nilfs2: improve execution time of NILFS_IOCTL_GET_CPINFO ioctl
The older a filesystem gets, the slower lscp command becomes. This is because nilfs_cpfile_do_get_cpinfo() function meets more hole blocks as the start offset of valid checkpoint numbers gets bigger. This reduces the overhead by skipping hole blocks efficiently with nilfs_mdt_find_block() helper. A measurement result of this patch is as follows: Before: $ time lscp CNO DATE TIME MODE FLG BLKCNT ICNT 5769303 2015-02-22 19:31:33 cp - 108 1 5769304 2015-02-22 19:38:54 cp - 108 1 real 0m0.182s user 0m0.003s sys 0m0.180s After: $ time lscp CNO DATE TIME MODE FLG BLKCNT ICNT 5769303 2015-02-22 19:31:33 cp - 108 1 5769304 2015-02-22 19:38:54 cp - 108 1 real 0m0.003s user 0m0.001s sys 0m0.002s Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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