Re: SLUB

[Mark Seger <Mark.Seger@hp.com>]

> I think we better keep it public (so that it goes into the archive). Here 
> a short description of the field in /sys/kernel/slab/<slabcache> that you 
> would need
>
> -r--r--r-- 1 root root 4096 Dec 20 11:41 object_size
>
> The size of an object. Subtract slab_size - object_size and you have the 
> per object overhead generated by alignements and slab metadata. Does not 
> change you only need to read this once.
>
> -r--r--r-- 1 root root 4096 Dec 20 11:41 objects
>
> Number of objects in use. This changes and you may want to monitor it.
>
> -r--r--r-- 1 root root 4096 Dec 20 11:41 slab_size
>
> Total memory used for a single object. Read this only once.
>
> -r--r--r-- 1 root root 4096 Dec 20 11:41 slabs
>
> Number of slab pages in use for this slab cache. May change if slab is 
> extended.
>   
Sorry for being confused, but I thought that a slab was made up of a 
number of objects and above you're saying slab_size is the size of 
single object.  Furthermore, looking at /sys/slab/shmem_inode_cache I see:

object_size = 960
objs_per_slab = 4

which implies a slab is made up more than one object, so which is it?  
could it be a simple matter of clearer names?  I also see

slab_size = 968

which certainly supports your statement about this being the size of an 
object and it looks like there is 8 bytes of overhead.  finally, I also see

objects = 242

and objects * obj_per_slab = slabsize.  is that a coincidence?

-mark


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