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    SubjectRe: [PATCH v4 -mm] make swapin readahead skip over holes
    On Tue, Jan 24, 2012 at 02:14:00PM -0500, Rik van Riel wrote:
    > Ever since abandoning the virtual scan of processes, for scalability
    > reasons, swap space has been a little more fragmented than before.
    > This can lead to the situation where a large memory user is killed,
    > swap space ends up full of "holes" and swapin readahead is totally
    > ineffective.
    >
    > On my home system, after killing a leaky firefox it took over an
    > hour to page just under 2GB of memory back in, slowing the virtual
    > machines down to a crawl.
    >
    > This patch makes swapin readahead simply skip over holes, instead
    > of stopping at them. This allows the system to swap things back in
    > at rates of several MB/second, instead of a few hundred kB/second.
    >
    > The checks done in valid_swaphandles are already done in
    > read_swap_cache_async as well, allowing us to remove a fair amount
    > of code.
    >
    > Signed-off-by: Rik van Riel <riel@redhat.com>

    Acked-by: Johannes Weiner <hannes@cmpxchg.org>


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