Re: [PATCH v2 3/7] mm: Add PG_arch_3 page flag

Peter Collingbourne
2022-07-22T17:05:15Z

On Fri, Jul 22, 2022 at 03:16:34PM +0100, Marc Zyngier wrote:
> On Fri, 22 Jul 2022 02:50:29 +0100,
> Peter Collingbourne <pcc@google.com> wrote:
> >
> > As with PG_arch_2, this flag is only allowed on 64-bit architectures due
> > to the shortage of bits available. It will be used by the arm64 MTE code
> > in subsequent patches.
> >
> > Signed-off-by: Peter Collingbourne <pcc@google.com>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Steven Price <steven.price@arm.com>
> > [catalin.marinas@arm.com: added flag preserving in __split_huge_page_tail()]
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > ---
> > fs/proc/page.c | 1 +
> > include/linux/page-flags.h | 1 +
> > include/trace/events/mmflags.h | 7 ++++---
> > mm/huge_memory.c | 1 +
> > 4 files changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/proc/page.c b/fs/proc/page.c
> > index a2873a617ae8..438b8aa7249d 100644
> > --- a/fs/proc/page.c
> > +++ b/fs/proc/page.c
> > @@ -220,6 +220,7 @@ u64 stable_page_flags(struct page *page)
> > u |= kpf_copy_bit(k, KPF_ARCH, PG_arch_1);
> > #ifdef CONFIG_64BIT
> > u |= kpf_copy_bit(k, KPF_ARCH_2, PG_arch_2);
> > + u |= kpf_copy_bit(k, KPF_ARCH_2, PG_arch_3);
>
> Are PG_arch_2 and PG_arch_3 supposed to share the same user bit in
> /proc/kpageflags? This seems odd.

No, that was an oversight, thanks for the catch. I will fix it up like
so in v3.

Peter

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 438b8aa7249d..0129aa3cfb7a 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -220,7 +220,7 @@ u64 stable_page_flags(struct page *page)
u |= kpf_copy_bit(k, KPF_ARCH, PG_arch_1);
#ifdef CONFIG_64BIT
u |= kpf_copy_bit(k, KPF_ARCH_2, PG_arch_2);
- u |= kpf_copy_bit(k, KPF_ARCH_2, PG_arch_3);
+ u |= kpf_copy_bit(k, KPF_ARCH_3, PG_arch_3);
#endif

return u;
diff --git a/include/linux/kernel-page-flags.h b/include/linux/kernel-page-flags.h
index eee1877a354e..859f4b0c1b2b 100644
--- a/include/linux/kernel-page-flags.h
+++ b/include/linux/kernel-page-flags.h
@@ -18,5 +18,6 @@
#define KPF_UNCACHED 39
#define KPF_SOFTDIRTY 40
#define KPF_ARCH_2 41
+#define KPF_ARCH_3 42

#endif /* LINUX_KERNEL_PAGE_FLAGS_H */
diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index 381dcc00cb62..364373f5bba0 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -79,6 +79,7 @@
#define KPF_UNCACHED 39
#define KPF_SOFTDIRTY 40
#define KPF_ARCH_2 41
+#define KPF_ARCH_3 42

/* [47-] take some arbitrary free slots for expanding overloaded flags
* not part of kernel API
@@ -138,6 +139,7 @@ static const char * const page_flag_names[] = {
[KPF_UNCACHED] = "c:uncached",
[KPF_SOFTDIRTY] = "f:softdirty",
[KPF_ARCH_2] = "H:arch_2",
+ [KPF_ARCH_3] = "H:arch_3",

[KPF_ANON_EXCLUSIVE] = "d:anon_exclusive",
[KPF_READAHEAD] = "I:readahead",