Messages in this thread | | | Subject | Re: [PATCH 0/5] Add second memory region for crash kernel | From | (Eric W. Biederman) | Date | Thu, 22 Apr 2010 17:48:53 -0700 |
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Vivek Goyal <vgoyal@redhat.com> writes:
> On Thu, Apr 22, 2010 at 03:07:11PM -0700, Eric W. Biederman wrote: >> Vitaly Mayatskikh <v.mayatskih@gmail.com> writes: >> > >> > This serie of patches realizes this approach. It requires also changes >> > in kexec utility to make this feature work, but is >> > backward-compatible: old versions of kexec will work with new >> > kernel. I will post patch to kexec-tools upstream separately. >> >> Have you tried loading a 64bit vmlinux directly into a higher address >> range? There may be a bit or two missing but you should be able to >> load a linux kernel above 4GB. I tested the basics of that mechanism >> when I made the 64bit relocatable kernel. > > I guess even if it works, for distributions it will become additional > liability to carry vmlinux (instead of relocatable bzImage). So we shall > have to find a way to make bzImage work.
As Peter pointed out we actually have everything thing we need except a bit of documentation and the flag that says this is a 64bit kernel.
From a testing perspective a 64bit vmlinux should work today without changes. Once it is confirmed there is a solution with the 64bit kernel we just need a small patch to boot.txt and a few tweaks to /sbin/kexec to handle a 64bit bzImage.
>> I don't buy the argument that there is a direct connection between >> the amount of memory you have and how much memory it takes to dump it. >> Even an indirect connections seems suspicious. > > Memory requirement by user space might be of interest though like dump > filtering tools. I vaguely remember that it used to first traverse all > the memory pages, create some internal data structures and then start > dumping. > > So memory required by filtering tool might be directly proportional to > amount of memory present in the system.
Assuming your dump filtering tool creates a bitmap of pages to be dumped you get a ration of 32K to 1. Or 3MB for 100GB and 32MB for 1TB. Which is noticeable in the worst case but definitely not enough to push us past 2GB.
> Vitaly, have you really run into cases where 2G upper limit is a concern. > What is the configuration you have, how much memory it has and how much > memory are you planning to reserve for kdump kernel?
A good question.
Eric
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