)]}'
{
  "commit": "92df3a723f84cdf8133560bbff950a7a99e92bc9",
  "tree": "503efc278236d877508da66ea7ec7cbb81203d64",
  "parents": [
    "f84f6e2b0868f198f97a32ba503d6f9f319a249a"
  ],
  "author": {
    "name": "Mel Gorman",
    "email": "mgorman@suse.de",
    "time": "Mon Oct 31 17:07:56 2011 -0700"
  },
  "committer": {
    "name": "Linus Torvalds",
    "email": "torvalds@linux-foundation.org",
    "time": "Mon Oct 31 17:30:46 2011 -0700"
  },
  "message": "mm: vmscan: throttle reclaim if encountering too many dirty pages under writeback\n\nWorkloads that are allocating frequently and writing files place a large\nnumber of dirty pages on the LRU.  With use-once logic, it is possible for\nthem to reach the end of the LRU quickly requiring the reclaimer to scan\nmore to find clean pages.  Ordinarily, processes that are dirtying memory\nwill get throttled by dirty balancing but this is a global heuristic and\ndoes not take into account that LRUs are maintained on a per-zone basis.\nThis can lead to a situation whereby reclaim is scanning heavily, skipping\nover a large number of pages under writeback and recycling them around the\nLRU consuming CPU.\n\nThis patch checks how many of the number of pages isolated from the LRU\nwere dirty and under writeback.  If a percentage of them under writeback,\nthe process will be throttled if a backing device or the zone is\ncongested.  Note that this applies whether it is anonymous or file-backed\npages that are under writeback meaning that swapping is potentially\nthrottled.  This is intentional due to the fact if the swap device is\ncongested, scanning more pages and dispatching more IO is not going to\nhelp matters.\n\nThe percentage that must be in writeback depends on the priority.  At\ndefault priority, all of them must be dirty.  At DEF_PRIORITY-1, 50% of\nthem must be, DEF_PRIORITY-2, 25% etc.  i.e.  as pressure increases the\ngreater the likelihood the process will get throttled to allow the flusher\nthreads to make some progress.\n\nSigned-off-by: Mel Gorman \u003cmgorman@suse.de\u003e\nReviewed-by: Minchan Kim \u003cminchan.kim@gmail.com\u003e\nAcked-by: Johannes Weiner \u003cjweiner@redhat.com\u003e\nCc: Dave Chinner \u003cdavid@fromorbit.com\u003e\nCc: Christoph Hellwig \u003chch@infradead.org\u003e\nCc: Wu Fengguang \u003cfengguang.wu@intel.com\u003e\nCc: Jan Kara \u003cjack@suse.cz\u003e\nCc: Rik van Riel \u003criel@redhat.com\u003e\nCc: Mel Gorman \u003cmgorman@suse.de\u003e\nCc: Alex Elder \u003caelder@sgi.com\u003e\nCc: Theodore Ts\u0027o \u003ctytso@mit.edu\u003e\nCc: Chris Mason \u003cchris.mason@oracle.com\u003e\nCc: Dave Hansen \u003cdave@linux.vnet.ibm.com\u003e\nSigned-off-by: Andrew Morton \u003cakpm@linux-foundation.org\u003e\nSigned-off-by: Linus Torvalds \u003ctorvalds@linux-foundation.org\u003e\n",
  "tree_diff": [
    {
      "type": "modify",
      "old_id": "15e3a29fdb234c20480a6438e8861834346e88fc",
      "old_mode": 33188,
      "old_path": "mm/vmscan.c",
      "new_id": "7b0573f33a27a0b47c9e11277394a5b8284c275b",
      "new_mode": 33188,
      "new_path": "mm/vmscan.c"
    }
  ]
}