(Also applicable over 2.6.38-rc3)
Had to explore two C code files to make sense of the 'crashkernel='
kernel parameter values. Improve the situation.
Signed-off-by: Ahmed S. Darwish <[email protected]>
---
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 89835a4..8f26b42 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
Format:
<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
- crashkernel=nn[KMG]@ss[KMG]
- [KNL] Reserve a chunk of physical memory to
- hold a kernel to switch to with kexec on panic.
+ crashkernel=size[KMG][@offset[KMG]]
+ [KNL] Using kexec, Linux can switch to a 'crash kernel'
+ upon panic. This parameter reserves the physical
+ memory region [offset, offset + size] for that kernel
+ image. If the '@offset' part was ignored, Linux finds
+ a suitable crash image start address automatically.
crashkernel=range1:size1[,range2:size2,...][@offset]
[KNL] Same as above, but depends on the memory
regards,
--
Darwish
http://darwish.07.googlepages.com
On Sun, Feb 06, 2011 at 05:41:08PM +0200, Ahmed S. Darwish wrote:
> (Also applicable over 2.6.38-rc3)
>
> Had to explore two C code files to make sense of the 'crashkernel='
> kernel parameter values. Improve the situation.
>
> Signed-off-by: Ahmed S. Darwish <[email protected]>
> ---
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 89835a4..8f26b42 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
> Format:
> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
>
> - crashkernel=nn[KMG]@ss[KMG]
> - [KNL] Reserve a chunk of physical memory to
> - hold a kernel to switch to with kexec on panic.
> + crashkernel=size[KMG][@offset[KMG]]
> + [KNL] Using kexec, Linux can switch to a 'crash kernel'
> + upon panic. This parameter reserves the physical
> + memory region [offset, offset + size] for that kernel
> + image. If the '@offset' part was ignored, Linux finds
> + a suitable crash image start address automatically.
I think this would be further improved as:
... If '@offset' is omitted then a suitable
offset is selected automatically.
>
> crashkernel=range1:size1[,range2:size2,...][@offset]
> [KNL] Same as above, but depends on the memory
>
> regards,
>
> --
> Darwish
> http://darwish.07.googlepages.com
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>
On 02/06/2011 03:57 PM, Simon Horman wrote:
> On Sun, Feb 06, 2011 at 05:41:08PM +0200, Ahmed S. Darwish wrote:
>> (Also applicable over 2.6.38-rc3)
>>
>> Had to explore two C code files to make sense of the 'crashkernel='
>> kernel parameter values. Improve the situation.
>>
>> Signed-off-by: Ahmed S. Darwish <[email protected]>
>> ---
>>
>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index 89835a4..8f26b42 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
>> Format:
>> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
>>
>> - crashkernel=nn[KMG]@ss[KMG]
>> - [KNL] Reserve a chunk of physical memory to
>> - hold a kernel to switch to with kexec on panic.
>> + crashkernel=size[KMG][@offset[KMG]]
>> + [KNL] Using kexec, Linux can switch to a 'crash kernel'
>> + upon panic. This parameter reserves the physical
>> + memory region [offset, offset + size] for that kernel
>> + image. If the '@offset' part was ignored, Linux finds
>> + a suitable crash image start address automatically.
>
> I think this would be further improved as:
>
> ... If '@offset' is omitted then a suitable
> offset is selected automatically.
Suitable offset as in parses a known image type (ELF, bzImage, etc) to
find the start address? Or just assumes the entry point and load
address are the same?
Is this the size for just the kernel image, or also for the physical
memory it uses so it won't overwrite the existing kernel's stuff on the
way up? (If a compressed kernel wants to decompress itself or extract
an initramfs for itself, what happens?)
Rob
Rob Landley <[email protected]> writes:
2> On 02/06/2011 03:57 PM, Simon Horman wrote:
>> On Sun, Feb 06, 2011 at 05:41:08PM +0200, Ahmed S. Darwish wrote:
>>> (Also applicable over 2.6.38-rc3)
>>>
>>> Had to explore two C code files to make sense of the 'crashkernel='
>>> kernel parameter values. Improve the situation.
>>>
>>> Signed-off-by: Ahmed S. Darwish <[email protected]>
>>> ---
>>>
>>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>>> index 89835a4..8f26b42 100644
>>> --- a/Documentation/kernel-parameters.txt
>>> +++ b/Documentation/kernel-parameters.txt
>>> @@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
>>> Format:
>>> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
>>>
>>> - crashkernel=nn[KMG]@ss[KMG]
>>> - [KNL] Reserve a chunk of physical memory to
>>> - hold a kernel to switch to with kexec on panic.
>>> + crashkernel=size[KMG][@offset[KMG]]
>>> + [KNL] Using kexec, Linux can switch to a 'crash kernel'
>>> + upon panic. This parameter reserves the physical
>>> + memory region [offset, offset + size] for that kernel
>>> + image. If the '@offset' part was ignored, Linux finds
>>> + a suitable crash image start address automatically.
>>
>> I think this would be further improved as:
>>
>> ... If '@offset' is omitted then a suitable
>> offset is selected automatically.
>
> Suitable offset as in parses a known image type (ELF, bzImage, etc) to
> find the start address? Or just assumes the entry point and load
> address are the same?
Neither. Suitable as in an offset that is naturally aligned for the
size up to I think 16MB where the kernel doesn't care anymore. Saying
that somewhere would be good but I don't think the definition of
suitable belongs in a reference doc like kernel-parameters.txt
The important things for users is to know that they don't need to
specify offset anymore.
> Is this the size for just the kernel image, or also for the physical
> memory it uses so it won't overwrite the existing kernel's stuff on the
> way up? (If a compressed kernel wants to decompress itself or extract
> an initramfs for itself, what happens?)
The size is the size of the area reserved for the crash capture kernel to run
in. The crash capture kernel never uses anything else.
All of the parsing etc is done in user space via /sbin/kexec.
Eric
On Sun, Feb 06, 2011 at 08:25:20PM -0600, Rob Landley wrote:
> On 02/06/2011 03:57 PM, Simon Horman wrote:
> > On Sun, Feb 06, 2011 at 05:41:08PM +0200, Ahmed S. Darwish wrote:
> >> (Also applicable over 2.6.38-rc3)
> >>
> >> Had to explore two C code files to make sense of the 'crashkernel='
> >> kernel parameter values. Improve the situation.
> >>
> >> Signed-off-by: Ahmed S. Darwish <[email protected]>
> >> ---
> >>
> >> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> >> index 89835a4..8f26b42 100644
> >> --- a/Documentation/kernel-parameters.txt
> >> +++ b/Documentation/kernel-parameters.txt
> >> @@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
> >> Format:
> >> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
> >>
> >> - crashkernel=nn[KMG]@ss[KMG]
> >> - [KNL] Reserve a chunk of physical memory to
> >> - hold a kernel to switch to with kexec on panic.
> >> + crashkernel=size[KMG][@offset[KMG]]
> >> + [KNL] Using kexec, Linux can switch to a 'crash kernel'
> >> + upon panic. This parameter reserves the physical
> >> + memory region [offset, offset + size] for that kernel
> >> + image. If the '@offset' part was ignored, Linux finds
> >> + a suitable crash image start address automatically.
> >
> > I think this would be further improved as:
> >
> > ... If '@offset' is omitted then a suitable
> > offset is selected automatically.
>
> Suitable offset as in parses a known image type (ELF, bzImage, etc) to
> find the start address? Or just assumes the entry point and load
> address are the same?
As in it finds a large enough area of contiguous free memory.
I believe that originally it searched from the bottom of memory,
it may be slightly smarter now.
Suitable is perhaps too strong a term.
In terms of the start address. On x86 at least it used to be
important to make sure that the start address matched but
these days using a relocatable kernel is an easier option.
> Is this the size for just the kernel image, or also for the physical
> memory it uses so it won't overwrite the existing kernel's stuff on the
> way up? (If a compressed kernel wants to decompress itself or extract
> an initramfs for itself, what happens?)
It is the memory that is used by the crash-kernel to avoid overwriting
the first-kernel's stuff. It is not the memory where the (usually
compressed) second-kernel is stored before it is kexeced.
If a compressed crash-kernel wants to decompress itself it does so in the
available memory which is the region reserved by the crash-kernel parameter
to the first-kernel.
On Mon, 7 Feb 2011 06:57:33 +0900 Simon Horman wrote:
> On Sun, Feb 06, 2011 at 05:41:08PM +0200, Ahmed S. Darwish wrote:
> > (Also applicable over 2.6.38-rc3)
> >
> > Had to explore two C code files to make sense of the 'crashkernel='
> > kernel parameter values. Improve the situation.
> >
> > Signed-off-by: Ahmed S. Darwish <[email protected]>
> > ---
> >
> > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> > index 89835a4..8f26b42 100644
> > --- a/Documentation/kernel-parameters.txt
> > +++ b/Documentation/kernel-parameters.txt
> > @@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
> > Format:
> > <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
> >
> > - crashkernel=nn[KMG]@ss[KMG]
> > - [KNL] Reserve a chunk of physical memory to
> > - hold a kernel to switch to with kexec on panic.
> > + crashkernel=size[KMG][@offset[KMG]]
> > + [KNL] Using kexec, Linux can switch to a 'crash kernel'
> > + upon panic. This parameter reserves the physical
> > + memory region [offset, offset + size] for that kernel
> > + image. If the '@offset' part was ignored, Linux finds
> > + a suitable crash image start address automatically.
>
> I think this would be further improved as:
>
> ... If '@offset' is omitted then a suitable
> offset is selected automatically.
>
> >
> > crashkernel=range1:size1[,range2:size2,...][@offset]
> > [KNL] Same as above, but depends on the memory
Hi,
I also prefer Simon's change. Can you please resend an updated patch?
thanks,
---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***
Had to explore two C code files to make sense of the 'crashkernel='
kernel parameter values. Improve the situation.
Signed-off-by: Ahmed S. Darwish <[email protected]>
---
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 89835a4..5ad9980 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
Format:
<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
- crashkernel=nn[KMG]@ss[KMG]
- [KNL] Reserve a chunk of physical memory to
- hold a kernel to switch to with kexec on panic.
+ crashkernel=size[KMG][@offset[KMG]]
+ [KNL] Using kexec, Linux can switch to a 'crash kernel'
+ upon panic. This parameter reserves the physical
+ memory region [offset, offset + size] for that kernel
+ image. If '@offset' is omitted, then a suitable offset
+ is selected automatically.
crashkernel=range1:size1[,range2:size2,...][@offset]
[KNL] Same as above, but depends on the memory
--
Darwish
http://darwish.07.googlepages.com
On Mon, Feb 07, 2011 at 01:30:54PM +0200, Ahmed S. Darwish wrote:
>
> Had to explore two C code files to make sense of the 'crashkernel='
> kernel parameter values. Improve the situation.
>
> Signed-off-by: Ahmed S. Darwish <[email protected]>
Thanks, that looks looks a good improvement over the existing documentation.
Acked-by: Simon Horman <[email protected]>
> ---
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 89835a4..5ad9980 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
> Format:
> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
>
> - crashkernel=nn[KMG]@ss[KMG]
> - [KNL] Reserve a chunk of physical memory to
> - hold a kernel to switch to with kexec on panic.
> + crashkernel=size[KMG][@offset[KMG]]
> + [KNL] Using kexec, Linux can switch to a 'crash kernel'
> + upon panic. This parameter reserves the physical
> + memory region [offset, offset + size] for that kernel
> + image. If '@offset' is omitted, then a suitable offset
> + is selected automatically.
>
> crashkernel=range1:size1[,range2:size2,...][@offset]
> [KNL] Same as above, but depends on the memory
>
> --
> Darwish
> http://darwish.07.googlepages.com
>
On Mon, Feb 07, 2011 at 01:30:54PM +0200, Ahmed S. Darwish wrote:
>
> Had to explore two C code files to make sense of the 'crashkernel='
> kernel parameter values. Improve the situation.
>
Did you look at Documentation/kdump/kdump.txt before looking into the
code. I thought kdump.txt explained the meaning of crashkernel= well.
In case if it was not obivious that for further details look into
kdump.txt, I will suggest to add a line asking reader to look into
kdump.txt for more details.
Tough crashkernel= range1:size1[,range2:size2,...][@offset], description
in next line already mentions kdump.txt
This patch looks good to me as it is though.
Acked-by: Vivek Goyal <[email protected]>
Vivek
> Signed-off-by: Ahmed S. Darwish <[email protected]>
> ---
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 89835a4..5ad9980 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
> Format:
> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
>
> - crashkernel=nn[KMG]@ss[KMG]
> - [KNL] Reserve a chunk of physical memory to
> - hold a kernel to switch to with kexec on panic.
> + crashkernel=size[KMG][@offset[KMG]]
> + [KNL] Using kexec, Linux can switch to a 'crash kernel'
> + upon panic. This parameter reserves the physical
> + memory region [offset, offset + size] for that kernel
> + image. If '@offset' is omitted, then a suitable offset
> + is selected automatically.
>
> crashkernel=range1:size1[,range2:size2,...][@offset]
> [KNL] Same as above, but depends on the memory
>
> --
> Darwish
> http://darwish.07.googlepages.com
On Mon, Feb 07, 2011 at 11:42:38AM +0900, Simon Horman wrote:
> On Sun, Feb 06, 2011 at 08:25:20PM -0600, Rob Landley wrote:
> > On 02/06/2011 03:57 PM, Simon Horman wrote:
> > > On Sun, Feb 06, 2011 at 05:41:08PM +0200, Ahmed S. Darwish wrote:
> > >> (Also applicable over 2.6.38-rc3)
> > >>
> > >> Had to explore two C code files to make sense of the 'crashkernel='
> > >> kernel parameter values. Improve the situation.
> > >>
> > >> Signed-off-by: Ahmed S. Darwish <[email protected]>
> > >> ---
> > >>
> > >> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> > >> index 89835a4..8f26b42 100644
> > >> --- a/Documentation/kernel-parameters.txt
> > >> +++ b/Documentation/kernel-parameters.txt
> > >> @@ -545,9 +545,12 @@ and is between 256 and 4096 characters. It is defined in the file
> > >> Format:
> > >> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
> > >>
> > >> - crashkernel=nn[KMG]@ss[KMG]
> > >> - [KNL] Reserve a chunk of physical memory to
> > >> - hold a kernel to switch to with kexec on panic.
> > >> + crashkernel=size[KMG][@offset[KMG]]
> > >> + [KNL] Using kexec, Linux can switch to a 'crash kernel'
> > >> + upon panic. This parameter reserves the physical
> > >> + memory region [offset, offset + size] for that kernel
> > >> + image. If the '@offset' part was ignored, Linux finds
> > >> + a suitable crash image start address automatically.
> > >
> > > I think this would be further improved as:
> > >
> > > ... If '@offset' is omitted then a suitable
> > > offset is selected automatically.
> >
> > Suitable offset as in parses a known image type (ELF, bzImage, etc) to
> > find the start address? Or just assumes the entry point and load
> > address are the same?
>
> As in it finds a large enough area of contiguous free memory.
> I believe that originally it searched from the bottom of memory,
> it may be slightly smarter now.
Now it has been changed to search from top of the memory (atleast for x86) and
that caused few troubles. On 32bit it searches for memory under 512MB and
on x86_64, it searches for memory under 896MB.
Though hpa had suggested to enhance the command line syntax such that a
user specifies the upper bound on memory. Something like crashkernel=x < y.
So reserve X amount of memory below y MB. It boils down to same thing
that somebody has to know that what is the maximum physical memory
locaton kernel can boot from.
I think it is dependent on kernel as well as dependent on kexec-tools. I
am wondering if it is possible to make this info part of bzImage protocol
where kernel tells bootloader the maximum physical memory kernel can be
loaded at. I think this is off topic in the context of this patch, just
a thought...
Thanks
Vivek
On Mon, Feb 07, 2011 at 09:25:50AM -0500, Vivek Goyal wrote:
> On Mon, Feb 07, 2011 at 01:30:54PM +0200, Ahmed S. Darwish wrote:
> >
> > Had to explore two C code files to make sense of the 'crashkernel='
> > kernel parameter values. Improve the situation.
> >
>
> Did you look at Documentation/kdump/kdump.txt before looking into the
> code. I thought kdump.txt explained the meaning of crashkernel= well.
>
> In case if it was not obivious that for further details look into
> kdump.txt, I will suggest to add a line asking reader to look into
> kdump.txt for more details.
>
Yes, I jumped to the code first :-) Here's a new patch with the link:
(Also applicable over latest -rc3)
==>
Complete the crashkernel= kernel parameter documentation.
Signed-off-by: Ahmed S. Darwish <[email protected]>
---
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 89835a4..050b0e5 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -545,16 +545,20 @@ and is between 256 and 4096 characters. It is defined in the file
Format:
<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
- crashkernel=nn[KMG]@ss[KMG]
- [KNL] Reserve a chunk of physical memory to
- hold a kernel to switch to with kexec on panic.
+ crashkernel=size[KMG][@offset[KMG]]
+ [KNL] Using kexec, Linux can switch to a 'crash kernel'
+ upon panic. This parameter reserves the physical
+ memory region [offset, offset + size] for that kernel
+ image. If '@offset' is omitted, then a suitable offset
+ is selected automatically. Check
+ Documentation/kdump/kdump.txt for further details.
crashkernel=range1:size1[,range2:size2,...][@offset]
[KNL] Same as above, but depends on the memory
in the running system. The syntax of range is
start-[end] where start and end are both
a memory unit (amount[KMG]). See also
- Documentation/kdump/kdump.txt for a example.
+ Documentation/kdump/kdump.txt for an example.
cs89x0_dma= [HW,NET]
Format: <dma>
>
> Acked-by: Vivek Goyal <[email protected]>
>
thanks,
--
Darwish
http://darwish.07.googlepages.com
On Mon, 7 Feb 2011 18:01:27 +0200 Ahmed S. Darwish wrote:
> On Mon, Feb 07, 2011 at 09:25:50AM -0500, Vivek Goyal wrote:
> > On Mon, Feb 07, 2011 at 01:30:54PM +0200, Ahmed S. Darwish wrote:
> > >
> > > Had to explore two C code files to make sense of the 'crashkernel='
> > > kernel parameter values. Improve the situation.
> > >
> >
> > Did you look at Documentation/kdump/kdump.txt before looking into the
> > code. I thought kdump.txt explained the meaning of crashkernel= well.
> >
> > In case if it was not obivious that for further details look into
> > kdump.txt, I will suggest to add a line asking reader to look into
> > kdump.txt for more details.
> >
>
> Yes, I jumped to the code first :-) Here's a new patch with the link:
>
> (Also applicable over latest -rc3)
>
> ==>
>
> Complete the crashkernel= kernel parameter documentation.
>
> Signed-off-by: Ahmed S. Darwish <[email protected]>
> ---
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 89835a4..050b0e5 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -545,16 +545,20 @@ and is between 256 and 4096 characters. It is defined in the file
> Format:
> <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
>
> - crashkernel=nn[KMG]@ss[KMG]
> - [KNL] Reserve a chunk of physical memory to
> - hold a kernel to switch to with kexec on panic.
> + crashkernel=size[KMG][@offset[KMG]]
> + [KNL] Using kexec, Linux can switch to a 'crash kernel'
> + upon panic. This parameter reserves the physical
> + memory region [offset, offset + size] for that kernel
> + image. If '@offset' is omitted, then a suitable offset
> + is selected automatically. Check
> + Documentation/kdump/kdump.txt for further details.
>
> crashkernel=range1:size1[,range2:size2,...][@offset]
> [KNL] Same as above, but depends on the memory
> in the running system. The syntax of range is
> start-[end] where start and end are both
> a memory unit (amount[KMG]). See also
> - Documentation/kdump/kdump.txt for a example.
> + Documentation/kdump/kdump.txt for an example.
>
> cs89x0_dma= [HW,NET]
> Format: <dma>
>
>
> >
> > Acked-by: Vivek Goyal <[email protected]>
Applied v3, along with your KMG info patch. Thanks.
---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***