[PATCH v12 7/9] kdump: add threshold for the required memory

[Chen Zhou <chenzhou10@huawei.com>]

For crashkernel=X, if required size X is too large and leads to very
little free low memory after low allocation, the system may not work
normally.
So add a threshold and go for high allocation directly if the required
size is too large. The value of threshold is set as the half of the
low memory.

Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
---
 kernel/crash_core.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 3f735cb37ace..d11d597a470d 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -378,6 +378,15 @@ int __init reserve_crashkernel_low(void)
 }
 
 #if defined(CONFIG_X86) || defined(CONFIG_ARM64)
+
+/*
+ * Add a threshold for required memory size of crashkernel. If required memory
+ * size is greater than threshold, just go for high allocation directly. The
+ * value of threshold is set as half of the total low memory.
+ */
+#define REQUIRED_MEMORY_THRESHOLD	(memblock_mem_size(CRASH_ADDR_LOW_MAX >> \
+			PAGE_SHIFT) >> 1)
+
 #ifdef CONFIG_KEXEC_CORE
 /*
  * reserve_crashkernel() - reserves memory for crash kernel
@@ -422,7 +431,7 @@ void __init reserve_crashkernel(void)
 		 * So try low memory first and fall back to high memory
 		 * unless "crashkernel=size[KMG],high" is specified.
 		 */
-		if (!high)
+		if (!high && crash_size <= REQUIRED_MEMORY_THRESHOLD)
 			crash_base = memblock_find_in_range(CRASH_ALIGN,
 						CRASH_ADDR_LOW_MAX,
 						crash_size, CRASH_ALIGN);
-- 
2.20.1