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Re: [Linux-cluster] Behavior of "statfs_fast" settune

Wendy Cheng wrote:
Mathieu Avila wrote:
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.
In theory, this shouldn't happen. Are you on RHEL 4 or RHEL 5 ? And what is the FS size that causes this problem ?

I just did a quick try. It doesn't happen to me. By reading your note, were you *repeatedly* issuing "gfs_tool settune .." then followed by "df" ? Remember the "settune" is expected to be run *once* right after the particular GFS filesystem is mounted. You certainly *can* run it multiple times. It won't hurt anything. However, each time the "settune" is invoked, the code has to perform a regular "df" (i.e. that's the way it initializes itself). I suspect this is the cause of your issue. Let me know either way.

-- Wendy

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