[Crash-utility] How to parse out kmem output?

[Dave Anderson]

----- Original Message -----
> Hi list,
> 
> I am current tracking one issue related with memory.
> What I want to know if a kernel address which is alloced by kmalloc,
> 1. whether that address is already freed or not
> 2. if not freed, could I know which task or struct is owning that
> range?
> 
> I am also try to use the kmem command to get more info,
> but I don't know the meaning for its output...
> Like "CACHE"/"ALLOCATED"/"TOTAL"/"SLABS" member,

The CACHE is the kmem_cache structure address.
The ALLOCATED total is the number of objects that have been
allocated from the CACHE.
The TOTAL is the maximum number of objects in the CACHE.
The SLABS is the number of of SSIZE-sized slabs that are
current being used to create the TOTAL number of objects.

> what are they referring to?
> And according to "FREE / [ALLOCATED]" as below, does it
> mean that 0xe1416acc already be freed?
> 
> crash> kmem -S 0xe1416acc
> CACHE    NAME                 OBJSIZE  ALLOCATED     TOTAL  SLABS
>  SSIZE
> e0002400 kmalloc-2048            2048        156       160     10
>    32k
>   SLAB      MEMORY    NODE  TOTAL  ALLOCATED  FREE
>   c1628200  e1410000     0     12         12     0
>   FREE / [ALLOCATED]
>   [e1410000]
>   [e1410800]
>   [e1411000]
>   [e1411800]
>    e1412000  (cpu 0 cache)
>    e1412800  (cpu 0 cache)
>    e1413000  (cpu 0 cache)
>    e1413800  (cpu 0 cache)
>    e1414000  (cpu 0 cache)
>    e1414800  (cpu 0 cache)
>    e1415000  (cpu 0 cache)
>   [e1415800]
> crash>

The SLUB display indicates that there are 12 objects allocated
from the "kmalloc-2048" cache, and either they are currently
in use, or they are sitting on the cpu 0 per-cpu cache.  The 
address that you entered would "fit" into the 32k slab page, 
but it doesn't seem to be allocated or sitting in the cpu 0 cache.

I believe that means that the object is currently free.

> Also seems current kmem only support SLAB, right?

Wait, isn't your kernel CONFIG_SLUB?  Enter "help -v" and look
at the flags field.  It will show either KMALLOC_SLUB or KMALLOC_SLAB.
CONFIG_SLOB is not supported.

Dave


> If memory is allocated with like SLUB or SLOB, could the kmem
> still handle it?
> 
> Thanks,
> Lei
> 
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