Messages in this thread | | | Date | Tue, 22 Oct 2002 10:36:40 -0700 | From | "Martin J. Bligh" <> | Subject | Re: [PATCH 2.5.43-mm2] New shared page table patch |
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>> > 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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