fuse/readdirp: Remove need_lookup from fuse_readdirp_cbk

background: Various xlators used to populate their ctx, on
an explicit lookup. That means without a lookup, the translator will have
either null or stale data to function. E.g. dht would depend on lookup to
create linkto files on the correct node/hashed subvol, afr would rely on
this lookup to heal pending data/metadata etc.

So to complete above actions a lookup used to be issued on files,
even their inode was populated on a readdirp_cbk. This was done
by setting the need_lookup flag on all the files those were read
on readdirp fop.

We tried a small test on "ACL client". For listing 50k files on root
itself, it took around 50seconds with readdirp enabled while
the same operation took 5-6 seconds with readdirp disabled. Both the
times md-cache was enabled.

We observed that on the 1st test case (readdirp enabled), post readdirp
a getxattr is done. The number of getxattr depends on the number of acl
xattrs (I saw requests on these two: system.posix_acl_default,
system.posix_acl_access). Since need_lookup flag is set, during fuse_resolve
a nameless lookup is executed on the inode(getxattr being inode operation,
hence the nameless lookup). Since md-cache does not serve nameless lookup,
a network hop is needed for each file, costing the time.

With readdirp disabled, the getxattrs are served from md-cache itself(note:
we are discussing the 2nd attempt of ls -l use case).

_Current affairs around need of lookup for a file to populate it's ctx_:

For the xlators on client stack we discussed quite extensively about the need
for a lookup fop post readdirp in all three cluster translators - afr, EC and
dht. EC and dht don't really need a nameless lookup post readdirp. For afr too,
the need for lookup was negated with patch (http://review.gluster.org/6010 - AFRV2),
where  afr added a function called afr_inode_refresh() which does a lookup and
populates its inode context in case a FOP came to AFR without a lookup being issued
prior to it.

We ran a thread on gluster-devel asking for feedback on the need of explicit lookup
post readdirp. For responses refer [1]. Refer [2] for discussions happened on gerrit.
After gathering inputs from [1] and [2], it looks like there is no xlator in
current state that requires an explicit lookup post readdirp to function properly.

* A separate similar patch will be sent for gfapi/nfs/nfs-ganesha.

Note: Only file's inode is built with readdirp.

[1] http://lists.gluster.org/pipermail/gluster-devel/2017-August/053505.html
[2] https://review.gluster.org/#/c/17985/

Change-Id: Ie1d68ce7bea5e1f8a1fab9a62217f478322554f5
BUG: 1492996
Signed-off-by: Susant Palai <spalai@redhat.com>

0 files changed, 0 insertions, 0 deletions