On 02/23/2010 10:10 PM, Wu Fengguang wrote:
Collect readahead stats when CONFIG_READAHEAD_STATS=y. This is enabled by default because the added overheads are trivial: two readahead_stats() calls per readahead. Example output: (taken from a fresh booted NFS-ROOT box with rsize=16k) $ cat /debug/readahead/stats pattern readahead eof_hit cache_hit io sync_io mmap_io size async_size io_size initial 524 216 26 498 498 18 7 4 4 subsequent 181 80 1 130 13 60 25 25 24 context 94 28 3 85 64 8 7 2 5 thrash 0 0 0 0 0 0 0 0 0 around 162 121 33 162 162 162 60 0 21 fadvise 0 0 0 0 0 0 0 0 0 random 137 0 0 137 137 0 1 0 1 all 1098 445 63 1012 874 0 17 6 9 The two most important columns are - io number of readahead IO - io_size average readahead IO size CC: Ingo Molnar<mingo@xxxxxxx> CC: Jens Axboe<jens.axboe@xxxxxxxxxx> CC: Peter Zijlstra<a.p.zijlstra@xxxxxxxxx> Signed-off-by: Wu Fengguang<fengguang.wu@xxxxxxxxx>
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