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 <redacted>

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

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