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sysconfig: disable kfence in kdump kernel

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Resolves: RHEL-103425
Upstream: kdump-utils
Conflict: None

Signed-off-by: Baoquan He <bhe@redhat.com>
This commit is contained in:
Baoquan He 2025-08-06 11:54:32 +08:00
parent 647ca6bdfa
commit bfa3841787
2 changed files with 48 additions and 0 deletions
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47
0005-sysconfig-disable-kfence-in-kdump-kernel.patch Normal file
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@ -0,0 +1,47 @@
From ddb0bab1f7e1e43a802993aadad03f85a3c045a9 Mon Sep 17 00:00:00 2001
From: Baoquan He <bhe@redhat.com>
Date: Wed, 25 Jun 2025 23:30:24 +0800
Subject: [PATCH] sysconfig: disable kfence in kdump kernel
Content-type: text/plain
In the current fedora and RHEL, below config items related to kfence
feature are set by default:
===
CONFIG_HAVE_ARCH_KFENCE=y
CONFIG_KFENCE=y
CONFIG_KFENCE_SAMPLE_INTERVAL=100
CONFIG_KFENCE_NUM_OBJECTS=255
CONFIG_KFENCE_STRESS_TEST_FAULTS=0
CONFIG_KFENCE_KUNIT_TEST=m
===
With them set, on x86_64, it will cost 2M extra memory used for kfence when
page size if 4K; while on arm64 with 64K page size, it will cost 32M extra
memory. This doesn't take memory cost of initializing and running kfence
itself into account, here only saying the kfence objects and guarded
pages. However, it doesn't make any sense to have kfence in a kdump
kernel. Hence, disable kfence in kdump kernel to save crashkernel
memory.
Signed-off-by: Baoquan He <bhe@redhat.com>
---
gen-kdump-sysconfig.sh | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/gen-kdump-sysconfig.sh b/gen-kdump-sysconfig.sh
index 8ed63ba6eb9d..ca2e7610bc59 100755
--- a/gen-kdump-sysconfig.sh
+++ b/gen-kdump-sysconfig.sh
@@ -29,7 +29,7 @@ KDUMP_COMMANDLINE_REMOVE="hugepages hugepagesz slub_debug quiet log_buf_len swio
# This variable lets us append arguments to the current kdump commandline
# after processed by KDUMP_COMMANDLINE_REMOVE
-KDUMP_COMMANDLINE_APPEND="irqpoll maxcpus=1 reset_devices novmcoredd cma=0 hugetlb_cma=0"
+KDUMP_COMMANDLINE_APPEND="irqpoll maxcpus=1 reset_devices novmcoredd cma=0 hugetlb_cma=0 kfence.sample_interval=0"
# This variable lets us append arguments to fadump (powerpc) capture kernel,
# further to the parameters passed via the bootloader.
--
2.41.0

1
kdump-utils.spec
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@ -12,6 +12,7 @@ Patch01: 0001-kdumpctl-check-and-generate-etc-vconsole.conf.patch
Patch02: 0002-mkdumprd-replace-lz4hc-with-lzma-for-better-compress.patch
Patch03: 0003-Fix-the-way-to-tell-if-there-is-a-need-to-set-up-net.patch
Patch04: 0004-Support-dumping-to-NVMe-TCP-configured-using-NVMe-Bo.patch
Patch05: 0005-sysconfig-disable-kfence-in-kdump-kernel.patch
%ifarch ppc64 ppc64le
Requires(post): servicelog