>> >> In many cases, this will stop the box from falling over flat on it's
>> >> face due to ZONE_NORMAL exhaustion (from pte-chains), or even total
>> >> RAM exhaustion (from PTEs). Thus the performance gain is infinite ;-)
>> >
>> > So why has no one written a pte_chain reaper? It is perfectly sane
>> > to allocate a swap entry and move an entire pte_chain to the swap
>> > cache.
>>
>> I think the underlying subsystem does not easily allow for dynamic regeneration,
>> so it's non-trivial.
>
> We swap pages out all of the time in 2.4.x, and that is all I was suggesting
> swap out some but not all of the pages, on a very long pte_chain. And swapping
> out a page is not terribly complex, unless something very drastic has changed.
Right, it's swapping out the controlling structures without swapping
out the pages themselves that's harder.
>> IMHO, it's better not to fill memory with crap in the first place than
>> to invent complex methods of managing and shrinking it afterwards. You
>> only get into pathalogical conditions under sharing situation, else
>> it's limited to about 1% of RAM (bad, but manageable) ... thus providing
>> this sort of sharing nixes the worst of it. Better cache warmth on
>> switches (for TLB misses), faster fork+exec, etc. are nice side-effects.
>
> I will agree with that if everything works so the sharing happens,
> this is a nice feature.
I think it will for most of the situations we run aground with now
(normally 5000 oracle tasks sharing a 2Gb shared segment, or some
such monster).
>> The ultimate solution is per-object reverse mappings, rather than per
>> page, but that's a 2.7 thingy now.
> ???
>
> Last I checked we already had those in 2.4.x, and still in 2.5.x. The
> list of place the address space is mapped.
It's more complicated than that ... I'll let Rik or one of the K42
guys who understand it better than I do explain it (yeah, I'm wimping
out on you ;-))
M.
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This archive was generated by hypermail 2b29 : Wed Oct 23 2002 - 22:00:57 EST