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    SubjectRe: Fw: FENRIS (nwfs) Source Code Now Available.

    On Mon, 21 Jun 1999, Jeff Merkey wrote:

    > > [...] Also, Windows NT has some pretty nifty stuff
    > > in it's file system architecture for SMP. The way the VM Cache manager is
    > > implemented in Windows NT is nothing short of genius. By caching MCB
    > > allocation run information (NT reads and writes files by constructing MCB
    > > lists in memory, which are in-memory descriptors of a file's contiguous
    > > sector runs), this gives NT the ability to perform some fairly
    > > sophisticated read-ahead and cache predication operations for random
    > > access as well as sequential access files. This architecture is also
    > > superior for SMP operations. MCB lists can basically be sent in a
    > > parallel fashion to the IO subsystem and transacted in parallel. [...]

    would you mind comparing it to what Linux 2.3.7's page cache does? That
    one has pagecache design pretty close to 'genius' as well, and not only on
    paper :) On a 4-ways Xeon we scale read performance ~380%, which is
    basically linear:

    single-process reads done on the same 60k file:

    [root@moon fileben]# ./fileben ./FILE 60000 1 1 1
    READ: 273.76 MB/sec

    4-process read()s done on the same 60k file:

    [root@moon fileben]# ./fileben ./FILE 60000 4 1 1
    READ: 258.16 MB/sec
    READ: 258.09 MB/sec
    READ: 258.04 MB/sec
    READ: 258.20 MB/sec

    part of the rather dramatic speedup is also a new mechanizm: the new
    pagecache now also caches 'filesystem physical block addresses', which
    allows us to skip a costy lookup of filesystem metadata for every block of
    file read() or written.

    -- mingo


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