[Lustre-discuss] How to you generated discarded readahead pages?
Mark Seger
Mark.Seger at hp.com
Sat Mar 22 06:10:10 PDT 2008
I'm running a little script that does 3 consecutive small reads of 4K
each and then sleeps for a second and as you can see from the following
collectl output readahead is happening. How do I know? Because the
network traffic is so high:
# <----------Network----------><-------------Lustre
Client-------------->
#Time netKBi pkt-in netKBo pkt-out Reads KBRead Writes KBWrite
Hits Misses
09:31:54 1084 740 29 394 3 12 0 0
0 3
09:31:55 1084 740 29 394 3 12 0 0
0 3
09:31:56 1084 740 29 394 3 12 0 0
0 3
09:31:57 1084 741 29 394 2 8 0 0
0 2
I'm getting my data from
/proc/fs/lustre/llite/spfs1-00000100768c2800/read_ahead_stats and when I
look at the disards, they're not changing. What I would like to know is
why. as I'd think all that extra data would be discarded from the
cache. Is it because some other process needs to put pressure on it? I
have 4GB memory and just wrote a 5GB file which should certain force out
anything already there but the counter never changed.
I do see "readpage not consecutive" changing,
-mark
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