Re: Hugepages - benefits / drawbacks

David,

In my mind ISM is related to shared memory, could it be used for private memory allocation ?

thanks
--romas

On Tue, Oct 7, 2008 at 6:38 PM, David Miller <David.J.Miller_at_sun.com> wrote:

> Hi Roman,
>
> I believe this was obsoleted in Oracle 10.2, which is why you don't see it
> do
> anything.
>
> The idea behind the parameter (_use_ism_for_pga) was that Solaris only
> allowed large pages for ISM segments prior to Solaris 9 and in Solaris 9,
> using large pages for non-ISM segments required manual intervention.
>
> In Solaris 10, large pages became usable for many different kinds of memory
> depending on the allocations for each. Thus it became possible to use
> large pages for the PGA without having to put it in ISM.
>
> But it still will depend on how the PGA is allocated. With 10.2.0.3, you
> can specify the "_realfree_heap_pagesize_hint = 4194304" and it will
> use 4 MB pages for the heap. These won't be ISM, but using "pmap -xs"
> will show the segments with a pagesize of 4M (assuming you're on SPARC).
>
> The benefits of this will depend entirely on how your application uses
> the PGA. With large hash or sort areas needed, large pages can help
> performance significantly. For other applications, the benefit may
> be minimal.
>
> Regards,
>
> Dave Miller
>

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