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Maximize the reserved size in osbuild case #92

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0021378
gen-kdump-sysconfig.sh: Fix shfmt check
Nov 21, 2025
37d35f6
kdump-lib: Extend _crashkernel_add() with a param
Sep 12, 2025
b78a909
kdump-lib_spec: Extend test for _crashkernel_add()
Sep 29, 2025
015e0f9
kdump-lib: Skip adding reserved memory for small-memory machine
Sep 22, 2025
1ef61a6
kdumpctl: Move _is_osbuild() to kdump-lib.sh
Sep 4, 2025
532ad21
crashkernel: Maximize the reserved size in osbuild case
Jun 23, 2025
7602d66
kdumpctl: Check the recommend value when starting service
Jun 24, 2025
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2 changes: 1 addition & 1 deletion gen-kdump-sysconfig.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@ fi
#
# Generate the config file
#
cat <<EOF
cat << EOF
# Kernel Version string for the -kdump kernel, such as 2.6.13-1544.FC5kdump
# If no version is specified, then the init script will try to find a
# kdump kernel with the same version number as the running kernel.
Expand Down
55 changes: 47 additions & 8 deletions kdump-lib.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ FADUMP_REGISTER_SYS_NODE="/sys/kernel/fadump/registered"
FADUMP_APPEND_ARGS_SYS_NODE="/sys/kernel/fadump/bootargs_append"
# shellcheck disable=SC2034
FENCE_KDUMP_CONFIG_FILE="/etc/sysconfig/fence_kdump"
maximize_crashkernel=false

is_fadump_capable()
{
Expand All @@ -35,7 +36,26 @@ is_aws_aarch64()

is_sme_or_sev_active()
{
journalctl -q --dmesg --grep "^Memory Encryption Features active: AMD (SME|SEV)$" > /dev/null 2>&1
$maximize_crashkernel || journalctl -q --dmesg --grep "^Memory Encryption Features active: AMD (SME|SEV)$" > /dev/null 2>&1
}

# read the value of an environ variable from given environ file path
#
# The environment variable entries in /proc/[pid]/environ are separated
# by null bytes instead of by spaces.
#
# $1: environment variable
# $2: environ file path
read_proc_environ_var()
{
local _var=$1 _environ_path=$2
sed -n -E "s/.*(^|\x00)${_var}=([^\x00]*).*/\2/p" < "$_environ_path"
}

_OSBUILD_ENVIRON_PATH='/proc/1/environ'
_is_osbuild()
{
[[ $(read_proc_environ_var container "$_OSBUILD_ENVIRON_PATH") == bwrap-osbuild ]]
}

has_command()
Expand Down Expand Up @@ -831,12 +851,19 @@ get_recommend_size()

has_mlx5()
{
[[ -d /sys/bus/pci/drivers/mlx5_core ]]
$maximize_crashkernel || [[ -d /sys/bus/pci/drivers/mlx5_core ]]
}

has_aarch64_smmu()
{
ls /sys/devices/platform/arm-smmu-* 1> /dev/null 2>&1
$maximize_crashkernel || ls /sys/devices/platform/arm-smmu-* 1> /dev/null 2>&1
}

is_aarch64_64k_kernel()
{
local _kernel="$1"
# the naming convention of 64k variant suffixes with +64k, e.g. "vmlinuz-5.14.0-312.el9.aarch64+64k"
$maximize_crashkernel || echo "$_kernel" | grep -q 64k
}

is_memsize()
Expand Down Expand Up @@ -946,13 +973,16 @@ _crashkernel_parse()

# $1 crashkernel command line parameter
# $2 size to be added
# $3 optionally skip the first n items in command line
_crashkernel_add()
{
local ck delta ret
local ck delta skip ret
local range size offset
local count=0

ck="$1"
delta="$2"
skip="${3:-0}" # Default to 0 if third parameter not provided
ret=""

while IFS=';' read -r size range offset; do
Expand All @@ -967,8 +997,12 @@ _crashkernel_add()
ret+="$range:"
fi

size=$(memsize_add "$size" "$delta") || return 1
if ((count >= skip)); then
size=$(memsize_add "$size" "$delta") || return 1
fi

ret+="$size,"
((count++))
done < <(_crashkernel_parse "$ck")

echo "${ret%,}"
Expand All @@ -982,7 +1016,11 @@ kdump_get_arch_recommend_crashkernel()
{
local _arch _ck_cmdline _dump_mode
local _delta=0
local _skip=0

# osbuild deploys rpm on isolated environment. kdump-utils has no opportunity
# to deduce the exact memory cost on the real target.
_is_osbuild && maximize_crashkernel=true
if [[ -z $1 ]]; then
if is_fadump_capable; then
_dump_mode=fadump
Expand All @@ -1008,9 +1046,10 @@ kdump_get_arch_recommend_crashkernel()
else
_running_kernel=$2
fi
# skip adding additional memory for small-memory machine
_skip=1

# the naming convention of 64k variant suffixes with +64k, e.g. "vmlinuz-5.14.0-312.el9.aarch64+64k"
if echo "$_running_kernel" | grep -q 64k; then
if is_aarch64_64k_kernel "$_running_kernel"; then
# Without smmu, the diff of MemFree between 4K and 64K measured on a high end aarch64 machine is 82M.
# Picking up 100M to cover this diff. And finally, we have "2G-4G:356M;4G-64G:420M;64G-:676M"
((_delta += 100))
Expand All @@ -1031,7 +1070,7 @@ kdump_get_arch_recommend_crashkernel()
fi
fi

echo -n "$(_crashkernel_add "$_ck_cmdline" "${_delta}M")"
echo -n "$(_crashkernel_add "$_ck_cmdline" "${_delta}M" "$_skip")"
}

# return recommended size based on current system RAM size
Expand Down
67 changes: 48 additions & 19 deletions kdumpctl
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Expand Up @@ -1210,6 +1210,53 @@ prepare_luks()
done
}

get_crashkernel_bounce_buffer_size()
{
local lines first_line start_hex end_hex start_dec end_dec size_bytes

mapfile -t lines < <(grep "Crash kernel" /proc/iomem)

if [ ${#lines[@]} -le 1 ]; then
echo 0
return
fi

first_line=${lines[0]}
# Extract start and end addresses
start_hex=$(echo "$first_line" | awk '{split($1, a, "-"); print a[1]}')
end_hex=$(echo "$first_line" | awk '{split($1, a, "-"); print a[2]}')
Comment on lines +1226 to +1227
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@gemini-code-assist gemini-code-assist bot Oct 15, 2025

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medium

These two lines invoke awk twice on the same input ($first_line) to extract the start and end addresses. This is inefficient. You can achieve the same result with a single awk command and read, which is cleaner and more performant.

Suggested change
start_hex=$(echo "$first_line" | awk '{split($1, a, "-"); print a[1]}')
end_hex=$(echo "$first_line" | awk '{split($1, a, "-"); print a[2]}')
read -r start_hex end_hex < <(echo "$first_line" | awk '{split($1, a, "-"); print a[1], a[2]}')

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@coiby coiby Oct 30, 2025

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Hi @pfliu this suggestion from Gemini seems to make sense, what do you think?

# Convert hex to decimal
start_dec=$((0x$start_hex))
end_dec=$((0x$end_hex))
# Calculate size in bytes
size_bytes=$((end_dec - start_dec + 1))
echo "$size_bytes"
}

suggest_crashkernel_reset()
{
local _crashkernel _recommend_value _actual_value _bounce_buff_size

_crashkernel=$(sed -n 's/.*crashkernel=\([^ ]*\).*/\1/p' /proc/cmdline)
[[ $(kdump_get_conf_val auto_reset_crashkernel) == no ]] && return
# At present, the crashkernel value for fadump is not dynamic
is_fadump_capable && return

_recommend_value=$(kdump_get_arch_recommend_size)
# The crashkernel formula does not account for DMA-bounce buffers,
# unlike kexec_crash_size which does. Systems using DMA-bounce buffers
# should factor this into the calculation.
_bounce_buff_size=$(get_crashkernel_bounce_buffer_size)
_recommend_value=$(memsize_add "$_recommend_value" "$_bounce_buff_size")
_recommend_value=$(to_bytes "$_recommend_value")
_actual_value=$(cat /sys/kernel/kexec_crash_size)

if [ "$_recommend_value" -lt "$_actual_value" ]; then
dwarn "The reserved crashkernel is abundant. Using 'kdumpctl reset-crashkernel' to reset kernel cmdline. It will take effect in the next boot"
dwarn "To release the abundant memory immediately, you can run: 'kdumpctl stop; echo $_recommend_value >/sys/kernel/kexec_crash_size; kdumpctl start'"
fi
}

start()
{
check_dump_feasibility || return
Expand Down Expand Up @@ -1243,6 +1290,7 @@ start()
start_dump || return

dinfo "Starting kdump: [OK]"
suggest_crashkernel_reset
return 0
}

Expand Down Expand Up @@ -1970,25 +2018,6 @@ reset_crashkernel_after_update()
done
}

# read the value of an environ variable from given environ file path
#
# The environment variable entries in /proc/[pid]/environ are separated
# by null bytes instead of by spaces.
#
# $1: environment variable
# $2: environ file path
read_proc_environ_var()
{
local _var=$1 _environ_path=$2
sed -n -E "s/.*(^|\x00)${_var}=([^\x00]*).*/\2/p" < "$_environ_path"
}

_OSBUILD_ENVIRON_PATH='/proc/1/environ'
_is_osbuild()
{
[[ $(read_proc_environ_var container "$_OSBUILD_ENVIRON_PATH") == bwrap-osbuild ]]
}

reset_crashkernel_for_installed_kernel()
{
local _installed_kernel _grub_entry_index _kernel _old_ck _old_fadump
Expand Down
21 changes: 20 additions & 1 deletion spec/kdump-lib_spec.sh
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Expand Up @@ -51,7 +51,7 @@ Describe 'kdump-lib'
End

Describe "_crashkernel_add()"
Context "For valid input values"
Context "For valid input values with two arguments (skip defaults to 0)"
Parameters
"2G-4G:256M,4G-64G:320M,64G-:576M" "100M" "2G-4G:356M,4G-64G:420M,64G-:676M"
"2G-4G:256M" "100" "2G-4G:268435556" # avoids any rounding when size % 1024 != 0
Expand All @@ -74,6 +74,25 @@ Describe 'kdump-lib'
The output should equal "$3"
End
End

Context "For valid input values with three arguments (explicit skip)"
Parameters
"2G-4G:256M,4G-64G:320M,64G-:576M" "100M" "1" "2G-4G:256M,4G-64G:420M,64G-:676M"
"2G-4G:256M,4G-64G:320M,64G-:576M" "100M" "2" "2G-4G:256M,4G-64G:320M,64G-:676M"
"2G-4G:256M,4G-64G:320M,64G-:576M" "100M" "3" "2G-4G:256M,4G-64G:320M,64G-:576M"
"2G-4G:256M,4G-64G:320M,64G-:576M@4G" "100M" "1" "2G-4G:256M,4G-64G:420M,64G-:676M@4G"
"2G-4G:1G,4G-64G:2G,64G-:3G@4G" "100M" "1" "2G-4G:1G,4G-64G:2148M,64G-:3172M@4G"
"2G-4G:10000K,4G-64G:20000K" "100M" "1" "2G-4G:10000K,4G-64G:122400K"
"1M@1G" "1K" "1" "1M@1G"
"128G-1T:4G,10T-100T:1T" "1G" "1" "128G-1T:4G,10T-100T:1025G"
"1K,low" "1" "1" "1K,low"
End
It "should add delta to values after ':' starting after skip count"
When call _crashkernel_add "$1" "$2" "$3"
The output should equal "$4"
End
End

Context "For invalid input values"
Parameters
"2G-4G:256M.4G-64G:320M" "100M"
Expand Down
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