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    SubjectRe: [RFC] respect the referenced bit of KVM guest pages?
    On 08/06/2009 04:06 PM, Wu Fengguang wrote:
    > On Thu, Aug 06, 2009 at 07:44:01PM +0800, Avi Kivity wrote:
    >> On 08/06/2009 01:59 PM, Wu Fengguang wrote:
    > scheme KEEP_MOST:
    >>> How about, for every N pages that you scan, evict at least 1 page,
    >>> regardless of young bit status? That limits overscanning to a N:1
    >>> ratio. With N=250 we'll spend at most 25 usec in order to locate one
    >>> page to evict.
    > scheme DROP_CONTINUOUS:
    >>> This is a quick hack to materialize the idea. It remembers roughly
    >>> the last 32*SWAP_CLUSTER_MAX=1024 active (mapped) pages scanned,
    >>> and if _all of them_ are referenced, then the referenced bit is
    >>> probably meaningless and should not be taken seriously.

    Or one scheme, with N=parameter.

    >> I don't think we should ignore the referenced bit. There could still be
    >> a large batch of unreferenced pages later on that we should
    >> preferentially swap. If we swap at least 1 page for every 250 scanned,
    >> after 4K swaps we will have traversed 1M pages, enough to find them.
    > I guess both schemes have unacceptable flaws.
    > For JVM/BIGMEM workload, most pages would be found referenced _all the time_.
    > So the KEEP_MOST scheme could increase reclaim overheads by N=250 times;
    > while the DROP_CONTINUOUS scheme is effectively zero cost.

    Maybe 250 is an exaggeration. But even with 250, the cost is still
    pretty low compared to the cpu cost of evicting a page (with IPIs and
    tlb flushes).

    error compiling committee.c: too many arguments to function

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      Last update: 2009-08-06 15:45    [W:0.022 / U:0.244 seconds]
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