VM question - accounting of SysV SHM

VM question - accounting of SysV SHM

[Lee Revell]

Sorry to ask this question on the list but I've Googled and found nothing.

Is system V shared memory accounted for as Cached, or as normal
application memory?

I have an application that uses SysV shared memory and O_DIRECT for
all IO, but when it starts up, the cached column in vmstat seems to go
up by the amount of shared memory allocated.

Lee

Re: VM question - accounting of SysV SHM

[Rik van Riel]

On Wed, 17 Oct 2007 16:49:07 -0400
"Lee Revell" <rlrevell@joe-job.com> wrote:

> Sorry to ask this question on the list but I've Googled and found
> nothing.
> 
> Is system V shared memory accounted for as Cached, or as normal
> application memory?

Cached.

Shared memory segments basically are tmpfs files.

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan

Re: VM question - accounting of SysV SHM

[Lee Revell]

On 10/17/07, Rik van Riel <riel@redhat.com> wrote:
> On Wed, 17 Oct 2007 16:49:07 -0400
> "Lee Revell" <rlrevell@joe-job.com> wrote:
>
> > Sorry to ask this question on the list but I've Googled and found
> > nothing.
> >
> > Is system V shared memory accounted for as Cached, or as normal
> > application memory?
>
> Cached.
>
> Shared memory segments basically are tmpfs files.

Thanks!

Are there any plans to track it separately in a future kernel release?

I've also noticed that if huge pages are used for the shared memory,
they are not accounted for as cached - I have a 56GB huge page pool
but cached is only 6GB.  Is this behavior specific to huge pages?

Finally, are these quirks documented anywhere?

Lee