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  2. Commit 93a94f503b058a1452cc8b1eef389cbec5975863
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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

Dan Smith authored on 2018/12/14 23:39:59
Showing 1 changed files
lib/lvm
History View file @ 93a94f5
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@@ -99,8 +99,15 @@ function _create_lvm_volume_group {
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     if ! sudo vgs $vg; then
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         # Only create if the file doesn't already exists
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         [[ -f $backing_file ]] || truncate -s $size $backing_file
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+
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+        local directio=""
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+        # Check to see if we can do direct-io
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+        if losetup -h | grep -q direct-io; then
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+            directio="--direct-io=on"
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+        fi
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+
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         local vg_dev
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-        vg_dev=`sudo losetup -f --show $backing_file`
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+        vg_dev=$(sudo losetup -f --show $directio $backing_file)
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         # Only create volume group if it doesn't already exist
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         if ! sudo vgs $vg; then