On Thu, Dec 13, 2012 at 02:05:34PM -0500, Johannes Weiner wrote:

On Thu, Dec 13, 2012 at 10:34:20AM +0000, Mel Gorman wrote:

quoted

On Wed, Dec 12, 2012 at 04:43:34PM -0500, Johannes Weiner wrote:

quoted

When a reclaim scanner is doing its final scan before giving up and
there is swap space available, pay no attention to swappiness
preference anymore.  Just swap.

Note that this change won't make too big of a difference for general
reclaim: anonymous pages are already force-scanned when there is only
very little file cache left, and there very likely isn't when the
reclaimer enters this final cycle.

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

Ok, I see the motivation for your patch but is the block inside still
wrong for what you want? After your patch the block looks like this

                if (sc->priority || noswap) {
                        scan >>= sc->priority;
                        if (!scan && force_scan)
                                scan = SWAP_CLUSTER_MAX;
                        scan = div64_u64(scan * fraction[file], denominator);
                }

if sc->priority == 0 and swappiness==0 then you enter this block but
fraction[0] for anonymous pages will also be 0 and because of the ordering
of statements there, scan will be

scan = scan * 0 / denominator

so you are still not reclaiming anonymous pages in the swappiness=0
case. What did I miss?

Don't get confused by noswap, it is only set when there physically is
no swap space.  If !sc->priority, that block is skipped and
fraction[0] does not matter.

/me slaps self

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

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