[Linux-cluster] Behavior of "statfs_fast" settune

[Mathieu Avila]

Hello GFS developers,

I am in the process of evaluating the performance gain of
the "statfs_fast" patch.
Once the FS is mounted, I perform "gfs_tool settune  ...." and then i
measure the time to perform "df" on a partially filled FS. The time is
almost the same, "df" returns almost instantly, with a value really
near the truth, and progressively reaching the true one.

But I have noticed that when the FS size increases, the time to
perform  "gfs_tool settune  ...." increases dramatically. In fact,
after a few measures, it appears that the time to perform "df" without
fuzzy statfs is the same as the time to activate fuzzy statfs. 

I've read the patch, and from what I understand, there is an inode used
to store the fuzzy value of statfs, read once and updated later in
background. So the behavior i experienced shouldn't happen. So, please,
what am I doing wrong ?

--
Mathieu


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