>> > I think it will for most of the situations we run aground with now
>> > (normally 5000 oracle tasks sharing a 2Gb shared segment, or some
>> > such monster).
>>
>> 10 GB pagetable overhead, for 2 GB of data. No customer I
>> know would accept that much OS overhead.
>>
>> To reduce the overhead we could either reclaim the page
>> tables and reconstruct them when needed (lots of work) or
>> we could share the page tables (less runtime overhead).
>
> Or you use 4MB pages. That tends to work much better and has less
> complexity. Shared page tables don't work well on x86 when you have
> a database trying to access an SGA larger than the virtual address
> space, as each process tends to map its own window into the buffer
> pool. Highmem with 32 bit va just plain sucks. The right answer is
> to change the architecture of the application to not run with 5000
> unique processes.
Bear in mind that large pages are neither swap backed or file backed
(vetoed by Linus), for starters. There are other large app problem scenarios
apart from Oracle ;-)
M.
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This archive was generated by hypermail 2b29 : Wed Oct 23 2002 - 22:00:59 EST