[PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation

[PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation

[dyoung]

[-- Attachment #1: kdump-crashkernel-roundup-total-mem.patch --]
[-- Type: text/plain, Size: 2197 bytes --]

The total memory size we get in kernel is usually slightly less than 2G with a
2G memory module machine. The main reason is bios/firmware reserve some area
it will not export all memory as usable to Linux.

2G memory X86 kvm guest test result of the total_mem value:
UEFI boot with ovmf: 0x7ef10000
Legacy boot kvm guest: 0x7ff7cc00

An option is to use dmi/smbios to get physical memory size, but it's not
reliable as well. According to Prarit hardware vendors sometimes screw this up.
Thus we choose to round up total size to 128M to workaround this problem.
This is a best effort workaround, will improve it when we have better way
in the future. 

Signed-off-by: Dave Young <dyoung@redhat.com>
---
 kernel/crash_core.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

--- linux.orig/kernel/crash_core.c
+++ linux/kernel/crash_core.c
@@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem(
 {
 	char *cur = cmdline, *tmp;
 	bool infinite_end = false;
+	unsigned long long total_mem = system_ram;
+
+	/*
+	 * Firmware usually reserves some memory regions for it's own use.
+	 * so we get less than actual system memory size.
+	 * We workaround this by round up the total size to 128M which is
+	 * enough for most test cases.
+	 */
+	total_mem = roundup(total_mem, 0x8000000);
 
 	/* for each entry of the comma-separated list */
 	do {
@@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem(
 			return -EINVAL;
 		}
 		cur = tmp;
-		if (size >= system_ram) {
+		if (size >= total_mem) {
 			pr_warn("crashkernel: invalid size\n");
 			return -EINVAL;
 		}
 
 		/* match ? */
-		if (system_ram >= start && system_ram < end) {
+		if (total_mem >= start && total_mem < end) {
 			*crash_size = size;
 			if (end == ULLONG_MAX)
 				infinite_end = true;
@@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem(
 				pr_warn("Memory reservation scale order expected after '^'\n");
 				return -EINVAL;
 			}
-			size = (system_ram - *crash_size) >> shift;
+			size = (total_mem - *crash_size) >> shift;
 			size = *crash_size + roundup(size, 1ULL << 20);
-			if (size < system_ram)
+			if (size < total_mem)
 				*crash_size = size;
 			cur = tmp;
 		} else

[PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation

[dyoung]

[-- Attachment #1: kdump-crashkernel-roundup-total-mem.patch --]
[-- Type: text/plain, Size: 2343 bytes --]

The total memory size we get in kernel is usually slightly less than 2G with a
2G memory module machine. The main reason is bios/firmware reserve some area
it will not export all memory as usable to Linux.

2G memory X86 kvm guest test result of the total_mem value:
UEFI boot with ovmf: 0x7ef10000
Legacy boot kvm guest: 0x7ff7cc00

An option is to use dmi/smbios to get physical memory size, but it's not
reliable as well. According to Prarit hardware vendors sometimes screw this up.
Thus we choose to round up total size to 128M to workaround this problem.
This is a best effort workaround, will improve it when we have better way
in the future. 

Signed-off-by: Dave Young <dyoung@redhat.com>
---
 kernel/crash_core.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

--- linux.orig/kernel/crash_core.c
+++ linux/kernel/crash_core.c
@@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem(
 {
 	char *cur = cmdline, *tmp;
 	bool infinite_end = false;
+	unsigned long long total_mem = system_ram;
+
+	/*
+	 * Firmware usually reserves some memory regions for it's own use.
+	 * so we get less than actual system memory size.
+	 * We workaround this by round up the total size to 128M which is
+	 * enough for most test cases.
+	 */
+	total_mem = roundup(total_mem, 0x8000000);
 
 	/* for each entry of the comma-separated list */
 	do {
@@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem(
 			return -EINVAL;
 		}
 		cur = tmp;
-		if (size >= system_ram) {
+		if (size >= total_mem) {
 			pr_warn("crashkernel: invalid size\n");
 			return -EINVAL;
 		}
 
 		/* match ? */
-		if (system_ram >= start && system_ram < end) {
+		if (total_mem >= start && total_mem < end) {
 			*crash_size = size;
 			if (end == ULLONG_MAX)
 				infinite_end = true;
@@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem(
 				pr_warn("Memory reservation scale order expected after '^'\n");
 				return -EINVAL;
 			}
-			size = (system_ram - *crash_size) >> shift;
+			size = (total_mem - *crash_size) >> shift;
 			size = *crash_size + roundup(size, 1ULL << 20);
-			if (size < system_ram)
+			if (size < total_mem)
 				*crash_size = size;
 			cur = tmp;
 		} else



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Re: [PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation

[Baoquan He]

Hi Dave,

On 10/24/17 at 01:31pm, Dave Young wrote:
> The total memory size we get in kernel is usually slightly less than 2G with a
> 2G memory module machine. The main reason is bios/firmware reserve some area
> it will not export all memory as usable to Linux.
> 
> 2G memory X86 kvm guest test result of the total_mem value:
> UEFI boot with ovmf: 0x7ef10000
> Legacy boot kvm guest: 0x7ff7cc00
> 
> An option is to use dmi/smbios to get physical memory size, but it's not
> reliable as well. According to Prarit hardware vendors sometimes screw this up.
> Thus we choose to round up total size to 128M to workaround this problem.
> This is a best effort workaround, will improve it when we have better way
> in the future. 

Thanks for this posting. While I don't get the point of this patch. So
firmware take piece of memory, then why we need to count it into the
total memory which we want to calculate a crashkernel memory based on.

Not counting that, is there anyting incorrect?

Thanks
Baoquan

> 
> Signed-off-by: Dave Young <dyoung@redhat.com>
> ---
>  kernel/crash_core.c |   17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> --- linux.orig/kernel/crash_core.c
> +++ linux/kernel/crash_core.c
> @@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem(
>  {
>  	char *cur = cmdline, *tmp;
>  	bool infinite_end = false;
> +	unsigned long long total_mem = system_ram;
> +
> +	/*
> +	 * Firmware usually reserves some memory regions for it's own use.
> +	 * so we get less than actual system memory size.
> +	 * We workaround this by round up the total size to 128M which is
> +	 * enough for most test cases.
> +	 */
> +	total_mem = roundup(total_mem, 0x8000000);
>  
>  	/* for each entry of the comma-separated list */
>  	do {
> @@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem(
>  			return -EINVAL;
>  		}
>  		cur = tmp;
> -		if (size >= system_ram) {
> +		if (size >= total_mem) {
>  			pr_warn("crashkernel: invalid size\n");
>  			return -EINVAL;
>  		}
>  
>  		/* match ? */
> -		if (system_ram >= start && system_ram < end) {
> +		if (total_mem >= start && total_mem < end) {
>  			*crash_size = size;
>  			if (end == ULLONG_MAX)
>  				infinite_end = true;
> @@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem(
>  				pr_warn("Memory reservation scale order expected after '^'\n");
>  				return -EINVAL;
>  			}
> -			size = (system_ram - *crash_size) >> shift;
> +			size = (total_mem - *crash_size) >> shift;
>  			size = *crash_size + roundup(size, 1ULL << 20);
> -			if (size < system_ram)
> +			if (size < total_mem)
>  				*crash_size = size;
>  			cur = tmp;
>  		} else
> 
> 

Re: [PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation

[Baoquan He]

Hi Dave,

On 10/24/17 at 01:31pm, Dave Young wrote:
> The total memory size we get in kernel is usually slightly less than 2G with a
> 2G memory module machine. The main reason is bios/firmware reserve some area
> it will not export all memory as usable to Linux.
> 
> 2G memory X86 kvm guest test result of the total_mem value:
> UEFI boot with ovmf: 0x7ef10000
> Legacy boot kvm guest: 0x7ff7cc00
> 
> An option is to use dmi/smbios to get physical memory size, but it's not
> reliable as well. According to Prarit hardware vendors sometimes screw this up.
> Thus we choose to round up total size to 128M to workaround this problem.
> This is a best effort workaround, will improve it when we have better way
> in the future. 

Thanks for this posting. While I don't get the point of this patch. So
firmware take piece of memory, then why we need to count it into the
total memory which we want to calculate a crashkernel memory based on.

Not counting that, is there anyting incorrect?

Thanks
Baoquan

> 
> Signed-off-by: Dave Young <dyoung@redhat.com>
> ---
>  kernel/crash_core.c |   17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> --- linux.orig/kernel/crash_core.c
> +++ linux/kernel/crash_core.c
> @@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem(
>  {
>  	char *cur = cmdline, *tmp;
>  	bool infinite_end = false;
> +	unsigned long long total_mem = system_ram;
> +
> +	/*
> +	 * Firmware usually reserves some memory regions for it's own use.
> +	 * so we get less than actual system memory size.
> +	 * We workaround this by round up the total size to 128M which is
> +	 * enough for most test cases.
> +	 */
> +	total_mem = roundup(total_mem, 0x8000000);
>  
>  	/* for each entry of the comma-separated list */
>  	do {
> @@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem(
>  			return -EINVAL;
>  		}
>  		cur = tmp;
> -		if (size >= system_ram) {
> +		if (size >= total_mem) {
>  			pr_warn("crashkernel: invalid size\n");
>  			return -EINVAL;
>  		}
>  
>  		/* match ? */
> -		if (system_ram >= start && system_ram < end) {
> +		if (total_mem >= start && total_mem < end) {
>  			*crash_size = size;
>  			if (end == ULLONG_MAX)
>  				infinite_end = true;
> @@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem(
>  				pr_warn("Memory reservation scale order expected after '^'\n");
>  				return -EINVAL;
>  			}
> -			size = (system_ram - *crash_size) >> shift;
> +			size = (total_mem - *crash_size) >> shift;
>  			size = *crash_size + roundup(size, 1ULL << 20);
> -			if (size < system_ram)
> +			if (size < total_mem)
>  				*crash_size = size;
>  			cur = tmp;
>  		} else
> 
> 

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Re: [PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation

[Dave Young]

Hi Baoquan,

On 10/24/17 at 01:57pm, Baoquan He wrote:
> Hi Dave,
> 
> On 10/24/17 at 01:31pm, Dave Young wrote:
> > The total memory size we get in kernel is usually slightly less than 2G with a
> > 2G memory module machine. The main reason is bios/firmware reserve some area
> > it will not export all memory as usable to Linux.
> > 
> > 2G memory X86 kvm guest test result of the total_mem value:
> > UEFI boot with ovmf: 0x7ef10000
> > Legacy boot kvm guest: 0x7ff7cc00
> > 
> > An option is to use dmi/smbios to get physical memory size, but it's not
> > reliable as well. According to Prarit hardware vendors sometimes screw this up.
> > Thus we choose to round up total size to 128M to workaround this problem.
> > This is a best effort workaround, will improve it when we have better way
> > in the future. 
> 
> Thanks for this posting. While I don't get the point of this patch. So
> firmware take piece of memory, then why we need to count it into the
> total memory which we want to calculate a crashkernel memory based on.
> 
> Not counting that, is there anyting incorrect?

Yes, considering crashkernel=1G-2G:128M,  if we have a 1G memory
machine, we get total size 1023M from firmware then it will not fall
into 1G-2G thus no memory reserved.  User will never know that, it is
hard to let user to know the exact total value we get in kernel..

> 
> Thanks
> Baoquan
> 
> > 
> > Signed-off-by: Dave Young <dyoung@redhat.com>
> > ---
> >  kernel/crash_core.c |   17 +++++++++++++----
> >  1 file changed, 13 insertions(+), 4 deletions(-)
> > 
> > --- linux.orig/kernel/crash_core.c
> > +++ linux/kernel/crash_core.c
> > @@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem(
> >  {
> >  	char *cur = cmdline, *tmp;
> >  	bool infinite_end = false;
> > +	unsigned long long total_mem = system_ram;
> > +
> > +	/*
> > +	 * Firmware usually reserves some memory regions for it's own use.
> > +	 * so we get less than actual system memory size.
> > +	 * We workaround this by round up the total size to 128M which is
> > +	 * enough for most test cases.
> > +	 */
> > +	total_mem = roundup(total_mem, 0x8000000);
> >  
> >  	/* for each entry of the comma-separated list */
> >  	do {
> > @@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem(
> >  			return -EINVAL;
> >  		}
> >  		cur = tmp;
> > -		if (size >= system_ram) {
> > +		if (size >= total_mem) {
> >  			pr_warn("crashkernel: invalid size\n");
> >  			return -EINVAL;
> >  		}
> >  
> >  		/* match ? */
> > -		if (system_ram >= start && system_ram < end) {
> > +		if (total_mem >= start && total_mem < end) {
> >  			*crash_size = size;
> >  			if (end == ULLONG_MAX)
> >  				infinite_end = true;
> > @@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem(
> >  				pr_warn("Memory reservation scale order expected after '^'\n");
> >  				return -EINVAL;
> >  			}
> > -			size = (system_ram - *crash_size) >> shift;
> > +			size = (total_mem - *crash_size) >> shift;
> >  			size = *crash_size + roundup(size, 1ULL << 20);
> > -			if (size < system_ram)
> > +			if (size < total_mem)
> >  				*crash_size = size;
> >  			cur = tmp;
> >  		} else
> > 
> > 

Thanks
Dave

Re: [PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation

[Dave Young]

Hi Baoquan,

On 10/24/17 at 01:57pm, Baoquan He wrote:
> Hi Dave,
> 
> On 10/24/17 at 01:31pm, Dave Young wrote:
> > The total memory size we get in kernel is usually slightly less than 2G with a
> > 2G memory module machine. The main reason is bios/firmware reserve some area
> > it will not export all memory as usable to Linux.
> > 
> > 2G memory X86 kvm guest test result of the total_mem value:
> > UEFI boot with ovmf: 0x7ef10000
> > Legacy boot kvm guest: 0x7ff7cc00
> > 
> > An option is to use dmi/smbios to get physical memory size, but it's not
> > reliable as well. According to Prarit hardware vendors sometimes screw this up.
> > Thus we choose to round up total size to 128M to workaround this problem.
> > This is a best effort workaround, will improve it when we have better way
> > in the future. 
> 
> Thanks for this posting. While I don't get the point of this patch. So
> firmware take piece of memory, then why we need to count it into the
> total memory which we want to calculate a crashkernel memory based on.
> 
> Not counting that, is there anyting incorrect?

Yes, considering crashkernel=1G-2G:128M,  if we have a 1G memory
machine, we get total size 1023M from firmware then it will not fall
into 1G-2G thus no memory reserved.  User will never know that, it is
hard to let user to know the exact total value we get in kernel..

> 
> Thanks
> Baoquan
> 
> > 
> > Signed-off-by: Dave Young <dyoung@redhat.com>
> > ---
> >  kernel/crash_core.c |   17 +++++++++++++----
> >  1 file changed, 13 insertions(+), 4 deletions(-)
> > 
> > --- linux.orig/kernel/crash_core.c
> > +++ linux/kernel/crash_core.c
> > @@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem(
> >  {
> >  	char *cur = cmdline, *tmp;
> >  	bool infinite_end = false;
> > +	unsigned long long total_mem = system_ram;
> > +
> > +	/*
> > +	 * Firmware usually reserves some memory regions for it's own use.
> > +	 * so we get less than actual system memory size.
> > +	 * We workaround this by round up the total size to 128M which is
> > +	 * enough for most test cases.
> > +	 */
> > +	total_mem = roundup(total_mem, 0x8000000);
> >  
> >  	/* for each entry of the comma-separated list */
> >  	do {
> > @@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem(
> >  			return -EINVAL;
> >  		}
> >  		cur = tmp;
> > -		if (size >= system_ram) {
> > +		if (size >= total_mem) {
> >  			pr_warn("crashkernel: invalid size\n");
> >  			return -EINVAL;
> >  		}
> >  
> >  		/* match ? */
> > -		if (system_ram >= start && system_ram < end) {
> > +		if (total_mem >= start && total_mem < end) {
> >  			*crash_size = size;
> >  			if (end == ULLONG_MAX)
> >  				infinite_end = true;
> > @@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem(
> >  				pr_warn("Memory reservation scale order expected after '^'\n");
> >  				return -EINVAL;
> >  			}
> > -			size = (system_ram - *crash_size) >> shift;
> > +			size = (total_mem - *crash_size) >> shift;
> >  			size = *crash_size + roundup(size, 1ULL << 20);
> > -			if (size < system_ram)
> > +			if (size < total_mem)
> >  				*crash_size = size;
> >  			cur = tmp;
> >  		} else
> > 
> > 

Thanks
Dave

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Re: [PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation

[Baoquan He]

On 10/24/17 at 02:09pm, Dave Young wrote:
> Hi Baoquan,
> 
> On 10/24/17 at 01:57pm, Baoquan He wrote:
> > Hi Dave,
> > 
> > On 10/24/17 at 01:31pm, Dave Young wrote:
> > > The total memory size we get in kernel is usually slightly less than 2G with a
> > > 2G memory module machine. The main reason is bios/firmware reserve some area
> > > it will not export all memory as usable to Linux.
> > > 
> > > 2G memory X86 kvm guest test result of the total_mem value:
> > > UEFI boot with ovmf: 0x7ef10000
> > > Legacy boot kvm guest: 0x7ff7cc00
> > > 
> > > An option is to use dmi/smbios to get physical memory size, but it's not
> > > reliable as well. According to Prarit hardware vendors sometimes screw this up.
> > > Thus we choose to round up total size to 128M to workaround this problem.
> > > This is a best effort workaround, will improve it when we have better way
> > > in the future. 
> > 
> > Thanks for this posting. While I don't get the point of this patch. So
> > firmware take piece of memory, then why we need to count it into the
> > total memory which we want to calculate a crashkernel memory based on.
> > 
> > Not counting that, is there anyting incorrect?
> 
> Yes, considering crashkernel=1G-2G:128M,  if we have a 1G memory
> machine, we get total size 1023M from firmware then it will not fall
> into 1G-2G thus no memory reserved.  User will never know that, it is
> hard to let user to know the exact total value we get in kernel..

OK, got it. Thanks.

Then I have no objection to this. See what other reviewers will say.

Thanks
Baoquan


> > 
> > > 
> > > Signed-off-by: Dave Young <dyoung@redhat.com>
> > > ---
> > >  kernel/crash_core.c |   17 +++++++++++++----
> > >  1 file changed, 13 insertions(+), 4 deletions(-)
> > > 
> > > --- linux.orig/kernel/crash_core.c
> > > +++ linux/kernel/crash_core.c
> > > @@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem(
> > >  {
> > >  	char *cur = cmdline, *tmp;
> > >  	bool infinite_end = false;
> > > +	unsigned long long total_mem = system_ram;
> > > +
> > > +	/*
> > > +	 * Firmware usually reserves some memory regions for it's own use.
> > > +	 * so we get less than actual system memory size.
> > > +	 * We workaround this by round up the total size to 128M which is
> > > +	 * enough for most test cases.
> > > +	 */
> > > +	total_mem = roundup(total_mem, 0x8000000);
> > >  
> > >  	/* for each entry of the comma-separated list */
> > >  	do {
> > > @@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem(
> > >  			return -EINVAL;
> > >  		}
> > >  		cur = tmp;
> > > -		if (size >= system_ram) {
> > > +		if (size >= total_mem) {
> > >  			pr_warn("crashkernel: invalid size\n");
> > >  			return -EINVAL;
> > >  		}
> > >  
> > >  		/* match ? */
> > > -		if (system_ram >= start && system_ram < end) {
> > > +		if (total_mem >= start && total_mem < end) {
> > >  			*crash_size = size;
> > >  			if (end == ULLONG_MAX)
> > >  				infinite_end = true;
> > > @@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem(
> > >  				pr_warn("Memory reservation scale order expected after '^'\n");
> > >  				return -EINVAL;
> > >  			}
> > > -			size = (system_ram - *crash_size) >> shift;
> > > +			size = (total_mem - *crash_size) >> shift;
> > >  			size = *crash_size + roundup(size, 1ULL << 20);
> > > -			if (size < system_ram)
> > > +			if (size < total_mem)
> > >  				*crash_size = size;
> > >  			cur = tmp;
> > >  		} else
> > > 
> > > 
> 
> Thanks
> Dave

Re: [PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation

[Baoquan He]

On 10/24/17 at 02:09pm, Dave Young wrote:
> Hi Baoquan,
> 
> On 10/24/17 at 01:57pm, Baoquan He wrote:
> > Hi Dave,
> > 
> > On 10/24/17 at 01:31pm, Dave Young wrote:
> > > The total memory size we get in kernel is usually slightly less than 2G with a
> > > 2G memory module machine. The main reason is bios/firmware reserve some area
> > > it will not export all memory as usable to Linux.
> > > 
> > > 2G memory X86 kvm guest test result of the total_mem value:
> > > UEFI boot with ovmf: 0x7ef10000
> > > Legacy boot kvm guest: 0x7ff7cc00
> > > 
> > > An option is to use dmi/smbios to get physical memory size, but it's not
> > > reliable as well. According to Prarit hardware vendors sometimes screw this up.
> > > Thus we choose to round up total size to 128M to workaround this problem.
> > > This is a best effort workaround, will improve it when we have better way
> > > in the future. 
> > 
> > Thanks for this posting. While I don't get the point of this patch. So
> > firmware take piece of memory, then why we need to count it into the
> > total memory which we want to calculate a crashkernel memory based on.
> > 
> > Not counting that, is there anyting incorrect?
> 
> Yes, considering crashkernel=1G-2G:128M,  if we have a 1G memory
> machine, we get total size 1023M from firmware then it will not fall
> into 1G-2G thus no memory reserved.  User will never know that, it is
> hard to let user to know the exact total value we get in kernel..

OK, got it. Thanks.

Then I have no objection to this. See what other reviewers will say.

Thanks
Baoquan


> > 
> > > 
> > > Signed-off-by: Dave Young <dyoung@redhat.com>
> > > ---
> > >  kernel/crash_core.c |   17 +++++++++++++----
> > >  1 file changed, 13 insertions(+), 4 deletions(-)
> > > 
> > > --- linux.orig/kernel/crash_core.c
> > > +++ linux/kernel/crash_core.c
> > > @@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem(
> > >  {
> > >  	char *cur = cmdline, *tmp;
> > >  	bool infinite_end = false;
> > > +	unsigned long long total_mem = system_ram;
> > > +
> > > +	/*
> > > +	 * Firmware usually reserves some memory regions for it's own use.
> > > +	 * so we get less than actual system memory size.
> > > +	 * We workaround this by round up the total size to 128M which is
> > > +	 * enough for most test cases.
> > > +	 */
> > > +	total_mem = roundup(total_mem, 0x8000000);
> > >  
> > >  	/* for each entry of the comma-separated list */
> > >  	do {
> > > @@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem(
> > >  			return -EINVAL;
> > >  		}
> > >  		cur = tmp;
> > > -		if (size >= system_ram) {
> > > +		if (size >= total_mem) {
> > >  			pr_warn("crashkernel: invalid size\n");
> > >  			return -EINVAL;
> > >  		}
> > >  
> > >  		/* match ? */
> > > -		if (system_ram >= start && system_ram < end) {
> > > +		if (total_mem >= start && total_mem < end) {
> > >  			*crash_size = size;
> > >  			if (end == ULLONG_MAX)
> > >  				infinite_end = true;
> > > @@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem(
> > >  				pr_warn("Memory reservation scale order expected after '^'\n");
> > >  				return -EINVAL;
> > >  			}
> > > -			size = (system_ram - *crash_size) >> shift;
> > > +			size = (total_mem - *crash_size) >> shift;
> > >  			size = *crash_size + roundup(size, 1ULL << 20);
> > > -			if (size < system_ram)
> > > +			if (size < total_mem)
> > >  				*crash_size = size;
> > >  			cur = tmp;
> > >  		} else
> > > 
> > > 
> 
> Thanks
> Dave

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[PATCH 3/3 update] kdump: round up the total memory size to 128M for crashkernel reservation

[Dave Young]

The total memory size we get in kernel is usually slightly less than 2G with a
2G memory module machine. The main reason is bios/firmware reserve some area
it will not export all memory as usable to Linux.

2G memory X86 kvm guest test result of the total_mem value:
UEFI boot with ovmf: 0x7ef10000
Legacy boot kvm guest: 0x7ff7cc00
This is also a problem on arm64 UEFI booted system according to my test.

Thus for example crashkernel=1G-2G:128M,  if we have a 1G memory
machine, we get total size 1023M from firmware then it will not fall
into 1G-2G thus no memory reserved.

An option is to use dmi/smbios to get physical memory size, but it's not
reliable as well. According to Prarit hardware vendors sometimes screw this up.
Thus round up total size to 128M to workaround this problem.

Signed-off-by: Dave Young <dyoung@redhat.com>
---
Changes from previous version of 3/3:
1. improve changelog: add examples why this is a problem (comment from
   Baoquan He)
2. change to use SZ_128M (comment from Bhupesh Sharma)

 kernel/crash_core.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- linux-x86.orig/kernel/crash_core.c
+++ linux-x86/kernel/crash_core.c
@@ -9,6 +9,7 @@
 #include <linux/crash_core.h>
 #include <linux/utsname.h>
 #include <linux/vmalloc.h>
+#include <linux/sizes.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -42,6 +43,15 @@ static int __init parse_crashkernel_mem(
 {
 	char *cur = cmdline, *tmp;
 	bool infinite_end = false;
+	unsigned long long total_mem = system_ram;
+
+	/*
+	 * Firmware usually reserves some memory regions for it's own use.
+	 * so we get less than actual system memory size.
+	 * We workaround this by round up the total size to 128M which is
+	 * enough for most test cases.
+	 */
+	total_mem = roundup(total_mem, SZ_128M);
 
 	/* for each entry of the comma-separated list */
 	do {
@@ -86,13 +96,13 @@ static int __init parse_crashkernel_mem(
 			return -EINVAL;
 		}
 		cur = tmp;
-		if (size >= system_ram) {
+		if (size >= total_mem) {
 			pr_warn("crashkernel: invalid size\n");
 			return -EINVAL;
 		}
 
 		/* match ? */
-		if (system_ram >= start && system_ram < end) {
+		if (total_mem >= start && total_mem < end) {
 			*crash_size = size;
 			if (end == ULLONG_MAX)
 				infinite_end = true;
@@ -126,9 +136,9 @@ static int __init parse_crashkernel_mem(
 				pr_warn("Memory reservation scale order expected after '^'\n");
 				return -EINVAL;
 			}
-			size = (system_ram - *crash_size) >> shift;
+			size = (total_mem - *crash_size) >> shift;
 			size = *crash_size + roundup(size, 1ULL << 20);
-			if (size < system_ram)
+			if (size < total_mem)
 				*crash_size = size;
 			cur = tmp;
 		} else

[PATCH 3/3 update] kdump: round up the total memory size to 128M for crashkernel reservation

[Dave Young]

The total memory size we get in kernel is usually slightly less than 2G with a
2G memory module machine. The main reason is bios/firmware reserve some area
it will not export all memory as usable to Linux.

2G memory X86 kvm guest test result of the total_mem value:
UEFI boot with ovmf: 0x7ef10000
Legacy boot kvm guest: 0x7ff7cc00
This is also a problem on arm64 UEFI booted system according to my test.

Thus for example crashkernel=1G-2G:128M,  if we have a 1G memory
machine, we get total size 1023M from firmware then it will not fall
into 1G-2G thus no memory reserved.

An option is to use dmi/smbios to get physical memory size, but it's not
reliable as well. According to Prarit hardware vendors sometimes screw this up.
Thus round up total size to 128M to workaround this problem.

Signed-off-by: Dave Young <dyoung@redhat.com>
---
Changes from previous version of 3/3:
1. improve changelog: add examples why this is a problem (comment from
   Baoquan He)
2. change to use SZ_128M (comment from Bhupesh Sharma)

 kernel/crash_core.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- linux-x86.orig/kernel/crash_core.c
+++ linux-x86/kernel/crash_core.c
@@ -9,6 +9,7 @@
 #include <linux/crash_core.h>
 #include <linux/utsname.h>
 #include <linux/vmalloc.h>
+#include <linux/sizes.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -42,6 +43,15 @@ static int __init parse_crashkernel_mem(
 {
 	char *cur = cmdline, *tmp;
 	bool infinite_end = false;
+	unsigned long long total_mem = system_ram;
+
+	/*
+	 * Firmware usually reserves some memory regions for it's own use.
+	 * so we get less than actual system memory size.
+	 * We workaround this by round up the total size to 128M which is
+	 * enough for most test cases.
+	 */
+	total_mem = roundup(total_mem, SZ_128M);
 
 	/* for each entry of the comma-separated list */
 	do {
@@ -86,13 +96,13 @@ static int __init parse_crashkernel_mem(
 			return -EINVAL;
 		}
 		cur = tmp;
-		if (size >= system_ram) {
+		if (size >= total_mem) {
 			pr_warn("crashkernel: invalid size\n");
 			return -EINVAL;
 		}
 
 		/* match ? */
-		if (system_ram >= start && system_ram < end) {
+		if (total_mem >= start && total_mem < end) {
 			*crash_size = size;
 			if (end == ULLONG_MAX)
 				infinite_end = true;
@@ -126,9 +136,9 @@ static int __init parse_crashkernel_mem(
 				pr_warn("Memory reservation scale order expected after '^'\n");
 				return -EINVAL;
 			}
-			size = (system_ram - *crash_size) >> shift;
+			size = (total_mem - *crash_size) >> shift;
 			size = *crash_size + roundup(size, 1ULL << 20);
-			if (size < system_ram)
+			if (size < total_mem)
 				*crash_size = size;
 			cur = tmp;
 		} else

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