Re: [PATCH 1/1] Implement shared page tables

From: Hugh Dickins (hugh_at_veritas.com)
Date: 08/31/05

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    Date:	Wed, 31 Aug 2005 16:06:12 +0100 (BST)
To: "Martin J. Bligh" <mbligh@mbligh.org>

    On Wed, 31 Aug 2005, Martin J. Bligh wrote:
    > --Hugh Dickins <hugh@veritas.com> wrote (on Wednesday, August 31, 2005 14:42:38 +0100):
    > >
    > > Which is indeed a further disincentive against shared page tables.
    >
    > Or shared pagetables a disincentive to randomizing the mmap space ;-)

    Fair point!

    > They're incompatible, but you could be left to choose one or the other
    > via config option.

    Wouldn't need config option: there's /proc/sys/kernel/randomize_va_space
    for the whole running system, compatibility check on the ELFs run, and
    the infinite stack rlimit: enough ways to suppress randomization if it
    doesn't suit you.

    > 3% on "a certain industry-standard database benchmark" (cough) is huge,
    > and we expect the benefit for PPC64 will be larger as we can share the
    > underlying hardware PTEs without TLB flushing as well.

    Okay - and you're implying that 3% comes from _using_ the shared page
    tables, rather than from avoiding the fork/exit overhead of setting
    them up and tearing them down. And it can't use huge TLB pages
    because... fragmentation?

    Hugh
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