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    SubjectRe: clustering page-ins
    On Tue, 20 Jul 1999, Rik van Riel wrote:
    > > as jamie says, it's easy to recognize strict monotonically
    > > increasing sequential access to pages and aggressively read ahead
    > > in that case.
    > OK. Then I guess we want to implement this for mmap() and
    > swap I/O.

    i've implemented a read-ahead algorithm for mmap, and it appears to be
    working pretty well for applications that mmap a file then stream data
    from it (like mpg123). now i have some "implementation detail" questions
    for the list. in no particular order:

    + read-ahead is triggered half a cluster before the end of the
    previously read segment. is this too far in advance?

    + after scheduling the next window, should filemap_nopage run the
    disk queue, like do_generic_file_readahead?

    + should the mmap read-ahead logic reuse the read-ahead context
    contained in the file struct, or should it maintain separate
    context in the vm_area struct?

    + should this logic be overly concerned about protecting the
    read-ahead context from race conditions? a race condition
    is more probable here than in do_generic_file_readahead
    because this code handles shared memory areas.

    + what's a reasonable maximum window size? right now i've set it
    arbitrarily at 256K. would it be worth it to allow up to a megabyte
    per read-ahead? or maybe the maximum value should be parametrized
    to the size of physical memory, just like page_cluster?

    - Chuck Lever
    corporate: <>
    personal: <> or <>

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