quick-read, md-cache: selectively cache xattr data to conserve memory

The md-cache translator can cache items for a long period of time and
thus is sensitive to memory usage associated with the items it
references. This implements two changes to help conserve memory:

- quick-read - Migrate the file content data to a local dict and
	delete from the xdata dict that passes through the stack.
- md-cache - Create a local dict to selectively store the xattr
	data md-cache is interested in. This includes a slight
	optimization to not allocate an empty dict in the case
	where we have not received any xattr's of interest.

I've tested both changes independently and together by running a
readdirp test against several compiled source trees (~340k files).
The base test results in a 7.7GB RSS on the client. The quick-read
modification cuts RSS down to 4.1GB, which is still large due
to md-cache unintelligently caching a large number of empty
dictionaries. The combined modification cuts RSS down to 462MB
on the same workload.

NOTE: Theoretically the md-cache change should supercede the
quick-read change, but practically I save an extra 150MB or so with
both. I already had the change and consider it an improvement that
quick-read clean up after itself.

BUG: 812876
Change-Id: Id59734d12dd6476b0e32480939e633448adb6884
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-on: http://review.gluster.com/3268
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavendra G <raghavendra@gluster.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>

1 files changed, 20 insertions, 1 deletions

diff --git a/xlators/performance/quick-read/src/quick-read.c b/xlators/performance/quick-read/src/quick-read.c
index beddfd878a8..000dcb45400 100644
--- a/xlators/performance/quick-read/src/quick-read.c
+++ b/xlators/performance/quick-read/src/quick-read.c
@@ -429,13 +429,32 @@ qr_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                         }
                 }
 
+		/*
+		 * Create our own internal dict and migrate the file content
+		 * over to it so it isn't floating around in other translator
+		 * caches.
+		 */
                 if (qr_inode->xattr) {
                         dict_unref (qr_inode->xattr);
                         qr_inode->xattr = NULL;
                         table->cache_used -= qr_inode->stbuf.ia_size;
                 }
 
-                qr_inode->xattr = dict_ref (xdata);
+		qr_inode->xattr = dict_new();
+		if (!qr_inode->xattr) {
+			op_ret = -1;
+			op_errno = ENOMEM;
+			goto unlock;
+		}
+
+		if (dict_set(qr_inode->xattr, GF_CONTENT_KEY, content) < 0) {
+			op_ret = -1;
+			op_errno = ENOMEM;
+			goto unlock;
+		}
+
+		dict_del(xdata, GF_CONTENT_KEY);
+
                 qr_inode->stbuf = *buf;
                 table->cache_used += buf->ia_size;