Messages in this thread | | | Subject | Re: [PATCH 00/03] Unmapped: Separate unmapped and mapped pages | From | Peter Zijlstra <> | Date | Sat, 11 Mar 2006 22:08:15 +0100 |
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On Fri, 2006-03-10 at 14:38 +0100, Magnus Damm wrote: > On 3/10/06, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> > Breaking the LRU in two like this breaks the page ordering, which makes > > it possible for pages to stay resident even though they have much less > > activity than pages that do get reclaimed. > > Yes, true. But this happens already with a per-zone LRU. LRU pages > that happen to end up in the DMA zone will probably stay there a > longer time than pages in the normal zone. That does not mean it is > right to break the page ordering though, I'm just saying it happens > already and the oldest piece of data in the global system will not be > reclaimed first - instead there are priorities such as unmapped pages > will be reclaimed over mapped and so on. (I strongly feel that there > should be per-node LRU:s, but that's another story)
If reclaim works right* there is equal pressure on each zone (proportional to their size) and hence each page will have an equal life time expectancy.
(*) this is of course not possible for all workloads, however balance_pgdat and the page allocator take pains to make it as true as possible.
Peter
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