Re: Hugepages - benefits / drawbacks
- From: David Miller <David.J.Miller@xxxxxxx>
- To: yong321@xxxxxxxxx
- Date: Fri, 10 Oct 2008 10:22:51 -0500
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.
Regards,
Dave
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
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