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    SubjectRe: [RFC, PATCH] Slab counter troubles with swap prefetch?
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    On Fri, 11 Nov 2005 10:13, Christoph Lameter wrote:
    > On Fri, 11 Nov 2005, Con Kolivas wrote:
    > > > This patch splits the counter into the nr_local_slab which reflects
    > > > slab pages allocated from the local zones (and this number is useful
    > > > at least as a guidance for the VM) and the remotely allocated pages.
    > >
    > > How large a contribution is the remote slab size likely to be? Would this
    > > information be useful to anyone potentially in future code besides swap
    > > prefetch? The nature of prefetch is that this is only a fairly coarse
    > > measure of how full the vm is with data we don't want to displace. Thus
    > > it is also not important that it is very accurate.
    >
    > The size of the remote cache depends on many factors. The application can
    > influence that by setting memory policies.
    >
    > > Unless the remote slab size can be a very large contribution, or having
    > > local
    >
    > Yes it can be quite large. On some of my tests with applications these are
    > 100%. This is typical if the application sets the policy in such a way
    > that all allocations are off node or if the kernel has to allocate memory
    > on a certain node for a device.

    Great. Thanks for the information, and I prefer to see this patch in on that
    basis.

    > > As a side note I doubt any serious size numa hardware will ever be idle
    > > enough by swap prefetch standards to even start prefetching swap pages.
    > > If you think hardware of this sort is likely to benefit from swap
    > > prefetch then perhaps we should look at relaxing the conditions under
    > > which prefetching occurs.
    >
    > Small scale NUMA machines may benefit from swap prefetch but on larger
    > machines people usually try to avoid swap altogether.

    Then I won't alter the when-to-prefetch algorithm.

    Thanks!
    Con
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