[Lustre-devel] Queries regarding LDLM_ENQUEUE

[bzzz.tomas at gmail.com <bzzz.tomas@gmail.com>]

On 10/20/10 9:29 PM, Nicolas Williams wrote:
> MDSes are typically CPU bound, so that's likely the issue.  The problem
> though is that the MDS does need to track open file state for SOM and
> for dealing with unlinks.  The semantics of open-by-handle might be such
> that unlinks of files opened by handle can cause the file to disappear
> and syscalls on FDs opened by handle could then return EBADF or EIO or
> some new error code.  But open-by-handle semantics don't allow for that,
> then the MDS needs to track open file state, and it's hard to see how to
> avoid RPCs to the MDS to establish that state (the original client could
> tell the MDS about all the clients that will open-by-handle, but this
> seems unlikely to perform so much better than N smaller RPCs as to
> justify it, and the open-by-handle API suddenly gets much more complex).

I guess for this purpose they may just disable SOM and do few steps away
from POSIX. probably inter-client data consistency isn't that important
any more ;) then get rid of MDS and namespace completely using some sort
of FID.

thanks, z