Re: Hugepages - benefits / drawbacks

From: David Miller <David.J.Miller_at_Sun.COM>
Date: Fri, 10 Oct 2008 10:22:51 -0500
Message-id: <48EF734B.7030306@Sun.COM>

Hi Yong,

To clarify a bit further, ISM pages do NOT have to be large pages. And large pages do NOT have to be ISM pages. Before Solaris 9, only ISM pages could be large pages. With Solaris 9 we started adding large page support for other kinds of memory, but manually only (see "man ppgsz" for some details). With Solaris 10, large pages became default for certain kinds of memory. Every update of Solaris 10 (and Update 6 will be out soon) has increased the different kinds of memory that use large pages by default.

As opposed to Linux HugePages (at least as I understand them), Solaris large pages are available in the system automatically. Large pages are broken into smaller ones automatically as the need arises. And large pages are reconstructed from smaller ones if possible as the need arises as well.

The term "_use_ism_for_pga" was used because at that time only ISM pages could be large pages. I agree it is confusing, especially now.



Yong Huang wrote, On 10/09/08 11:31:
> 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

Received on Fri Oct 10 2008 - 10:22:51 CDT

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