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    SubjectRe: out_of_memory() heuristic broken for different mem configurations (fwd)

    On Thu, 8 Nov 2001, Marcelo Tosatti wrote:
    > I remember Linus had a reasoning for the "scan _ALL_ ptes until success"
    > behaviour.
    > Linus, was that due to zone-specific (eg DMA shortage on bigmem machine)
    > shortages or ?

    No, the major reason simply _is_ because it's fairly easy to come up with
    test-cases that are mostly MAP_SHARED, and are not out-of-memory.
    Returning early from swap_out() is simply fundamentally wrong - whether we
    have free swap-space or not has very little to do with anything.

    (Well, whether we have free swap space or not _is_ meaningful once we have
    scanned all VM's, but not before that).

    But see my suggestion about potentially noticing the oom _before_ calling
    swap_out(). Thanks to anonymous-in-LRU we have a _lot_ of powerful
    information that we simply traditionally haven't had. It doesn't just tell
    us when we should start swapping out, it can also tell us if swap-out is
    going to need swap-space or not. It can even tell how _much_ swap-space
    we'll need to satisfy the "free N pages from the VM".

    > However, the current code breaks badly as I've tested on the 16GB boxen.

    I understand. I just think the fix needs to be different.


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