Messages in this thread | | | From | David Mosberger <> | Date | Fri, 2 Aug 2002 20:19:59 -0700 | Subject | Re: large page patch (fwd) (fwd) |
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>>>>> On Fri, 2 Aug 2002 12:34:08 -0700 (PDT), Linus Torvalds <torvalds@transmeta.com> said:
Linus> We may well expand the FS layer to bigger pages, but "bigger" Linus> is almost certainly not going to include things like 256MB Linus> pages - if for no other reason than the fact that memory Linus> fragmentation really means that the limit on page sizes in Linus> practice is somewhere around 128kB for any reasonable usage Linus> patterns even with gigabytes of RAM.
Linus> And _maybe_ we might get to the single-digit megabytes. I Linus> doubt it, simply because even with a good buddy allocator and Linus> a memory manager that actively frees pages to get large Linus> contiguous chunks of RAM, it's basically impossible to have Linus> something that can reliably give you that big chunks without Linus> making normal performance go totally down the toiled.
The Rice people avoided some of the fragmentation problems by pro-actively allocating a max-order physical page, even when only a (small) virtual page was being mapped. This should work very well as long as the total memory usage (including memory lost due to internal fragmentation of max-order physical pages) doesn't exceed available memory. That's not a condition which will hold for every system in the world, but I suspect it is true for lots of systems for large periods of time. And since superpages quickly become counter-productive in tight-memory situations anyhow, this seems like a very reasonable approach.
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