mark_page_accessed cannot activate an inactive page that is located on
an inactive LRU pagevec. Hints from filesystems may be ignored as a
result. In preparation for fixing that problem, this patch removes the
per-LRU pagevecs and leaves just one pagevec. The final LRU the page is
added to is deferred until the pagevec is drained.
This means that fewer pagevecs are available and potentially there is
greater contention on the LRU lock. However, this only applies in the case
where there is an almost perfect mix of file, anon, active and inactive
pages being added to the LRU. In practice I expect that we are adding
stream of pages of a particular time and that the changes in contention
will barely be measurable.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>