> -----Original Message----- > From: linux-ia64-owner@xxxxxxxxxxxxxxx > [mailto:linux-ia64-owner@xxxxxxxxxxxxxxx] On Behalf Of Zou, Nanhai > Sent: 2007年2月6日 9:09 > To: Horms; fastboot@xxxxxxxxxxxxxx; linux-ia64@xxxxxxxxxxxxxxx > Cc: Khalid Aziz; Mel Gorman; Bob Picco; Magnus Damm > Subject: RE: Zero size /proc/vmcore on ia64 > > > This seems to be a corner case which purgatory efi-memmap code does not handle > correctly. > > Can you print the memory ranges layout information of first and second kernel? > e.g, the efi memmap, the crash notes memory address. > > Thanks > Zou Nan hai > > > -----Original Message----- > > From: Horms [mailto:horms@xxxxxxxxxxxx] > > Sent: 2007年2月5日 9:59 > > To: fastboot@xxxxxxxxxxxxxx; linux-ia64@xxxxxxxxxxxxxxx > > Cc: Zou, Nanhai; Khalid Aziz; Mel Gorman; Bob Picco; Magnus Damm > > Subject: Zero size /proc/vmcore on ia64 > > > > Hi, > > > > I have been poking around this problem a bit over the past week, > > and I thought it would be a good idea to get it out in the open. > > > > At some stage /proc/vmcore (in a crash-kernel) went from being > > something useful, to being zero size. > > > > I initially thought this was because saved_max_pfn was not being > > set correctly. And indeed it is not set for discontig memory. > > But the trivial fix below has not been sufficient to resolve the problem :( > > > > The problem seems to be along the lines of: > > * kexec-tool sets up a segment to contain the elf header. > > * This segment happens to be almost at the end of the crashkernel area > > of memory that is visible to the crash kernel. > > * However, when purgatory munges the EFI map, this segment > > is marked as EFI_UNUSABLE_MEMORY. > > * As a result of this it is not in a range covered by efi_memmap_walk() > > * And thus it is outside the range of memory covered by a valid PFN > > (remember its at the end of memory, it turns out that the > > max PFN covers memory up until just before the header) > > * The header can't be read by the vmcore setup code > > * And vmcore is uninitialised > > > > read_from_oldmem: error: pfn (32761) > saved_max_pfn (31744) > > Kdump: vmcore not initialized > > > > The saved_max_pfn error above is produced by debuging code > > that I added to read_from_oldmem(). > > It also uses the patch below, otherwise saved_max_pfn is 0. > > > > For reference: > > I am using today's linus tree (2.6.20) > > The problem seems to have been around since at least 2.6.19-rc6 > > I have a Tiger2 system using disctontig memory > > The problem also seems to manifest when using contig memory > > > > -- > > Horms > > H: http://www.vergenet.net/~horms/ > > W: http://www.valinux.co.jp/en/ > > > > Set saved_max_pfn when discontig memory is in use. > > > > This sets up saved_max_pfn when disctontig memory is in use. > > This mirrors the code for contig memory. > > > > This patch does not entirely solve the problem of making vmcore work, > > however it does appear to be neccessary. Please consider applying. > > > > Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx> > > > > diff --git a/arch/ia64/mm/discontig.c b/arch/ia64/mm/discontig.c > > index 96722cb..999cefd 100644 > > --- a/arch/ia64/mm/discontig.c > > +++ b/arch/ia64/mm/discontig.c > > @@ -506,6 +509,12 @@ void __init find_memory(void) > > max_pfn = max_low_pfn; > > > > find_initrd(); > > + > > +#ifdef CONFIG_CRASH_DUMP > > + /* If we are doing a crash dump, we still need to know the real mem > > + * size before original memory map is reset. */ > > + saved_max_pfn = max_pfn; > > +#endif > > } > > > > #ifdef CONFIG_SMP Hi Vivek, I have a question about why saved_max_pfn check in vmcore.c is needed. Here is a typical memory layout of IA64 machine. ----- ===>max_pfn for first kernel the first kernel ----- ===>max_pfn for crash dump kernel the crash dump kernel ----- the first kernel ----- When crash dump kernel tries to access memory of first kernel above saved_max_pfn of him, read_from_oldmem will refuse that read. That result an empty vmcore file. change saved_max_pfn to unsigned long(-1) will fix this issue. However since memory ranges in vmcore is pre defined from /proc/iomem of first kernel, why do we still need to add an extra check in vmcore.c Thanks Zou Nan hai - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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