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

'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 <redacted>
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

Hello Pingfan,

Thanks for the patch..

On 19/02/20 7:48 PM, Pingfan Liu wrote:

memory_limit is adjusted after this with the below snippet:

        /* Crash kernel trumps memory limit */
        if (memory_limit && memory_limit <= crashk_res.end) {                           
                memory_limit = crashk_res.end + 1;
                printk("Adjusted memory limit for crashkernel, now 0x%llx\n",           
                       memory_limit);                                                   
        } 

So, either the above snippet must be dropped or the print below should use an updated total_mem_sz
based on adjusted memory_limit. I would prefer the latter..

-- 
- Hari

'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 <redacted>
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
---
v3 -> v4: fix total_mem_sz based on adjusted memory_limit

 arch/powerpc/kexec/core.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
index 078fe3d..56da5eb 100644
--- a/arch/powerpc/kexec/core.c
+++ b/arch/powerpc/kexec/core.c

@@ -115,11 +115,12 @@ 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;

@@ -178,6 +179,7 @@ void __init reserve_crashkernel(void)
 	/* Crash kernel trumps memory limit */
 	if (memory_limit && memory_limit <= crashk_res.end) {
 		memory_limit = crashk_res.end + 1;
+		total_mem_sz = memory_limit;
 		printk("Adjusted memory limit for crashkernel, now 0x%llx\n",
 		       memory_limit);
 	}

@@ -186,7 +188,7 @@ 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

On 01/04/20 7:30 PM, Pingfan Liu wrote:

'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().

quoted

Signed-off-by: Pingfan Liu <redacted>

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
---
v3 -> v4: fix total_mem_sz based on adjusted memory_limit

Thanks for the update.

Reviewed-by: Hari Bathini <hbathini@linux.ibm.com>

On Wed, 1 Apr 2020 22:00:44 +0800, Pingfan Liu wrote:

'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.

[...]

Applied to powerpc/next.

[1/1] powerpc/crashkernel: Take "mem=" option into account
      https://git.kernel.org/powerpc/c/be5470e0c285a68dc3afdea965032f5ddc8269d7

cheers