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From f03ee48fab36a9fe55082f15111771b698081598 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Renaud=20M=C3=A9trich?= <rmetrich@redhat.com>
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Date: Wed, 5 May 2021 15:46:08 +0200
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Subject: [PATCH] fix(dracut-functions): implement a cache for get_maj_min
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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On systems with a large number of devices, usually multipath devices,
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dracut can spend a lot of time stat'ing the devices to collect the
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major/minor numbers, leading to huge slowness rebuilding the initramfs
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when stat'ing devices is slow (seen with oracleasm file systems in
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particular).
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This commit implements a basic cache stored in a file under
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DRACUT_TMPDIR storing the major:minor corresponding to the specified
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device.
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Reproducer: create N loopback devices used as a LVM extension to volume
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group hosting the root file system
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# LVMVG="rhel"
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# NDEVICES=200
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# mkdir devices; for i in $(seq 1 $NDEVICES); do
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truncate -s 10m devices/$i; losetup loop$i devices/$i
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done
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# vgextend $LVMVG $(/bin/ls -1 /dev/loop[0-9]*)
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With standard code (tested with RHEL8.3 dracut):
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# dracut -f --debug /tmp/initramfs.img $(uname -r) >/tmp/debug 2>&1
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# grep -c "stat -L -c" /tmp/debug
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2440
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With this code:
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# dracut -f --debug /tmp/initramfs.img $(uname -r) >/tmp/debug_optim 2>&1
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# grep -c "stat -L -c" /tmp/debug_optim
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205
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Signed-off-by: Renaud Métrich <rmetrich@redhat.com>
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(cherry picked from commit c3bb9d18dceed7db6d16f9c2a7f682c5934099d7)
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Cherry-picked from: c3bb9d18dceed7db6d16f9c2a7f682c5934099d7
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Resolves: #1957622
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---
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dracut-functions.sh | 10 +++++++---
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dracut.sh | 4 ++++
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2 files changed, 11 insertions(+), 3 deletions(-)
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diff --git a/dracut-functions.sh b/dracut-functions.sh
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index 1431dd18..a221967c 100755
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--- a/dracut-functions.sh
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+++ b/dracut-functions.sh
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@@ -199,12 +199,16 @@ get_fs_env() {
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# $ get_maj_min /dev/sda2
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# 8:2
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get_maj_min() {
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- local _maj _min _majmin
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+ local _majmin
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+ out="$(grep -m1 -oP "^$1 \K\S+$" "${get_maj_min_cache_file:?}")"
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+ if [ -z "$out" ]; then
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_majmin="$(stat -L -c '%t:%T' "$1" 2>/dev/null)"
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- printf "%s" "$((0x${_majmin%:*})):$((0x${_majmin#*:}))"
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+ out="$(printf "%s" "$((0x${_majmin%:*})):$((0x${_majmin#*:}))")"
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+ echo "$1 $out" >> "${get_maj_min_cache_file:?}"
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+ fi
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+ echo -n "$out"
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}
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-
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# get_devpath_block <device>
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# get the DEVPATH in /sys of a block device
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get_devpath_block() {
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diff --git a/dracut.sh b/dracut.sh
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index 4340e646..f8e68ccb 100755
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--- a/dracut.sh
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+++ b/dracut.sh
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@@ -901,6 +901,10 @@ readonly DRACUT_TMPDIR="$(mktemp -p "$TMPDIR/" -d -t dracut.XXXXXX)"
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exit 1
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}
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+# Cache file used to optimize get_maj_min()
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+declare -x -r get_maj_min_cache_file="${DRACUT_TMPDIR}/majmin_cache"
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+: > "$get_maj_min_cache_file"
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+
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# clean up after ourselves no matter how we die.
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trap '
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ret=$?;
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