Long time spent in swap_out &co

["John Fremlin" <vii@penguinpowered.com>]

I had a look at vmscan.c and noticed that the swap_out process
selection procedure looks suboptimal (this is 2.4.0-test1-ac7 with
Rik's mm patch rev 3). If I make a mistake, please correct it gently
(I am a clueless newbie).

        (a) The entire list of processes is scanned through each time
        at least once. (Slow, and holding a lock.)

        (b) The biggest rss is chosen. Admittedly the swap_cnt
        heuristics help a bit but it means that a large process that
        is on touching its pages will keep distracting attention from
        more smaller processes that may or may not be more wasteful.

Suggestions

        Guess a reasonable minimum size process to look at (say, twice
        the average of the first couple of size_cnts) so the entire
        list isn't scanned through so often and different processes
        will be targeted first when all the size_cnts are reset.

        Are we just dealing with the running processes? (If not, why
        not first try to swap out the sleeping ones?)

        Or, target processes with fewest page faults.

        [I'm basically unconvinced of the idea of size_cnt]

Hard evidence

        I set up a lot of processes to run, more than my box can
        handle and a large proportion of SysReq-Ps had EIPs in
        swap_out. (Waiting for lock? Not checked).

-- 

	http://altern.org/vii
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