[Linux-cluster] Behavior of "statfs_fast" settune

[Wendy Cheng]

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 ?

-- Wendy
> 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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