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    SubjectRe: %u-order allocation failed
    > > > Nothing dangeorus there. The -ac vm isnt triggering these cases.
    > >
    > > Sorry, but it can be triggered by _ANY_ VM since buddy allocator was
    > > introduced. You have no guarantee, that you find two or more consecutive
    > > free pages. And if you don't, poll() fails.
    >
    > The two page case isnt one you need to worry about. To all intents and
    > purposes it does not happen,

    How do you know it? I showed a simple case where it may happen.

    > and if you do the maths it isnt going to
    > fail in any interesting ways. Once you go to the 4 page set the odds get
    > a lot longer and then rapidly get very bad indeed,

    I hope you don't want to count probability that the server will or won't
    crash (yes, crash, because when poll in main loop fails, the server
    process has not many choices - it can only terminate itself). This reminds
    me some Microsoft announcement saying that Windows NT are 3 times more
    stable than Windows 95 :-)

    And it does happen - see this:
    http://www.uwsg.indiana.edu/hypermail/linux/kernel/0012.3/0711.html
    Maybe probability was reduced somehow, but the problem is still there.

    Mikulas

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