Problem: Before executing a fop in POSIX xlator it builds an internal
path based on GFID.To validate the path it call's (l)stat
system call and while .glusterfs is heavily loaded kernel takes
time to lookup inode and due to that performance drops
Solution: In this patch we followed two ways to improve the performance.
1) Keep open fd specific to first level directory(gfid[0])
in .glusterfs, it would force to kernel keep the inodes
from all those files in cache. In case of memory pressure
kernel won't uncache first level inodes. We need to open
256 fd's per brick to access the entry faster.
2) Use at based call's to access relative path to reduce
path based lookup time.
Note: To verify the patch we have executed kernel untar 100 times on 6
different clients after enabling metadata group-cache and some
other option.We were getting more than 20 percent improvement in
kenel untar after applying the patch.
Credits: Xavi Hernandez <xhernandez@redhat.com>
Change-Id: I1643e6b01ed669b2bb148d02f4e6a8e08da45343
updates: #891
Signed-off-by: Mohit Agrawal <moagrawal@redhat.com>