Save PG_compound or PG_head value in VMCOREINFO

[Eric W. Biederman]

Petr Tesarik <ptesarik at suse.cz> writes:

> To allow filtering of huge pages, makedumpfile must be able to identify
> them in the dump. This can be done by checking for the appropriate
> page flag, so communicate its value to makedumpfile through the VMCOREINFO 
> interface.

I don't have any siginificant problems with exporting this information.
However that #ifddef looks nasty and confusing.

Does that #ifdef exist in the huge page code as well?

Can we always export both?  Can we only export one?

What is the purpose of the #ifdef?

As it stands that looks like code that will figure out how to bitrot
if we just leave it sitting there.

> Signed-off-by: Petr Tesarik <ptesarik at suse.cz>
>
> ---
>  kernel/kexec.c |    5 +++++
>  1 file changed, 5 insertions(+)
>
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -1511,6 +1511,11 @@ static int __init crash_save_vmcoreinfo_
>  	VMCOREINFO_NUMBER(NR_FREE_PAGES);
>  	VMCOREINFO_NUMBER(PG_lru);
>  	VMCOREINFO_NUMBER(PG_private);
> +#ifdef CONFIG_PAGEFLAGS_EXTENDED
> +	VMCOREINFO_NUMBER(PG_head);
> +#else
> +	VMCOREINFO_NUMBER(PG_compound);
> +#endif
>  	VMCOREINFO_NUMBER(PG_swapcache);
>  
>  	arch_crash_save_vmcoreinfo();