On Wed, Sep 10, 2008 at 09:17:10AM -0400, Vivek Goyal wrote: > On Wed, Sep 10, 2008 at 03:40:45PM +0900, Magnus Damm wrote: > > On Mon, Sep 8, 2008 at 10:04 PM, Vivek Goyal <vgoyal at redhat.com> wrote: > > > On Mon, Sep 08, 2008 at 12:21:32PM +0900, Magnus Damm wrote: > > >> From: Magnus Damm <damm at igel.co.jp> > > >> > > >> This patch removes the saved_max_pfn check from the /proc/vmcore > > >> function read_from_oldmem(). No need to verify, we should be able > > >> to just trust that "elfcorehdr=" is correctly passed to the crash > > >> kernel on the kernel command line like we do with other parameters. > > >> > > >> The read_from_oldmem() function in fs/proc/vmcore.c is quite similar > > >> to read_from_oldmem() in drivers/char/mem.c, but only in the latter > > >> it makes sense to use saved_max_pfn. For oldmem it is used to determine > > >> when to stop reading. For vmcore we already have the elf header info > > >> pointing out the physical memory regions, no need to pass the end-of- > > >> old-memory twice. > > >> > > >> Removing the saved_max_pfn check from vmcore makes it possible for > > >> architectures to skip oldmem but still support crash dump through > > >> vmcore - without the need for the old saved_max_pfn cruft. > > >> > > >> Architectures that want to play safe can do the saved_max_pfn check > > >> in copy_oldmem_page(). Not sure why anyone would want to do that, > > >> but that's even safer than today - the saved_max_pfn check in vmcore > > >> removed by this patch only checks the first page. > > > > Hi Vivek, > > > > > Though I don't feel very strongly for saved_max_pfn check in vmcore.c, > > > but at the same time I don't understand what are you gaining by removing > > > this check. Any way we are not getting rid of this symbol altogether > > > because /dev/oldmem needs it. > > > > Let me try to be a bit more clear. =) > > > > > Is it sh arch for which you want to disable /dev/oldmem and only enable > > > /proc/vmcore and hence want to get rid of saved_max_pfn? > > > > Yes, exactly. I could do as powerpc and just pass the saved_max_pfn on > > the command line together with the elfcorehdr pointer, but why? For > > vmcore we only need the elfcorehdr pointer. > > > > > Though I agree that we should elfcorehdrs but at the same time it does not > > > hard doing additional check (We are anyway carrying saved_max_pfn for > > > /dev/oldmem). We can always extend current code to check for end page also > > > to make sure we are not reading beyond saved_max_pfn. > > > > Maybe it doesn't harm, but it doesn't do any good either. Relying on > > saved_max_pfn just requires more architecture specific code. The > > existing vmcore.c code can of course be fixed up to handle the end > > page, but what is the exact point with using saved_max_pfn in > > vmcore.c? > > > > I understand it is needed for oldmem, so I'm not saying that we should > > remove the symbol all together. > > > > > How much code is it to set value of saved_max_pfn in sh that you want to > > > completely get rid of it. My feeling is that it should be just few lines. > > > > You are correct. We just need to add a kernel command line parameter > > and change kexec-tools to pass along that value. Like powerpc does > > today. I did of course do just that in my first iteration of crash > > support for SuperH and it works just fine. But why should we pass more > > information than we actually need? > > > > So it's not a matter of coding effort. It's more about passing just > > the information that is needed to the secondary kernel. And if we want > > to use vmcore but not oldmem, saved_max_pfn isn't needed. Unless I'm > > mistaken that is. =) > > > > > So though I don't feel strongly for saved_max_pfn check in vmcore.c, at > > > the same time I don't see you are gaining anything significant by removing > > > it. We can just introduce saved_max_pfn in sh also. > > > > Yep, we could introduce that on SuperH, but pruning code that is not > > really needed is a step in the right direction IMO. > > > > Hi Magnus, > > Ok, I can't think of a strong reason why should we retain saved_max_pfn > check in /proc/vmcore and it looks like elfcorehdr= should be equally > reliable. > > I have no objections to the patch. > > Acked-by: Vivek Goyal <vgoyal at redhat.com> Acked-by: Simon Horman <horms at verge.net.au> BTW, does anyone actually use /proc/oldmem ?
