Always set vm.zone_reclaim_mode = 3 in kdump kernel

By default kernel have vm.zone_reclaim_mode = 0 and large page
allocation might fail as kernel is very conservative on memory
reclaiming. If the page allocation failure is not handled carefully
it could lead to more serious problems.

This issue can be reproduced by change with following steps:

- Fill up page cache use:
  # dd if=/dev/urandom of=/test bs=1M count=1300

- Now the memory is filled with write cache:
  # free -m
                total        used        free      shared  buff/cache   available
  Mem:           1790         184         132           2        1473        1348
  Swap:          2119           7        2112

- Insert a module which simply calls "kmalloc(SZ_1M, GFP_KERNEL)" for
  512 times: (Notice: vmalloc don't have such problem)
  # insmod debug_module.ko

- Got following allocation failure:
  insmod: page allocation failure: order:8, mode:0x40cc0(GFP_KERNEL|__GFP_COMP), nodemask=(null),cpuset=/,mems_allowed=0

- Clean up and repeat again with vm.zone_reclaim_mode = 3, OOM is not
  observed.

In kdump kernel there is usually only one online CPU and limited memory,
so we set vm.zone_reclaim_mode = 3 to let kernel reclaim memory more
aggresively to avoid such issue.

Signed-off-by: Kairui Song <kasong@redhat.com>
Acked-by: Pingfan Liu <piliu@redhat.com>

dracut-module-setup.sh

@@ -537,16 +537,18 @@ kdump_install_conf() {
     rm -f ${initdir}/tmp/$$-kdump.conf
 }
 
-# Default sysctl parameters should suffice for kdump kernel.
-# Remove custom configurations sysctl.conf & sysctl.d/*
-remove_sysctl_conf() {
-
+# Remove user custom configurations sysctl.conf & sysctl.d/*
+# and apply some optimization for kdump
+overwrite_sysctl_conf() {
     # As custom configurations like vm.min_free_kbytes can lead
     # to OOM issues in kdump kernel, avoid them
     rm -f "${initdir}/etc/sysctl.conf"
     rm -rf "${initdir}/etc/sysctl.d"
     rm -rf "${initdir}/run/sysctl.d"
     rm -rf "${initdir}/usr/lib/sysctl.d"
+
+    mkdir -p "${initdir}/etc/sysctl.d"
+    echo "vm.zone_reclaim_mode = 3" > "${initdir}/etc/sysctl.d/99-zone-reclaim.conf"
 }
 
 kdump_iscsi_get_rec_val() {
@@ -812,7 +814,7 @@ kdump_install_random_seed() {
 
 install() {
     kdump_install_conf
-    remove_sysctl_conf
+    overwrite_sysctl_conf
 
     if is_ssh_dump_target; then
         kdump_install_random_seed