Oracle memory allocation on Linux 2.6

Hi all,

With the latest Linux kernels, things have gotten hard to tune
regarding the SGA/PGA we can allocate. I'm mainly talking about the
physical memory that is allocated to the OS buffers/caches to make
full use of the memory. With earlier kernels, we had vm.pagecache to
control easily these amounts of memory. Now there is vm.swapiness with
the unfathomable algorithm behind it (read: AFAIK we cannot really
control the OS buffers/caches anymore.)

Moreover, SGA locking is not possible (or rather not advised by Oracle
support) and it is really difficult to check how much physical memory
our SGA is actually using. Even with vm.swapiness=0, huge amounts of
OS buffers/caches get allocated with the obvious conclusion that
"inactive" SGA blocks are paged out to disk, with at least two cons:
this unwanted paging activity (even if it is limited) and the fact
that calculating the "free" physical memory on our box we could
allocate to the PGA/SGA (or other applications) without major paging
is almost impossible.

Any advice in this regard from your experience with Linux 2.6 (and any
Oracle version)?

TIA,
Jerome
.

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