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Date: Fri, 14 Dec 2007 21:18:14 +0530 From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> To: cmm@...ibm.com, tytso@....edu Cc: linux-ext4@...r.kernel.org Subject: [RFC] truncate_mutex to read_write semaphore The series include the truncate_mutex to read write semaphore conversion. I am marking below some of the test results. For O_DIRECT workloads we won't see the contention on truncate mutex because we are doing a get_block under inode->i_mutex. For FIBMAP we won't see contention because the get_block get called under BKL. threaded read with low memory --------------------------- Top contenting locks were: (/proc/lock_stat output) &q->__queue_lock: 12549 12572 10.65 3302.16 36818.78 46618 395721 3.47 49636.48 571453.47 &inode->i_data.tree_lock-W: 3970 4026 2.62 33.39 3508.74 25924 95164 5.33 949.59 80180.03 &inode->i_data.tree_lock-R: 1937 2002 2.52 22.05 1528.78 19543 141863 5.57 119.72 137126.60 &ei->truncate_mutex#2: 4553 4769 169.62 1028484.20 39334253.92 19610 47069 31.74 102280.63 680802.57 second run --------- &q->__queue_lock: 12499 12535 3.76 247.71 19799.94 46341 405427 4.34 216.31 527282.59 &inode->i_data.tree_lock-W: 4009 4071 10.04 31.78 3434.95 25612 93458 7.29 61.87 78365.20 &inode->i_data.tree_lock-R: 1919 1973 4.43 30.93 1523.04 18953 142635 4.95 109.20 137098.84 &ei->truncate_mutex#2: 4346 4499 1546.39 896379.29 31107317.47 19051 48223 37.94 122579.25 628968.65 The above result implies that the threaded read with low memory (booted with mem=512M on a 16 cpu x86-64) results in contention on truncate_mutex. threaded read with low memory after converting to i_data_sem --------------- &ei->i_data_sem-R: 0 0 0.00 0.00 0.00 18017 48801 38.12 3494783.37 22982474.21 &ei->i_data_sem-R: 0 0 0.00 0.00 0.00 18233 49118 45.09 4953783.87 32699001.46 As you can see from the /proc/lock_stat output above the write semaphore is not taken at all. threaded write -------------- &ei->i_data_sem-W: 0 0 0.00 0.00 0.00 24 64163 41.04 2620905.32 16331786.48 &ei->i_data_sem-R: 0 0 0.00 0.00 0.00 13352 83969 51.40 1212864.74 2834511.75 Here we see some read semphore acquisition. We take read mode of the semaphore to not content in the overwrite case. We see no contention here because the write gets done under inode->i_mutex &sb->s_type->i_mutex_key#1: 313958 313962 3650.35 99510834.17 4881402594.11 314481 616528 37.22 7579553.97 54139119.82 -------------------------- &sb->s_type->i_mutex_key#1 313962 [<ffffffff8027aa80>] generic_file_aio_write+0x4f/0xc2 &sb->s_type->i_mutex_key#1 0 [<ffffffff802a538c>] generic_file_llseek+0x36/0x98 second-run --------- &ei->i_data_sem-W: 0 0 0.00 0.00 0.00 2 61143 41.56 9299754.45 15811211.79 &ei->i_data_sem-R: 0 0 0.00 0.00 0.00 13272 82442 68.40 1632405.22 2877135.32 &sb->s_type->i_mutex_key#1: 441031 441163 10873.77 144350457.93 4988289572.34 441679 742079 163.05 15158665.56 59655118.60 -------------------------- &sb->s_type->i_mutex_key#1 441163 [<ffffffff802a538c>] generic_file_llseek+0x36/0x98 &sb->s_type->i_mutex_key#1 0 [<ffffffff8027aa80>] generic_file_aio_write+0x4f/0xc2 The test program is at http://www.radian.org/~kvaneesh/ext4/truncate_mutex/ The file system is modified to create highly fragmented file via frag.c - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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