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    SubjectRe: The performance and behaviour of the anti-fragmentation related patches
    On Mon, Mar 05, 2007 at 09:20:10AM -0600, Joel Schopp wrote:
    > >But if you don't require a lot of higher order allocations anyway, then
    > >guest fragmentation caused by ballooning doesn't seem like much problem.
    > If you only need to allocate 1 page size and smaller allocations then no
    > it's not a problem. As soon as you go above that it will be. You don't
    > need to go all the way up to MAX_ORDER size to see an impact, it's just
    > increasingly more severe as you get away from 1 page and towards MAX_ORDER.

    We allocate order 1 and 2 pages for stuff without too much problem.

    > >If you need higher order allocations, then ballooning is bad because of
    > >fragmentation, so you need memory unplug, so you need higher order
    > >allocations. Goto 1.
    > Yes, it's a closed loop. But hotplug isn't the only one that needs higher
    > order allocations. In fact it's pretty far down the list. I look at it
    > like this, a lot of users need high order allocations for better
    > performance and things like on-demand hugepages. As a bonus you get memory
    > hot-remove.

    on-demand hugepages could be done better anyway by having the hypervisor
    defrag physical memory and provide some way for the guest to ask for a
    hugepage, no?

    > >Balooning probably does skew memory management stats and watermarks, but
    > >that's just because it is implemented as a module. A couple of hooks
    > >should be enough to allow things to be adjusted?
    > That is a good idea independent of the current discussion.

    Well it shouldn't be too difficult. If you cc linux-mm and/or me with
    any thoughts or requirements then I could try to help with it.

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      Last update: 2007-03-05 17:09    [W:0.020 / U:2.608 seconds]
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