[Ocfs2-devel] [SUGGESSTION 1/1] OCFS2: automatic dlm hash table size

[Sunil Mushran <sunil.mushran@oracle.com>]

Wengang Wang wrote:
> just increasing it works. I'm concerning memory waste for few inodes
> usage case. I don't know how large it is going to be in the future..
> even now, I just don't hope a memory waste though it's small though
> memory is cheap now... :)

So, we did discuss dynamic resizing of the lockres hash over a
year ago. At that time our hash was very small. 1 page in 1.2,
and 4 pages in 1.4-beta/mainline. At that time, we decided to
bump up the default in 1.4 to 64 pages.

Resizing requires a feedback loop. As in... lookup is taking too
much time. I am working on adding instrumentation that provides this
info. (The number of lockres' is too crude a stat.)

Once we have that, I would prefer we make the lock per chain instead
of a global. That will allow us to get more bang for the buck. Will
allow us to reduce the hashtable from 64 pages.

In the end, I am not yet sold on dynamic resizing. One data point is
that inode/dcache hashes are not dynamically resized.