write-behind: Allow trickling-writes to be configurable, fix usage of page_size and window_size

Summary:
- It adds a configurable option for "trickling-writes".
- Makes `__wb_preprocess_winds()` use `wb_inode->window_conf` rather
  than `page_size`, so that the window-size option is actually
  respected.
- This is a port of D3576122 & D3738605 to 3.8.

Test Plan:
- Prove test which looks @ brick-level FOPs and ensures
that they fall in the right write-size bucket.

Reviewed By: rwareing

Signature: t1:3576122:1468892648:6923a6a19b18888577ce5173b5c9cb9531f941e7

Change-Id: I379a9f2f0c4768c9052b7e9dd71c5f0469cb2d68
Signed-off-by: Shreyas Siravara <sshreyas@fb.com>
Reviewed-on: http://review.gluster.org/16079
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Kevin Vigor <kvigor@fb.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>

0 files changed, 0 insertions, 0 deletions