[PATCHv3] powerpc/crashkernel: take "mem=" option into account

[Pingfan Liu <kernelfans@gmail.com>]

'mem=" option is an easy way to put high pressure on memory during some
test. Hence after applying the memory limit, instead of total mem, the
actual usable memory should be considered when reserving mem for
crashkernel. Otherwise the boot up may experience OOM issue.

E.g. it would reserve 4G prior to the change and 512M afterward, if passing
crashkernel="2G-4G:384M,4G-16G:512M,16G-64G:1G,64G-128G:2G,128G-:4G", and
mem=5G on a 256G machine.

This issue is powerpc specific because it puts higher priority on fadump
and kdump reservation than on "mem=". Referring the following code:
	if (fadump_reserve_mem() == 0)
		reserve_crashkernel();
	...
	/* Ensure that total memory size is page-aligned. */
	limit = ALIGN(memory_limit ?: memblock_phys_mem_size(), PAGE_SIZE);
	memblock_enforce_memory_limit(limit);

While on other arches, the effect of "mem=" takes a higher priority and pass
through memblock_phys_mem_size() before calling reserve_crashkernel().

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: kexec@lists.infradead.org
---
v2 -> v3: improve commit log
 arch/powerpc/kernel/machine_kexec.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/machine_kexec.c b/arch/powerpc/kernel/machine_kexec.c
index c4ed328..eec96dc 100644
--- a/arch/powerpc/kernel/machine_kexec.c
+++ b/arch/powerpc/kernel/machine_kexec.c
@@ -114,11 +114,12 @@ void machine_kexec(struct kimage *image)
 
 void __init reserve_crashkernel(void)
 {
-	unsigned long long crash_size, crash_base;
+	unsigned long long crash_size, crash_base, total_mem_sz;
 	int ret;
 
+	total_mem_sz = memory_limit ? memory_limit : memblock_phys_mem_size();
 	/* use common parsing */
-	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
+	ret = parse_crashkernel(boot_command_line, total_mem_sz,
 			&crash_size, &crash_base);
 	if (ret == 0 && crash_size > 0) {
 		crashk_res.start = crash_base;
@@ -185,7 +186,7 @@ void __init reserve_crashkernel(void)
 			"for crashkernel (System RAM: %ldMB)\n",
 			(unsigned long)(crash_size >> 20),
 			(unsigned long)(crashk_res.start >> 20),
-			(unsigned long)(memblock_phys_mem_size() >> 20));
+			(unsigned long)(total_mem_sz >> 20));
 
 	if (!memblock_is_region_memory(crashk_res.start, crash_size) ||
 	    memblock_reserve(crashk_res.start, crash_size)) {
-- 
2.7.5