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SubjectRe: [patch 2/2] [PATCH] mm: Save soft-dirty bits on file pages
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).
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 */
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