Messages in this thread | | | From | David Mosberger <> | Date | Sat, 3 Aug 2002 14:18:15 -0700 | Subject | Re: large page patch (fwd) (fwd) |
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>>>>> On Sat, 3 Aug 2002 12:43:47 -0700 (PDT), Linus Torvalds <torvalds@transmeta.com> said:
>> You don't need separate system calls for that: with a transparent >> superpage framework and a privileged & reserved giant-page pool, >> it's trivial to set up things such that your favorite data base >> will always be able to get the giant pages (and hence the giant >> TLB mappings) it wants. The only thing you lose in the >> transparent case is control over _which_ pages need to use the >> pinned giant pages. I can certainly imagine cases where this >> would be an issue, but I kind of doubt it would be an issue for >> databases.
Linus> That's _probably_ true. There aren't that many allocations Linus> that ask for megabytes of consecutive memory that wouldn't Linus> want to do it. However, there might certainly be non-critical Linus> maintenance programs (with the same privileges as the Linus> database program proper) that _do_ do large allocations, and Linus> that we don't want to give large pages to.
Linus> Guessing is always bad, especially since the application Linus> certainly does know what it wants.
Yes, but that applies even to a transparent superpage scheme: in those instances where an application knows what page size is optimal, it's better if the application can express that (saves time promoting/demoting pages needlessly). It's not unlike madvise() or the readahead() syscall: use reasonable policies for the ordinary apps, and provide the means to let the smart apps tell the kernel exactly what they need.
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