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    SubjectRe: What to expect with the 2.6 VM
    On Thu, 3 Jul 2003, Andrea Arcangeli wrote:
    >> 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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