[PATCH v2] Documentation: add 'crashkernel=auto' entry into kernel-parameters.txt

[PATCH v2] Documentation: add 'crashkernel=auto' entry into kernel-parameters.txt

[Yaowei Bai]

There is no 'crashkernel=auto' entry in kernel-parameters.txt, borrow it
from kexec-kdump-howto.txt file in the kexec-tools-2.0.0 package.

Signed-off-by: Yaowei Bai <bywxiaobai@163.com>
---
 Documentation/kernel-parameters.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 1d6f045..9e5913e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -797,6 +797,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			It will be ignored when crashkernel=X,high is not used
 			or memory reserved is below 4G.
 
+	crashkernel=auto
+			This specification allows the kernel to decide how much
+			memory to reserve for the purposes of kdump. It will make
+			this determination based on the amount of memory you have
+			in your system, and scale the allocation accordingly.
+			Note that if you have less than 4Gb of memory in your system,
+			this specification will opt to not allocate any memory for
+			the purposes of kdump.
+
 	cs89x0_dma=	[HW,NET]
 			Format: <dma>
 
-- 
1.9.1

Re: [PATCH v2] Documentation: add 'crashkernel=auto' entry into kernel-parameters.txt

[Jonathan Corbet]

On Mon, 24 Aug 2015 23:04:29 +0800
Yaowei Bai <bywxiaobai@163.com> wrote:

> There is no 'crashkernel=auto' entry in kernel-parameters.txt, borrow it
> from kexec-kdump-howto.txt file in the kexec-tools-2.0.0 package.

OK, so I did some digging here.  As far as I can tell, there is no
crashkernel=auto entry because the auto-reserve patch has never been
merged into the mainline kernel.  RHEL kernels appear to have it, but
mainline doesn't.

Thus, merging this patch would make the documentation incorrect,
something I'd rather not do.  I appreciate efforts to improve the
kernel's documentation, but it is important to be sure that your proposed
changes make the docs closer to reality, rather than further away.

Thanks,

jon

Re: [PATCH v2] Documentation: add 'crashkernel=auto' entry into kernel-parameters.txt

[Yaowei Bai]

On Mon, Aug 24, 2015 at 11:26:23AM -0600, Jonathan Corbet wrote:
> On Mon, 24 Aug 2015 23:04:29 +0800
> Yaowei Bai <bywxiaobai@163.com> wrote:
> 
> > There is no 'crashkernel=auto' entry in kernel-parameters.txt, borrow it
> > from kexec-kdump-howto.txt file in the kexec-tools-2.0.0 package.
> 
> OK, so I did some digging here.  As far as I can tell, there is no
> crashkernel=auto entry because the auto-reserve patch has never been
> merged into the mainline kernel.  RHEL kernels appear to have it, but
> mainline doesn't.

Yes, it's indeed in the RHEL/CentOS kernels. This's my mistake.

> 
> Thus, merging this patch would make the documentation incorrect,
> something I'd rather not do.  I appreciate efforts to improve the
> kernel's documentation, but it is important to be sure that your proposed
> changes make the docs closer to reality, rather than further away.

Very appreciate your wonderful work.

> 
> Thanks,
> 
> jon