mm: vmscan: do not count anon pages as reclaimable if swap is small

When swap size is smaller than ram size, not all anon pages can be
written to swap space. So do not count anon pages as reclaimable.
This will increase the slab scan rate under memory pressure.

Change-Id: Ic4fe3c5f3e98e56fad1248f555f916cd75189324
Signed-off-by: Yuanyuan Zhong <zyy@motorola.com>
(cherry picked from commit bc0d09af782178758f17ca23bae8017cbf7dd933)
Reviewed-on: http://gerrit.mot.com/697880


SLTApproved: Slta Waiver <sltawvr@motorola.com>
Tested-by: Jira Key <jirakey@motorola.com>
Reviewed-by: Jeffrey Carlyle <jeff.carlyle@motorola.com>
Submit-Approved: Jira Key <jirakey@motorola.com>