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    SubjectRe: Results: pre6 vs pre6+zlatko's_patch vs pre5 vs arcavm13
    On Sat, 9 Jan 1999, Linus Torvalds wrote:

    > Can you run pre6+zlatko with just the mm/page_alloc.c one-liner reverted
    > to pre5? That is, take pre6+zlatko, and just change

    I have no time to try code these days :(

    > try_to_free_pages(gfp_mask, freepages.high - nr_free_pages);
    > back to
    > try_to_free_pages(gfp_mask, SWAP_CLUSTER_MAX);
    > That particular one-liner was almost certainly a mistake, it was done on
    > the mistaken assumption that the clustering problem was due to
    > insufficient write-time clustering - while zlatko found that it was
    > actually due to fragmentation in the swap area. With zlatkos patch, the
    > original SWAP_CLUSTER_MAX is probably better and almost certainly results
    > in smoother behaviour due to less extreme free_pages..

    I don't know which is zlatkos patch but my point is that it's
    try_to_free_pages that has to care to be balanced and to do things at
    best. I want to be allowed to ask try_to_free_pages to free any kind of
    space and such function has to run _always_ efficient.

    My current free_user_and_cache() (arca-vm-13) is bad because it doesn't
    swapout aggressively. I am fixing it right now. When I'll have finished
    I'll post the new patch.

    BTW, the reason pre6 is slower than my current _bad_ free_user_and_cache()
    (arca-vm-13) in low memory machines is that in high memory machines the
    freepages.min is something like 255 while in low memory machines
    freepages.min it's close to SWAP_CUSTER_MAX. So in low memory machines the
    swapout cluster has to be reduced (because now swapout doesn't free
    pages). free_user_and_cache() has to care about these issues and I see
    plain wrong to hardwire the swap cluster size to a constant number since
    the freepages values are dynamic (and also changable via sysctl).

    I am not sure of all this, but this is currently my thought.


    Andrea Arcangeli

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