[v4][PATCH 0/6] mm: vmscan: Batch page reclamation under shink_page_list

[Dave Hansen]

These are an update of Tim Chen's earlier work:

	http://lkml.kernel.org/r/1347293960.9977.70.camel@schen9-DESK

I broke the patches up a bit more, and tried to incorporate some
changes based on some feedback from Mel and Andrew.

Changes for v4:
 * generated on top of linux-next-20130530, plus Mel's vmscan
   fixes:
	http://lkml.kernel.org/r/1369659778-6772-2-git-send-email-mgorman@xxxxxxx
 * added some proper vmscan/swap: prefixes to the subjects

Changes for v3:
 * Add batch draining before congestion_wait()
 * minor merge conflicts with Mel's vmscan work

Changes for v2:
 * use page_mapping() accessor instead of direct access
   to page->mapping (could cause crashes when running in
   to swap cache pages.
 * group the batch function's introduction patch with
   its first use
 * rename a few functions as suggested by Mel
 * Ran some single-threaded tests to look for regressions
   caused by the batching.  If there is overhead, it is only
   in the worst-case scenarios, and then only in hundreths of
   a percent of CPU time.

If you're curious how effective the batching is, I have a quick
and dirty patch to keep some stats:

	https://www.sr71.net/~dave/intel/rmb-stats-only.patch

--

To do page reclamation in shrink_page_list function, there are
two locks taken on a page by page basis.  One is the tree lock
protecting the radix tree of the page mapping and the other is
the mapping->i_mmap_mutex protecting the mapped pages.  This set
deals only with mapping->tree_lock.

Tim managed to get 14% throughput improvement when with a workload
putting heavy pressure of page cache by reading many large mmaped
files simultaneously on a 8 socket Westmere server.

I've been testing these by running large parallel kernel compiles
on systems that are under memory pressure.  During development,
I caught quite a few races on smaller setups, and it's being
quite stable that large (160 logical CPU / 1TB) system.
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