtop

Active / Total Objects (% used) : 293568 / 567030 (51.8%)

Active / Total Slabs (% used) : 36283 / 36283 (100.0%)

Active / Total Caches (% used) : 88 / 125 (70.4%)

Active / Total Size (% used) : 81285.56K / 132176.36K (61.5%)

Minimum / Average / Maximum Object : 0.01K / 0.23K / 128.00K

OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME

178684 78396 43% 0.12K 5764 31 23056K size-128

127632 36292 28% 0.16K 5318 24 21272K dentry_cache

102815 74009 71% 0.69K 20563 5 82252K ext3_inode_cache

71775 32434 45% 0.05K 957 75 3828K buffer_head

19460 15050 77% 0.27K 1390 14 5560K radix_tree_node

13090 13015 99% 0.03K 110 119 440K avtab_node

12495 11956 95% 0.03K 105 119 420K size-32

...

Slab caches are a special memory pool in the kernel for adding and removing objects, such as data

structures or data buffers, of the same size. Its a cache for commonly used objects where the kernel

does not have to re-allocate and initialize the object each time it is being reused, and free the object

each time it is being destroyed. The slab allocator scheme basically prevents memory fragmentation

and it prevents the kernel from spending too much time allocating, initializing, and freeing the same

objects.

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Red Hat ENTERPRISE LINUX AS 2.1 - Installationsanleitung Seite 41