understanding linux cache and free command

understanding linux cache and free command

[Prashant Batra]

Hi All,

I have created few memory cache areas using "kmem_cache_create" and 
using it to allocate some memory.

What I observe after some cache_alloc's and cache_free's is that 
/proc/slabinfo entries for my objects are good, meaning the number of 
objects go back to 0 after they are freed.

But linux "free" command shows that some of the objects are cached and 
that keeps on increasing. I am not able to understand this behavior. Is 
it that kernel keeps the cache objects even after they are freed?

#cat /proc/slabinfo
my_cache         200    200   4096    1    1 : tunables   24   12    8 : 
slabdata    200    200      0

It shows 200 allocated objects from "my_cache"

and

#free -lm

             total       used       free     shared    buffers     cached
Mem:         48340        610      47730          0         96       130

the cached objects keep on growing.

After 5 mins in which I am doing some alloc and free-
             total       used       free     shared    buffers     cached
Mem:        48340        616      47723          0         96        137

/proc/slabinfo remains the same.

Any help is appreciated.

Thanks,
Prashant
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Re: understanding linux cache and free command

[Prashant Batra]

Adding netdev for a bigger audience.

On Tuesday, February 26, 2013 6:18:48 PM, Prashant Batra wrote:
> Hi All,
>
> I have created few memory cache areas using "kmem_cache_create" and
> using it to allocate some memory.
>
> What I observe after some cache_alloc's and cache_free's is that
> /proc/slabinfo entries for my objects are good, meaning the number of
> objects go back to 0 after they are freed.
>
> But linux "free" command shows that some of the objects are cached and
> that keeps on increasing. I am not able to understand this behavior.
> Is it that kernel keeps the cache objects even after they are freed?
>
> #cat /proc/slabinfo
> my_cache         200    200   4096    1    1 : tunables   24   12    8
> : slabdata    200    200      0
>
> It shows 200 allocated objects from "my_cache"
>
> and
>
> #free -lm
>
>             total       used       free     shared    buffers     cached
> Mem:         48340        610      47730          0         96       130
>
> the cached objects keep on growing.
>
> After 5 mins in which I am doing some alloc and free-
>             total       used       free     shared    buffers     cached
> Mem:        48340        616      47723          0         96        137
>
> /proc/slabinfo remains the same.
>
> Any help is appreciated.
>
> Thanks,
> Prashant