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    SubjectRe: Maybe a VM bug in 2.4.18-18 from RH 8.0?
    On Thu, Dec 05, 2002 at 05:34:34PM -0800, Andrew Morton wrote:
    > Andrea Arcangeli wrote:
    > >
    > > ...
    > > He may still suffer other known problems besides
    > > the above two critical highmem fixes (for example if
    > > lower_zone_reserve_ratio is not applied and there's no other fix around
    > > it IMHO, that's generic OS problem not only for linux, and that was my
    > > only sensible solution to fix it, the approch in mainline is way too
    > > weak to make a real difference)
    > argh. I hate that one ;) Giving away 100 megabytes of memory
    > hurts.

    100M hurts on a 4G box? No-way ;)

    it hurts when such 100M of normal zone are mlocked
    by an highmem-capable users and you can't allocate one more inode but
    you have still 3G free of highmem (google is doing this, they even drop
    a check so they can mlock > half of the ram).

    Or it hurts when you can't allocate an inode because such 100M are in
    pagetables on a 64G box and you still have 60G free of highmem.

    > I've never been able to find the workload which makes this
    > necessary. Can you please describe an "exploit" against

    ask google...

    > 2.4.20 which demonstrates the need for this?

    even simpler, swapoff -a and malloc and have fun! ;) (again ask google,
    they run w/o swap for obvious good reasons)

    Or if you have enough time, wait those 100M to be filled by pagetables
    on a 64G box.

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