[Cluster-devel] [RFC]Drop unused plock resource when no other plock request comes

[Jiaju Zhang <jjzhang.linux@gmail.com>]

Hello,

Currently, it seems that dlm_controld won't drop an unused plock resource
(which has exceed the timeout) when there is no another plock request for
other resource comes. I found this issue when I run the pingpong test case
http://junkcode.samba.org/ftp/unpacked/junkcode/ping_pong.c
In the pingpong, it just uses fcntl(F_SETLKW) to lock/unlock a file
repeatedly to see the lock performance. Now, my test case is:
Step 1: start pingpong on node A, then stop it.
Step 2: after a while(more than 10 seconds), start pingpong on node B.
I haven't run the pingpong concurrently on the two nodes, but the lock
performance in node A is much higher than in node B.
The user might be confused about why the performance on the two nodes seems
so different.

After some investigating, I found the reason is when running pingpong on
node A, r->owner == A, so all the plock requests operates locally. When
pingpong stops on node A, there is no other plock request comes from node A,
so the drop_resources won't be triggered even if it has exceed the timeout.
Then, pingpong on node B and it found r->owner == A so eventually it turned
into the state r->owner == 0. This is the distributed mode, so the
performance is decreasing.

It seems no chance to trigger the drop_resources to work if there is no
other plock requests (which are requesting for another lock resource) come
from node A.
But I still wonder if there is a way to improve this?

Thanks,
Jiaju
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