)]}'
{
  "commit": "b00949aa2df9970a912bf060bc95e99da356881c",
  "tree": "d86e3942214c20de67a19fd19658c834cc5b5eb3",
  "parents": [
    "8927f66c4ede9a18b4b58f7e6f9debca67065f6b"
  ],
  "author": {
    "name": "Wu Fengguang",
    "email": "fengguang.wu@intel.com",
    "time": "Thu Nov 18 14:38:33 2010 -0600"
  },
  "committer": {
    "name": "Wu Fengguang",
    "email": "fengguang.wu@intel.com",
    "time": "Mon Oct 03 21:08:58 2011 +0800"
  },
  "message": "writeback: per-bdi background threshold\n\nOne thing puzzled me is that in JBOD case, the per-disk writeout\nperformance is smaller than the corresponding single-disk case even\nwhen they have comparable bdi_thresh. Tracing shows find that in single\ndisk case, bdi_writeback is always kept high while in JBOD case, it\ncould drop low from time to time and correspondingly bdi_reclaimable\ncould sometimes rush high.\n\nThe fix is to watch bdi_reclaimable and kick background writeback as\nsoon as it goes high. This resembles the global background threshold\nbut in per-bdi manner. The trick is, as long as bdi_reclaimable does\nnot go high, bdi_writeback naturally won\u0027t go low because\nbdi_reclaimable+bdi_writeback ~\u003d bdi_thresh.\n\nWith less fluctuated writeback pages, JBOD performance is observed to\nincrease noticeably in various cases.\n\nvmstat:nr_written values before/after patch:\n\n  3.1.0-rc4-wo-underrun+      3.1.0-rc4-bgthresh3+  \n------------------------  ------------------------  \n               125596480       +25.9%    158179363  JBOD-10HDD-16G/ext4-100dd-1M-24p-16384M-20:10-X\n                61790815      +110.4%    130032231  JBOD-10HDD-16G/ext4-10dd-1M-24p-16384M-20:10-X\n                58853546        -0.1%     58823828  JBOD-10HDD-16G/ext4-1dd-1M-24p-16384M-20:10-X\n               110159811       +24.7%    137355377  JBOD-10HDD-16G/xfs-100dd-1M-24p-16384M-20:10-X\n                69544762       +10.8%     77080047  JBOD-10HDD-16G/xfs-10dd-1M-24p-16384M-20:10-X\n                50644862        +0.5%     50890006  JBOD-10HDD-16G/xfs-1dd-1M-24p-16384M-20:10-X\n                42677090       +28.0%     54643527  JBOD-10HDD-thresh\u003d100M/ext4-100dd-1M-24p-16384M-100M:10-X\n                47491324       +13.3%     53785605  JBOD-10HDD-thresh\u003d100M/ext4-10dd-1M-24p-16384M-100M:10-X\n                52548986        +0.9%     53001031  JBOD-10HDD-thresh\u003d100M/ext4-1dd-1M-24p-16384M-100M:10-X\n                26783091       +36.8%     36650248  JBOD-10HDD-thresh\u003d100M/xfs-100dd-1M-24p-16384M-100M:10-X\n                35526347       +14.0%     40492312  JBOD-10HDD-thresh\u003d100M/xfs-10dd-1M-24p-16384M-100M:10-X\n                44670723        -1.1%     44177606  JBOD-10HDD-thresh\u003d100M/xfs-1dd-1M-24p-16384M-100M:10-X\n               127996037       +22.4%    156719990  JBOD-10HDD-thresh\u003d2G/ext4-100dd-1M-24p-16384M-2048M:10-X\n                57518856        +3.8%     59677625  JBOD-10HDD-thresh\u003d2G/ext4-10dd-1M-24p-16384M-2048M:10-X\n                51919909       +12.2%     58269894  JBOD-10HDD-thresh\u003d2G/ext4-1dd-1M-24p-16384M-2048M:10-X\n                86410514       +79.0%    154660433  JBOD-10HDD-thresh\u003d2G/xfs-100dd-1M-24p-16384M-2048M:10-X\n                40132519       +38.6%     55617893  JBOD-10HDD-thresh\u003d2G/xfs-10dd-1M-24p-16384M-2048M:10-X\n                48423248        +7.5%     52042927  JBOD-10HDD-thresh\u003d2G/xfs-1dd-1M-24p-16384M-2048M:10-X\n               206041046       +44.1%    296846536  JBOD-10HDD-thresh\u003d4G/xfs-100dd-1M-24p-16384M-4096M:10-X\n                72312903       -19.4%     58272885  JBOD-10HDD-thresh\u003d4G/xfs-10dd-1M-24p-16384M-4096M:10-X\n                50635672        -0.5%     50384787  JBOD-10HDD-thresh\u003d4G/xfs-1dd-1M-24p-16384M-4096M:10-X\n                68308534      +115.7%    147324758  JBOD-10HDD-thresh\u003d800M/ext4-100dd-1M-24p-16384M-800M:10-X\n                57882933       +14.5%     66269621  JBOD-10HDD-thresh\u003d800M/ext4-10dd-1M-24p-16384M-800M:10-X\n                52183472       +12.8%     58855181  JBOD-10HDD-thresh\u003d800M/ext4-1dd-1M-24p-16384M-800M:10-X\n                53788956       +94.2%    104460352  JBOD-10HDD-thresh\u003d800M/xfs-100dd-1M-24p-16384M-800M:10-X\n                44493342       +35.5%     60298210  JBOD-10HDD-thresh\u003d800M/xfs-10dd-1M-24p-16384M-800M:10-X\n                42641209       +18.9%     50681038  JBOD-10HDD-thresh\u003d800M/xfs-1dd-1M-24p-16384M-800M:10-X\n\nSigned-off-by: Wu Fengguang \u003cfengguang.wu@intel.com\u003e\n",
  "tree_diff": [
    {
      "type": "modify",
      "old_id": "28076562ada0d2fc472f716931e9803e027bb400",
      "old_mode": 33188,
      "old_path": "fs/fs-writeback.c",
      "new_id": "6401cd76f109e98ff7cb02e44f661876b4c66a03",
      "new_mode": 33188,
      "new_path": "fs/fs-writeback.c"
    }
  ]
}