On Tue, Jul 27, 2021 at 7:18 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: > > On 7/14/21 2:17 AM, Muchun Song wrote: > > Introduce save_page_flags to return the page flags which can cooperate > > with show_page_flags. If we want to hihe some page flags from users, it > > will be useful to alter save_page_flags directly. This is a preparation > > for the next patch to hide some page flags from users. > > > > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> > > --- > > include/trace/events/mmflags.h | 3 +++ > > include/trace/events/page_ref.h | 8 ++++---- > > 2 files changed, 7 insertions(+), 4 deletions(-) > > > > diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h > > index 390270e00a1d..69cb84b1257e 100644 > > --- a/include/trace/events/mmflags.h > > +++ b/include/trace/events/mmflags.h > > @@ -121,6 +121,9 @@ IF_HAVE_PG_IDLE(PG_idle, "idle" ) \ > > IF_HAVE_PG_ARCH_2(PG_arch_2, "arch_2" ) \ > > IF_HAVE_PG_SKIP_KASAN_POISON(PG_skip_kasan_poison, "skip_kasan_poison") > > > > +#define save_page_flags(page) \ > > + (((page)->flags & ~PAGEFLAGS_MASK)) > > + > > Looking ahead to the next patch, this is changed to hide the PG_head > flag for 'fake' head pages. > > IIRC, all vmemmap pages except the first will be mapped read only. So, > all vmemmap pages with 'fake' head pages will be read only. > > It seems that all the modified trace events below are associated with > updates to page structs. Therefore, it seems these events will never > experience a 'fake' head page. Am I missing something? Totally right. I didn't realize this point before. We cannot see a fake page struct in page refcount tracing. So this patch is definitely pointless. I'll drop it in the next version. Thanks Mike. > > -- > Mike Kravetz
