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    SubjectRe: [patch 10/21] buffer heads: Support slab defrag
    On Mon, May 19, 2008 at 09:44:11AM -0700, Christoph Lameter wrote:
    > On Mon, 19 May 2008, David Chinner wrote:
    > > Defragmentation is triggered as part of the usual memory reclaim
    > > process. Which implies we've run out of free memory, correct?
    > Yes but we have already reclaimed some memory.
    > > > How do you trigger such a special writeout?
    > >
    > > filemap_fdatawrite_range() perhaps?
    > Could you provide me such a patch? I would not know how much to writeout.
    > If we had such a method then we could also use that for the swap case
    > where we also write out single pages?

    How hard is it? I don't have time right now to do this, but it's essentially:

    mapping = page->mapping;
    - mapping->aops->writepage();
    + filemap_fdatawrite_range(mapping, start, end);

    Where [start,end] span page->index and are is large enough
    to get a substantial sized I/O to disk (say at least SWAP_CLUSTER_MAX
    pages, preferrably larger for 4k page size machines).


    Dave Chinner
    Principal Engineer
    SGI Australian Software Group

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