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    SubjectRe: Possible Idea with filesystem buffering.

    On Tuesday, January 22, 2002 11:32:09 PM +0300 Hans Reiser
    <> wrote:

    >> Its not about the cost of a function call, it's what the FS does to make
    >> that call useful. Pretend for a second the VM tells the FS everything it
    >> needs to know to age a page (whatever scheme the FS wants to use).
    >> Then pretend the VM decides there's memory pressure, and tells the FS
    >> subcache to start freeing ram. So, the FS goes through its list of pages
    >> and finds the most suitable one for flushing, but it has no idea how
    >> suitable that page is in comparison with the pages that don't belong to
    >> that FS (or even other pages from different mount points of the same FS
    >> flavor).
    > Why does it need to know how suitable it is compared to the other
    > subcaches? It just ages X pages, and depends on the VM to determine how
    > large X is. The VM pressures subcaches in proportion to their size, it
    > doesn't need to know how suitable one page is compared to another, it
    > just has a notion of push on everyone in proportion to their size.

    If subcache A has 1000 pages that are very very active, and subcache B has
    500 pages that never ever get used, should A get twice as much memory
    pressure? That's what we want to avoid, and I don't see how subcaches
    allow it.


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