Hugh Dickins wrote:

(Whereas the simple vm_swap_full remove_exclusive_swap_page which
Rik added at activate_locked was an order of magnitude more
successful: not a major route, but still worth doing.)

I'm guessing this depends on the workload, too.  With longer
running jobs, we may have more pages staying on the active
list after being swapped out once, while swap fills up with
unrelated things.

Not sure how to trigger that in a benchmark though - it seems
more like a typical week old desktop that has some things
lingering in the swap cache state for days on end...

Why did pagevec_swap_free end up freeing so little?  I guess
because the vm_swap_full remove_exclusive_swap_page in do_swap_page
was successfully freeing so much.  But also, because of another
(incomplete) patch I've had around for months, which I added in
to the instrumentation: when do_wp_page decides it can use the
swapcache page directly, isn't that a very good time to remove
from swapcache?  

That sounds like a good idea.  I wonder if it should be
conditional on vm_swap_full()...

Perhaps Rik can offer some very different results to support
his patch; but if not, I think drop it (and your debug) from
mm for now.

Drop just the swap freeing from the active list rotation,
or also the activate_locked: path (which was effective in
your measurements) ?

-- 
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the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.

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