)]}'
{
  "commit": "3a4c6800f31ea8395628af5e7e490270ee5d0585",
  "tree": "5703cf8140e5b58f5f333dbbf7b1514404584e69",
  "parents": [
    "b578f3fcca1e78624dfb5f358776e63711d7fda2"
  ],
  "author": {
    "name": "Nick Piggin",
    "email": "npiggin@suse.de",
    "time": "Thu Feb 12 04:34:23 2009 +0100"
  },
  "committer": {
    "name": "Linus Torvalds",
    "email": "torvalds@linux-foundation.org",
    "time": "Thu Feb 12 08:10:53 2009 -0800"
  },
  "message": "Fix page writeback thinko, causing Berkeley DB slowdown\n\nA bug was introduced into write_cache_pages cyclic writeout by commit\n31a12666d8f0c22235297e1c1575f82061480029 (\"mm: write_cache_pages cyclic\nfix\").  The intention (and comments) is that we should cycle back and\nlook for more dirty pages at the beginning of the file if there is no\nmore work to be done.\n\nBut the !done condition was dropped from the test.  This means that any\ntime the page writeout loop breaks (eg.  due to nr_to_write \u003d\u003d 0), we\nwill set index to 0, then goto again.  This will set done_index to\nindex, then find done is set, so will proceed to the end of the\nfunction.  When updating mapping-\u003ewriteback_index for cyclic writeout,\nwe now use done_index \u003d\u003d 0, so we\u0027re always cycling back to 0.\n\nThis seemed to be causing random mmap writes (slapadd and iozone) to\nstart writing more pages from the LRU and writeout would slowdown, and\ncaused bugzilla entry\n\n\thttp://bugzilla.kernel.org/show_bug.cgi?id\u003d12604\n\nabout Berkeley DB slowing down dramatically.\n\nWith this patch, iozone random write performance is increased nearly\n5x on my system (iozone -B -r 4k -s 64k -s 512m -s 1200m on ext2).\n\nSigned-off-by: Nick Piggin \u003cnpiggin@suse.de\u003e\nReported-and-tested-by: Jan Kara \u003cjack@suse.cz\u003e\nSigned-off-by: Linus Torvalds \u003ctorvalds@linux-foundation.org\u003e\n",
  "tree_diff": [
    {
      "type": "modify",
      "old_id": "6106a5c7ed44d0f8f134a32d4e21834835e7f4c3",
      "old_mode": 33188,
      "old_path": "mm/page-writeback.c",
      "new_id": "3c84128596ba88892cd1394e334d6c0c5bd12e3d",
      "new_mode": 33188,
      "new_path": "mm/page-writeback.c"
    }
  ]
}