Messages in this thread | | | Date | Mon, 21 Oct 2002 22:55:57 -0700 | From | "Martin J. Bligh" <> | Subject | Re: [PATCH 2.5.43-mm2] New shared page table patch |
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>> >> 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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