On Thu, Dec 13, 2012 at 10:34:20AM +0000, Mel Gorman wrote:
> On Wed, Dec 12, 2012 at 04:43:34PM -0500, Johannes Weiner wrote:
> > 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@xxxxxxxxxxx>
>
> 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.
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