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    SubjectRe: Page aging broken in 2.6
    On Sun, Dec 28, 2003 at 12:07:58AM +0100, Roger Luethi wrote:
    > It can matter. Evicting a page that is infrequently referenced by many
    > processes increases the chance that all runnable processes block waiting
    > for that same page later. The likelihood of that happening grows under
    > memory pressure, when "infrequently" may actually be "quite often" and
    > when disk I/O is congested (resulting in higher disk access times).
    > You won't have the same effect when evicting a page that is referenced
    > by one process only, no matter how frequently.

    Part of this is unrealistic; paging I/O being congested must be due to
    paging itself causing seeks without additional I/O load. Reading a
    single page once and then faulting that one page back into numerous
    process address spaces is only one I/O request, and so cannot seek in
    and of itself. So in this scenario, a convoy of processes on a single
    page is plausible; aggravated paging I/O seekiness is not. Did you have
    in mind some additional I/O load? Or do affected processes actually all
    fault before the one I/O completes, and so all block temporarily?

    On Sun, Dec 28, 2003 at 12:07:58AM +0100, Roger Luethi wrote:
    > Having all processes blocked is indeed one problem of 2.6 under memory
    > pressure. I don't know what the cause is, though.

    Can you capture sysrq t while a situation like this is in progress?

    -- wli
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