storage/posix: implement batched fsync in a single thread

Because of the extra fsync()s issued by AFR transaction, they
could potentially "clog" all the io-threads denying unrelated
operations from making progress.

This patch assigns a dedicated thread to issues fsyncs, as
an experimental feature to understand performance characteristics
with the approach.

As a basis, incoming individual fsync requests are grouped into
batches, falling in the same @batch-fsync-delay-usec window of
time. These windows can extend in practice, as processing of
the previous batch can take longer than @batch-fsync-delay-usec
while new requests are getting batched.

The feature support three modes (similar to the -S modes of fs_mark)

- syncfs: In this mode one syncfs() is issued per batch, instead
  of N fsync()s (one per file.)

- syncfs-single-fsync: In this mode one syncfs() is issued per
  batch (which, on Linux, guarantees the completion of write-out
  of dirty pages in the filesystem up to that point) and one single
  fsync() to synchronize or flush the controller/drive cache. This
  corresponds to -S 2 of fsmark.

- syncfs-reverse-fsync: In this mode, one syncfs() is issued per
  batch, and all the open files in that batch are fsync()'ed in
  the reverse order of the queue. This corresponds to -S 4 of
  fsmark.

- reverse-fsync: In this mode, no syncfs() is issued and all the
  files in the batch are fsync()'ed in the reverse order. This
  corresponds to -S 3 of fsmark.

Change-Id: Ia1e170a810c780c8d80e02cf910accc4170c4cd4
BUG: 927146
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/4746
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/xlators/cluster/afr/src/afr-transaction.c b/xlators/cluster/afr/src/afr-transaction.c
index d6d420910cf..def00e28834 100644
--- a/xlators/cluster/afr/src/afr-transaction.c
+++ b/xlators/cluster/afr/src/afr-transaction.c
@@ -1478,6 +1478,8 @@ afr_changelog_fsync (call_frame_t *frame, xlator_t *this)
         int i = 0;
         int call_count = 0;
         afr_private_t *priv = NULL;
+ 	dict_t *xdata = NULL;
+ 	GF_UNUSED int ret = -1;
 
         local = frame->local;
         priv = this->private;
@@ -1493,6 +1495,10 @@ afr_changelog_fsync (call_frame_t *frame, xlator_t *this)
 
         local->call_count = call_count;
 
+	xdata = dict_new();
+	if (xdata)
+		ret = dict_set_int32 (xdata, "batch-fsync", 1);
+
         for (i = 0; i < priv->child_count; i++) {
                 if (!local->transaction.pre_op[i])
                         continue;
@@ -1500,11 +1506,14 @@ afr_changelog_fsync (call_frame_t *frame, xlator_t *this)
                 STACK_WIND_COOKIE (frame, afr_changelog_fsync_cbk,
                                 (void *) (long) i, priv->children[i],
                                 priv->children[i]->fops->fsync, local->fd,
-                                1, NULL);
+                                1, xdata);
                 if (!--call_count)
                         break;
         }
 
+	if (xdata)
+		dict_unref (xdata);
+
         return 0;
 }