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

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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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > Cc: Marc Zyngier <maz@xxxxxxxxxx>
> > Cc: Steven Price <steven.price@xxxxxxx>
> > [catalin.marinas@xxxxxxx: added flag preserving in __split_huge_page_tail()]
> > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> > ---
> >  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",



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