On 12/14/2012 03:37 AM, Michal Hocko wrote:

I can answer the later. Because memsw comes with its price and
swappiness is much cheaper. On the other hand it makes sense that
swappiness==0 doesn't swap at all. Or do you think we should get back to
_almost_ doesn't swap at all?

swappiness==0 will swap in emergencies, specifically when we have
almost no page cache left, we will still swap things out:

         if (global_reclaim(sc)) {
                 free  = zone_page_state(zone, NR_FREE_PAGES);
                 if (unlikely(file + free <= high_wmark_pages(zone))) {
                         /*
                          * If we have very few page cache pages, force-scan
                          * anon pages.
                          */
                         fraction[0] = 1;
                         fraction[1] = 0;
                         denominator = 1;
                         goto out;

This makes sense, because people who set swappiness==0 but
do have swap space available would probably prefer some
emergency swapping over an OOM kill.

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