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

[Hugh Dickins]

On Wed, 31 Aug 2005, Martin J. Bligh wrote:
> --Hugh Dickins <hugh@xxxxxxxxxxx> 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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