From 93a94f503b058a1452cc8b1eef389cbec5975863 Mon Sep 17 00:00:00 2001
From: Dan Smith <dansmith@redhat.com>
Date: Fri, 14 Dec 2018 06:39:59 -0800
Subject: [PATCH] Enable direct-io on LVM loop devices
This enables direct-io on the loop devices that we create for LVM backing
stores. The goal here is to reduce the buffer cache overhead involved with
loop mounting a very large file on a filesystem, as well as potentially
providing a little more block-device-like behavior for things that expect
them. We are hoping this will address some of the very long LVM calls that
cinder does, which randomly take a very long time, causing timeouts.
The loop direct-io support was added in kernel 4.4.0, which was xenial,
but the losetup binary does not have the required flag. Thus, this patch
checks the "losetup -h" output for the flag before deciding to enable it.
Change-Id: Idc69cf3598d6ed6646c0145733c90ad0b1b60883
---
lib/lvm | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/lib/lvm b/lib/lvm
index f0471816bf..d9e78a016f 100644
--- a/lib/lvm
+++ b/lib/lvm
@@ -99,8 +99,15 @@ function _create_lvm_volume_group {
if ! sudo vgs $vg; then
# Only create if the file doesn't already exists
[[ -f $backing_file ]] || truncate -s $size $backing_file
+
+ local directio=""
+ # Check to see if we can do direct-io
+ if losetup -h | grep -q direct-io; then
+ directio="--direct-io=on"
+ fi
+
local vg_dev
- vg_dev=`sudo losetup -f --show $backing_file`
+ vg_dev=$(sudo losetup -f --show $directio $backing_file)
# Only create volume group if it doesn't already exist
if ! sudo vgs $vg; then