nfs: writeback pages wait queue

The generic writeback routines are departing from congestion_wait()
in preference of get_request_wait(), aka. waiting on the block queues.

Introduce the missing writeback wait queue for NFS, otherwise its
writeback pages will grow greedily, exhausting all PG_dirty pages.

Tests show that it can effectively reduce stalls in the disk-network
pipeline, improve performance and reduce delays.

The test cases are basically

	for run in 1 2 3
	for nr_dd in 1 10 100
	for dirty_thresh in 10M 100M 1000M 2G
		start $nr_dd dd's writing to a 1-disk mem=12G NFS server

During all tests, nfs_congestion_kb is set to 1/8 dirty_thresh.

    3.2.0-rc1    3.2.0-rc1-ioless-full+
  (w/o patch)                (w/ patch)
  -----------  ------------------------
        20.66      +136.7%        48.90  thresh=1000M/nfs-100dd-1
        20.82      +147.5%        51.52  thresh=1000M/nfs-100dd-2
        20.57      +129.8%        47.26  thresh=1000M/nfs-100dd-3
        35.96       +96.5%        70.67  thresh=1000M/nfs-10dd-1
        37.47       +89.1%        70.85  thresh=1000M/nfs-10dd-2
        34.55      +106.1%        71.21  thresh=1000M/nfs-10dd-3
        58.24       +28.2%        74.63  thresh=1000M/nfs-1dd-1
        59.83       +18.6%        70.93  thresh=1000M/nfs-1dd-2
        58.30       +31.4%        76.61  thresh=1000M/nfs-1dd-3
        23.69       -10.0%        21.33  thresh=100M/nfs-100dd-1
        23.59        -1.7%        23.19  thresh=100M/nfs-100dd-2
        23.94        -1.0%        23.70  thresh=100M/nfs-100dd-3
        27.06        -0.0%        27.06  thresh=100M/nfs-10dd-1
        25.43        +4.8%        26.66  thresh=100M/nfs-10dd-2
        27.21        -0.8%        26.99  thresh=100M/nfs-10dd-3
        53.82        +4.4%        56.17  thresh=100M/nfs-1dd-1
        55.80        +4.2%        58.12  thresh=100M/nfs-1dd-2
        55.75        +2.9%        57.37  thresh=100M/nfs-1dd-3
        15.47        +1.3%        15.68  thresh=10M/nfs-10dd-1
        16.09        -3.5%        15.53  thresh=10M/nfs-10dd-2
        15.09        -0.9%        14.96  thresh=10M/nfs-10dd-3
        26.65       +13.0%        30.10  thresh=10M/nfs-1dd-1
        25.09        +7.7%        27.02  thresh=10M/nfs-1dd-2
        27.16        +3.3%        28.06  thresh=10M/nfs-1dd-3
        27.51       +78.6%        49.11  thresh=2G/nfs-100dd-1
        22.46      +131.6%        52.01  thresh=2G/nfs-100dd-2
        12.95      +289.8%        50.50  thresh=2G/nfs-100dd-3
        42.28       +81.0%        76.52  thresh=2G/nfs-10dd-1
        40.33       +78.8%        72.10  thresh=2G/nfs-10dd-2
        42.52       +67.6%        71.27  thresh=2G/nfs-10dd-3
        62.27       +34.6%        83.84  thresh=2G/nfs-1dd-1
        60.10       +35.6%        81.48  thresh=2G/nfs-1dd-2
        66.29       +17.5%        77.88  thresh=2G/nfs-1dd-3
      1164.97       +41.6%      1649.19  TOTAL write_bw

The local queue time for WRITE RPCs could be reduced by several orders!

    3.2.0-rc1    3.2.0-rc1-ioless-full+
  -----------  ------------------------
     90226.82       -99.9%        92.07  thresh=1000M/nfs-100dd-1
     88904.27       -99.9%        80.21  thresh=1000M/nfs-100dd-2
     97436.73       -99.9%        87.32  thresh=1000M/nfs-100dd-3
     62167.19       -99.3%       444.25  thresh=1000M/nfs-10dd-1
     64150.34       -99.2%       539.38  thresh=1000M/nfs-10dd-2
     78675.54       -99.3%       540.27  thresh=1000M/nfs-10dd-3
      5372.84       +57.8%      8477.45  thresh=1000M/nfs-1dd-1
     10245.66       -51.2%      4995.71  thresh=1000M/nfs-1dd-2
      4744.06      +109.1%      9919.55  thresh=1000M/nfs-1dd-3
      1727.29        -9.6%      1562.16  thresh=100M/nfs-100dd-1
      2183.49        +4.4%      2280.21  thresh=100M/nfs-100dd-2
      2201.49        +3.7%      2281.92  thresh=100M/nfs-100dd-3
      6213.73       +19.9%      7448.13  thresh=100M/nfs-10dd-1
      8127.01        +3.2%      8387.06  thresh=100M/nfs-10dd-2
      7255.35        +4.4%      7571.11  thresh=100M/nfs-10dd-3
      1144.67       +20.4%      1378.01  thresh=100M/nfs-1dd-1
      1010.02       +19.0%      1202.22  thresh=100M/nfs-1dd-2
       906.33       +15.8%      1049.76  thresh=100M/nfs-1dd-3
       642.82       +17.3%       753.80  thresh=10M/nfs-10dd-1
       766.82       -21.7%       600.18  thresh=10M/nfs-10dd-2
       575.95       +16.5%       670.85  thresh=10M/nfs-10dd-3
        21.91       +71.0%        37.47  thresh=10M/nfs-1dd-1
        16.70      +105.3%        34.29  thresh=10M/nfs-1dd-2
        19.05       -71.3%         5.47  thresh=10M/nfs-1dd-3
    123877.11       -99.0%      1187.27  thresh=2G/nfs-100dd-1
    122353.65       -98.8%      1505.84  thresh=2G/nfs-100dd-2
    101140.82       -98.4%      1641.03  thresh=2G/nfs-100dd-3
     78248.51       -98.9%       892.00  thresh=2G/nfs-10dd-1
     84589.42       -98.6%      1212.17  thresh=2G/nfs-10dd-2
     89684.95       -99.4%       495.28  thresh=2G/nfs-10dd-3
     10405.39        -6.9%      9684.57  thresh=2G/nfs-1dd-1
     16151.86       -48.5%      8316.69  thresh=2G/nfs-1dd-2
     16119.17       -49.0%      8214.84  thresh=2G/nfs-1dd-3
   1177306.98       -92.1%     93588.50  TOTAL nfs_write_queue_time

The average COMMIT size is not impacted too much.

    3.2.0-rc1    3.2.0-rc1-ioless-full+
  -----------  ------------------------
         5.56       +44.9%         8.06  thresh=1000M/nfs-100dd-1
         4.14      +109.1%         8.67  thresh=1000M/nfs-100dd-2
         5.46       +16.3%         6.35  thresh=1000M/nfs-100dd-3
        52.04        -8.4%        47.70  thresh=1000M/nfs-10dd-1
        52.33       -13.8%        45.09  thresh=1000M/nfs-10dd-2
        51.72        -9.2%        46.98  thresh=1000M/nfs-10dd-3
       484.63        -8.6%       443.16  thresh=1000M/nfs-1dd-1
       492.42        -8.2%       452.26  thresh=1000M/nfs-1dd-2
       493.13       -11.4%       437.15  thresh=1000M/nfs-1dd-3
        32.52       -72.9%         8.80  thresh=100M/nfs-100dd-1
        36.15       +26.1%        45.58  thresh=100M/nfs-100dd-2
        38.33        +0.4%        38.49  thresh=100M/nfs-100dd-3
         5.67        +0.5%         5.69  thresh=100M/nfs-10dd-1
         5.74        -1.1%         5.68  thresh=100M/nfs-10dd-2
         5.69        +0.9%         5.74  thresh=100M/nfs-10dd-3
        44.91        -1.0%        44.45  thresh=100M/nfs-1dd-1
        44.22        -0.6%        43.96  thresh=100M/nfs-1dd-2
        44.18        +0.2%        44.28  thresh=100M/nfs-1dd-3
         1.42        +1.1%         1.43  thresh=10M/nfs-10dd-1
         1.48        +0.3%         1.48  thresh=10M/nfs-10dd-2
         1.43        -1.0%         1.42  thresh=10M/nfs-10dd-3
         5.51        -6.8%         5.14  thresh=10M/nfs-1dd-1
         5.91        -8.1%         5.43  thresh=10M/nfs-1dd-2
         5.44        +3.0%         5.61  thresh=10M/nfs-1dd-3
         8.80        +6.6%         9.38  thresh=2G/nfs-100dd-1
         8.51       +65.2%        14.06  thresh=2G/nfs-100dd-2
        15.28       -13.2%        13.27  thresh=2G/nfs-100dd-3
       105.12       -24.9%        78.99  thresh=2G/nfs-10dd-1
       101.90        -9.1%        92.60  thresh=2G/nfs-10dd-2
       106.24       -29.7%        74.65  thresh=2G/nfs-10dd-3
       909.85        +0.4%       913.68  thresh=2G/nfs-1dd-1
      1030.45       -18.3%       841.68  thresh=2G/nfs-1dd-2
      1016.56       -11.6%       898.36  thresh=2G/nfs-1dd-3
      5222.74       -10.1%      4695.25  TOTAL nfs_commit_size

And here is the list of overall numbers.

    3.2.0-rc1    3.2.0-rc1-ioless-full+
  -----------  ------------------------
      1164.97       +41.6%      1649.19  TOTAL write_bw
     54799.00       +25.0%     68500.00  TOTAL nfs_nr_commits
   3543263.00        -3.3%   3425418.00  TOTAL nfs_nr_writes
      5222.74       -10.1%      4695.25  TOTAL nfs_commit_size
         7.62       +89.2%        14.42  TOTAL nfs_write_size
   1177306.98       -92.1%     93588.50  TOTAL nfs_write_queue_time
      5977.02       -16.0%      5019.34  TOTAL nfs_write_rtt_time
   1183360.15       -91.7%     98645.74  TOTAL nfs_write_execute_time
     51186.59       -62.5%     19170.98  TOTAL nfs_commit_queue_time
     81801.14        +3.6%     84735.19  TOTAL nfs_commit_rtt_time
    133015.32       -21.9%    103926.05  TOTAL nfs_commit_execute_time

Feng: do more coarse grained throttle on each ->writepages rather than
on each page, for better performance and avoid throttled-before-send-rpc
deadlock

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

Conflicts:
	fs/nfs/write.c
vmscan: move referenced VM_EXEC pages to active list

In commit 64574746, "vmscan: detect mapped file pages used only once",
Johannes Weiner, added logic to page_check_reference to cycle again
used once pages.

In commit 8cab4754, "vmscan: make mapped executable pages the first
class citizen", Wu Fengguang, added logic to shrink_active_list which
protects file-backed VM_EXEC pages by keeping them in the active_list if
they are referenced.

This patch adds logic to move such pages from the inactive list to the
active list immediately if they have been referenced. If a VM_EXEC page
is seen as referenced during an inactive list scan, that reference must
have occurred after the page was put on the inactive list. There is no
need to wait for the page to be referenced again.

Change-Id: I17c312e916377e93e5a92c52518b6c829f9ab30b
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>