Messages in this thread | | | Date | Fri, 27 Jun 2003 07:43:50 -0700 | From | "Martin J. Bligh" <> | Subject | Re: [RFC] My research agenda for 2.7 |
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>> > I also wonder if moving kernel pages is really worth the hassle. >> >> That's the question of course. The benefit is getting rid of high order >> allocation failures, and gaining some confidence that larger filesystem >> blocksizes will work reliably, however the workload evolves.
Oh, BTW ... I suspect you've realised this already, but ....
The buddy allocator is not a good system for getting rid of fragmentation. If I group pages together in aligned pairs, and F is free and A is allocated, it'll not do anything useful with this:
F A A F F A A F F A A F F A A F F A F A
because the adjacent "F"s aren't "buddies". It seems that the purpose of the buddy allocator was to be quick at allocating pages. Now that we stuck a front end cache on it, in the form of hot & cold pages, that goal no longer seems paramount - altering it to reduce fragmentation at the source, rather than actively defrag afterwards would seem like a good goal to me.
M.
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