V Tue, 27 Nov 2012 15:25:35 -0600 ebiederm at xmission.com (Eric W. Biederman) naps?no: > 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? For the huge page code, the #ifdef is constrained to include/linux/page-flags.h, which has two sets of functions depending on CONFIG_PAGEFLAGS_EXTENDED. The page flag which does exist in a given configuration is implemented directly using the standard page flag definitions, and the flags that do not exist are emulated with inline functions of the corresponding name. > Can we always export both? Can we only export one? Neither. Their existence is mutually exclusive, i.e.: CONFIG_PAGEFLAGS_EXTENDED -> PG_head, PG_tail, no PG_compound !CONFIG_PAGEFLAGS_EXTENDED -> PG_compound, no PG_head, no PG_tail All I can do is create a "virtual" page flag mask (e.g. PG_hugepage_mask), which is initialized either to 1L << PG_compound or to (1L << PG_head) | (1L << PG_tail). Such definition could then be kept in <linux/page-flags.h>. I'm not sure it's worth it, because there would be only one in-tree user of this new macro. > 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. It cannot simply bitrot and be silently wrong. If it ever gets out of sync with page-flags.h, this code won't even compile, because one or the other page flag is always missing. Petr Tesarik > > 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();
