Re: Hugepages - benefits / drawbacks

From: Yong Huang <>
Date: Thu, 9 Oct 2008 09:31:27 -0700 (PDT)
Message-ID: <>

Thanks, David. That finally anwers my (and maybe Roman's) question: How can ISM be used for PGA? Just because there's a shared (or rather, sharable) memory segment created doesn't mean it must be shared. Solaris ISM or Linux HugePages is just a name for this technology. It has all these features: (a) sharing page tables between processes, (b) large memory page size, (c) locking pages in memory (related to (a)). The name ISM emphasizes (a), while HugePages emphasizes (b). The Oracle parameter _use_ism_for_pga confused me simply because they used the term ism in it. If it was called _use_largepage_for_pga without any change in its implementation, I wouldn't ask the question.

Yong Huang

> From: David Miller <David.J.Miller_at_Sun.COM>
> Hi Roman,
> ISM is indeed shared memory, but it is possible to allocate it and only
> use it in one place, i.e. a single process's PGA. Once it's mapped into
> the address space, it's just memory (at least mostly). Clearly when
> this was implemented, the PGA for each process would use a different
> shared memory segment so there wouldn't be collisions.
> As I mentioned before, I'm sure it was done to use large pages. Since there
> are other mechanisms now, it's no longer necessary, which is why it was
> obsoleted in 10.2.
> Regards,
> Dave
> Roman Podshivalov wrote, On 10/07/08 18:30:
> > David,
> >
> > In my mind ISM is related to shared memory, could it be used for private
> > memory allocation ?
> >
> > thanks
> > --romas

Received on Thu Oct 09 2008 - 11:31:27 CDT

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