This adds the documentation for the extended crashkernel syntax into
Documentation/kdump/kdump.txt.
Signed-off-by: Bernhard Walle <[email protected]>
---
Documentation/kdump/kdump.txt | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
--- a/Documentation/kdump/kdump.txt
+++ b/Documentation/kdump/kdump.txt
@@ -231,6 +231,32 @@ Dump-capture kernel config options (Arch
any space below the alignment point will be wasted.
+Extended crashkernel syntax
+===========================
+
+While the "crashkernel=size[@offset]" syntax is sufficient for most
+configurations, sometimes it's handy to have the reserved memory dependent
+on the value of System RAM -- that's mostly for distributors that pre-setup
+the kernel command line to avoid a unbootable system after some memory has
+been removed from the machine.
+
+The syntax is:
+
+ crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
+ range=start-[end]
+
+For example:
+
+ crashkernel=512M-2G:64M,2G-:128M
+
+This would mean:
+
+ 1) if the RAM is smaller than 512M, then don't reserve anything
+ (this is the "rescue" case)
+ 2) if the RAM size is between 512M and 2G, then reserve 64M
+ 3) if the RAM size is larger than 2G, then reserve 128M
+
+
Boot into System Kernel
=======================
--
Hi!
> This adds the documentation for the extended crashkernel syntax into
> Documentation/kdump/kdump.txt.
Should you also update kernel-parameters.txt?
> +For example:
> +
> + crashkernel=512M-2G:64M,2G-:128M
> +
> +This would mean:
> +
> + 1) if the RAM is smaller than 512M, then don't reserve anything
> + (this is the "rescue" case)
> + 2) if the RAM size is between 512M and 2G, then reserve 64M
> + 3) if the RAM size is larger than 2G, then reserve 128M
Why is this useful? I mean... if 64M is enough to save a dump, why use
128M? ...or does the required size somehow scale with memory in
machine? (pagetables?)
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
* Pavel Machek <[email protected]> [2007-09-18 19:21]:
> > This adds the documentation for the extended crashkernel syntax into
> > Documentation/kdump/kdump.txt.
>
> Should you also update kernel-parameters.txt?
Ok, I'll do.
> > +For example:
> > +
> > + crashkernel=512M-2G:64M,2G-:128M
> > +
> > +This would mean:
> > +
> > + 1) if the RAM is smaller than 512M, then don't reserve anything
> > + (this is the "rescue" case)
> > + 2) if the RAM size is between 512M and 2G, then reserve 64M
> > + 3) if the RAM size is larger than 2G, then reserve 128M
>
> Why is this useful? I mean... if 64M is enough to save a dump, why use
> 128M? ...or does the required size somehow scale with memory in
> machine? (pagetables?)
A bit, yes (ELF core headers, DISCONT memory, per-CPU data), but
consider also that saving may be faster if you have more RAM (e.g.
saving over SSH, encryption, ...).
Thanks,
Bernhard