On Thu, 3 Jul 2003, Andrea Arcangeli wrote:

quoted

even if you don't use largepages as you should, the ram cost of the pte
is nothing on 64bit archs, all you care about is to use all the mhz and
tlb entries of the cpu.

On Thu, Jul 03, 2003 at 09:06:32AM -0400, Rik van Riel wrote:

That depends on the number of Oracle processes you have.
Say that page tables need 0.1% of the space of the virtual
space they map.  With 1000 Oracle users you'd end up needing
as much memory in page tables as your shm segment is large.
Of course, in this situation either the application should
use large pages or the kernel should simply reclaim the
page tables (possible while holding the mmap_sem for write).

No, it is not true that pagetable space can be wantonly wasted
on 64-bit.

Try mmap()'ing something sufficiently huge and accessing on average
every PAGE_SIZE'th virtual page, in a single-threaded single process.
e.g. various indexing schemes might do this. This is 1 pagetable page
per page of data (worse if shared), which blows major goats.

There's a reason why those things use inverted pagetables... at any
rate, compacting virtualspace with remap_file_pages() solves it too.

Large pages won't help, since the data isn't contiguous.


-- wli
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