Re: [patch 2/2] [PATCH] mm: Save soft-dirty bits on file pages

[Cyrill Gorcunov <gorcunov@gmail.com>]

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On Wed, Aug 07, 2013 at 01:28:12PM -0700, Andrew Morton wrote:
> 
> Good god.
> 
> I wonder if these can be turned into out-of-line functions in some form
> which humans can understand.
> 
> or
> 
> #define pte_to_pgoff(pte)
> 	frob(pte, PTE_FILE_SHIFT1, PTE_FILE_BITS1) +
> 	frob(PTE_FILE_SHIFT2, PTE_FILE_BITS2) +
> 	frob(PTE_FILE_SHIFT3, PTE_FILE_BITS3) +
> 	frob(PTE_FILE_SHIFT4, PTE_FILE_BITS1 + PTE_FILE_BITS2 + PTE_FILE_BITS3)

Hi, here is what I ended up with. Please take a look (I decided to post
patch in the thread since it's related to the context of the mails).

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From: Cyrill Gorcunov <gorcunov@gmail.com>
Subject: mm: Cleanup pte_to_pgoff and pgoff_to_pte helpers

Andrew asked if there a way to make pte_to_pgoff
and pgoff_to_pte macro helpers somehow more readable.

With this patch it should be more understandable what
is happening with bits when they come to and from pte
entry.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
---

Guys, is there a reason for "if _PAGE_BIT_FILE < _PAGE_BIT_PROTNONE"
test present in this pgtable-2level.h file at all? I can't imagine
where it can be false on x86.

 arch/x86/include/asm/pgtable-2level.h |   82 +++++++++++++++++-----------------
 1 file changed, 41 insertions(+), 41 deletions(-)

Index: linux-2.6.git/arch/x86/include/asm/pgtable-2level.h
===================================================================
--- linux-2.6.git.orig/arch/x86/include/asm/pgtable-2level.h
+++ linux-2.6.git/arch/x86/include/asm/pgtable-2level.h
@@ -55,6 +55,9 @@ static inline pmd_t native_pmdp_get_and_
 #define native_pmdp_get_and_clear(xp) native_local_pmdp_get_and_clear(xp)
 #endif
 
+#define _mfrob(v,r,m,l)		((((v) >> (r)) & (m)) << (l))
+#define __frob(v,r,l)		(((v) >> (r)) << (l))
+
 #ifdef CONFIG_MEM_SOFT_DIRTY
 
 /*
@@ -71,31 +74,27 @@ static inline pmd_t native_pmdp_get_and_
 #define PTE_FILE_BITS2		(PTE_FILE_SHIFT3 - PTE_FILE_SHIFT2 - 1)
 #define PTE_FILE_BITS3		(PTE_FILE_SHIFT4 - PTE_FILE_SHIFT3 - 1)
 
-#define pte_to_pgoff(pte)						\
-	((((pte).pte_low >> (PTE_FILE_SHIFT1))				\
-	  & ((1U << PTE_FILE_BITS1) - 1)))				\
-	+ ((((pte).pte_low >> (PTE_FILE_SHIFT2))			\
-	    & ((1U << PTE_FILE_BITS2) - 1))				\
-	   << (PTE_FILE_BITS1))						\
-	+ ((((pte).pte_low >> (PTE_FILE_SHIFT3))			\
-	    & ((1U << PTE_FILE_BITS3) - 1))				\
-	   << (PTE_FILE_BITS1 + PTE_FILE_BITS2))			\
-	+ ((((pte).pte_low >> (PTE_FILE_SHIFT4)))			\
-	    << (PTE_FILE_BITS1 + PTE_FILE_BITS2 + PTE_FILE_BITS3))
-
-#define pgoff_to_pte(off)						\
-	((pte_t) { .pte_low =						\
-	 ((((off)) & ((1U << PTE_FILE_BITS1) - 1)) << PTE_FILE_SHIFT1)	\
-	 + ((((off) >> PTE_FILE_BITS1)					\
-	     & ((1U << PTE_FILE_BITS2) - 1))				\
-	    << PTE_FILE_SHIFT2)						\
-	 + ((((off) >> (PTE_FILE_BITS1 + PTE_FILE_BITS2))		\
-	     & ((1U << PTE_FILE_BITS3) - 1))				\
-	    << PTE_FILE_SHIFT3)						\
-	 + ((((off) >>							\
-	      (PTE_FILE_BITS1 + PTE_FILE_BITS2 + PTE_FILE_BITS3)))	\
-	    << PTE_FILE_SHIFT4)						\
-	 + _PAGE_FILE })
+#define PTE_FILE_MASK1		((1U << PTE_FILE_BITS1) - 1)
+#define PTE_FILE_MASK2		((1U << PTE_FILE_BITS2) - 1)
+#define PTE_FILE_MASK3		((1U << PTE_FILE_BITS3) - 1)
+
+#define PTE_FILE_LSHIFT2	(PTE_FILE_BITS1)
+#define PTE_FILE_LSHIFT3	(PTE_FILE_BITS1 + PTE_FILE_BITS2)
+#define PTE_FILE_LSHIFT4	(PTE_FILE_BITS1 + PTE_FILE_BITS2 + PTE_FILE_BITS3)
+
+#define pte_to_pgoff(pte)							    \
+	(_mfrob((pte).pte_low, PTE_FILE_SHIFT1, PTE_FILE_MASK1, 0)		  + \
+	 _mfrob((pte).pte_low, PTE_FILE_SHIFT2, PTE_FILE_MASK2, PTE_FILE_LSHIFT2) + \
+	 _mfrob((pte).pte_low, PTE_FILE_SHIFT3, PTE_FILE_MASK3, PTE_FILE_LSHIFT3) + \
+	 __frob((pte).pte_low, PTE_FILE_SHIFT4, PTE_FILE_LSHIFT4))
+
+#define pgoff_to_pte(off)							\
+	((pte_t) { .pte_low =							\
+	_mfrob(off,                0, PTE_FILE_MASK1, PTE_FILE_SHIFT1)	+	\
+	_mfrob(off, PTE_FILE_LSHIFT2, PTE_FILE_MASK2, PTE_FILE_SHIFT2)	+	\
+	_mfrob(off, PTE_FILE_LSHIFT3, PTE_FILE_MASK3, PTE_FILE_SHIFT3)	+	\
+	__frob(off, PTE_FILE_LSHIFT4, PTE_FILE_SHIFT4)			+	\
+	_PAGE_FILE })
 
 #else /* CONFIG_MEM_SOFT_DIRTY */
 
@@ -115,22 +114,23 @@ static inline pmd_t native_pmdp_get_and_
 #define PTE_FILE_BITS1		(PTE_FILE_SHIFT2 - PTE_FILE_SHIFT1 - 1)
 #define PTE_FILE_BITS2		(PTE_FILE_SHIFT3 - PTE_FILE_SHIFT2 - 1)
 
-#define pte_to_pgoff(pte)						\
-	((((pte).pte_low >> PTE_FILE_SHIFT1)				\
-	  & ((1U << PTE_FILE_BITS1) - 1))				\
-	 + ((((pte).pte_low >> PTE_FILE_SHIFT2)				\
-	     & ((1U << PTE_FILE_BITS2) - 1)) << PTE_FILE_BITS1)		\
-	 + (((pte).pte_low >> PTE_FILE_SHIFT3)				\
-	    << (PTE_FILE_BITS1 + PTE_FILE_BITS2)))
-
-#define pgoff_to_pte(off)						\
-	((pte_t) { .pte_low =						\
-	 (((off) & ((1U << PTE_FILE_BITS1) - 1)) << PTE_FILE_SHIFT1)	\
-	 + ((((off) >> PTE_FILE_BITS1) & ((1U << PTE_FILE_BITS2) - 1))	\
-	    << PTE_FILE_SHIFT2)						\
-	 + (((off) >> (PTE_FILE_BITS1 + PTE_FILE_BITS2))		\
-	    << PTE_FILE_SHIFT3)						\
-	 + _PAGE_FILE })
+#define PTE_FILE_MASK1		((1U << PTE_FILE_BITS1) - 1)
+#define PTE_FILE_MASK2		((1U << PTE_FILE_BITS2) - 1)
+
+#define PTE_FILE_LSHIFT2	(PTE_FILE_BITS1)
+#define PTE_FILE_LSHIFT3	(PTE_FILE_BITS1 + PTE_FILE_BITS2)
+
+#define pte_to_pgoff(pte)							    \
+	(_mfrob((pte).pte_low, PTE_FILE_SHIFT1, PTE_FILE_MASK1, 0)		  + \
+	 _mfrob((pte).pte_low, PTE_FILE_SHIFT2, PTE_FILE_MASK2, PTE_FILE_LSHIFT2) + \
+	 __frob((pte).pte_low, PTE_FILE_SHIFT3, PTE_FILE_LSHIFT3))
+
+#define pgoff_to_pte(off)							\
+	((pte_t) { .pte_low =							\
+	_mfrob(off,                0, PTE_FILE_MASK1, PTE_FILE_SHIFT1)	+	\
+	_mfrob(off, PTE_FILE_LSHIFT2, PTE_FILE_MASK2, PTE_FILE_SHIFT2)	+	\
+	__frob(off, PTE_FILE_LSHIFT3, PTE_FILE_SHIFT3)			+	\
+	_PAGE_FILE })
 
 #endif /* CONFIG_MEM_SOFT_DIRTY */