linux-kernel - [PATCH 2/2] arm64/kdump: add code comments for crashkernel reservation cases

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Message-Id: <20230117034921.185150-3-bhe@redhat.com>
Date:   Tue, 17 Jan 2023 11:49:21 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        catalin.marinas@....com, will@...nel.org,
        thunder.leizhen@...wei.com, John.p.donnelly@...cle.com,
        wangkefeng.wang@...wei.com, Baoquan He <bhe@...hat.com>
Subject: [PATCH 2/2] arm64/kdump: add code comments for crashkernel reservation cases

This will help understand codes on crashkernel reservations on arm64.

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 arch/arm64/mm/init.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 26a05af2bfa8..f88ad17cb20d 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -177,6 +177,10 @@ static void __init reserve_crashkernel(void)
 	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
 					       search_base, crash_max);
 	if (!crash_base) {
+		/*
+		 * For crashkernel=size[KMG]@offset[KMG], print out failure
+		 * message if can't reserve the specified region.
+		 */
 		if (fixed_base) {
 			pr_warn("cannot reserve crashkernel region [0x%llx-0x%llx]\n",
 				search_base, crash_max);
@@ -188,6 +192,11 @@ static void __init reserve_crashkernel(void)
 		 * high memory, the minimum required low memory will be
 		 * reserved later.
 		 */
+		/*
+		 * For crashkernel=size[KMG], if the first attempt was for
+		 * low memory, fall back to high memory, the minimum required
+		 * low memory will be reserved later.
+		 */
 		if (!high && crash_max == CRASH_ADDR_LOW_MAX) {
 			crash_max = CRASH_ADDR_HIGH_MAX;
 			search_base = CRASH_ADDR_LOW_MAX;
@@ -195,6 +204,10 @@ static void __init reserve_crashkernel(void)
 			goto retry;
 		}
 
+		/*
+		 * For crashkernel=size[KMG],high, if the first attempt was for
+		 * high memory, fall back to low memory.
+		 */
 		if (high && (crash_max == CRASH_ADDR_HIGH_MAX)) {
 			crash_max = CRASH_ADDR_LOW_MAX;
 			search_base = 0;
-- 
2.34.1