[PATCH] mm/pageblock: throw compiling time error if pageblock_bits can not hold MIGRATE_TYPES

[PATCH] mm/pageblock: throw compiling time error if pageblock_bits can not hold MIGRATE_TYPES

[Pingfan Liu]

Currently, NR_PAGEBLOCK_BITS and MIGRATE_TYPES are not associated by code.
If someone adds extra migrate type, then he may forget to enlarge the
NR_PAGEBLOCK_BITS.
NR_PAGEBLOCK_BITS depends on MIGRATE_TYPES, while these macro
spread on two different .h file with reverse dependency, it is a little
hard to refer to MIGRATE_TYPES in pageblock-flag.h. This patch tries to
remind such relation in compiling-time.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
---
 include/linux/pageblock-flags.h | 5 +++--
 mm/page_alloc.c                 | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index 9132c5c..fe0aec4 100644
--- a/include/linux/pageblock-flags.h
+++ b/include/linux/pageblock-flags.h
@@ -25,11 +25,12 @@
 
 #include <linux/types.h>
 
+#define PB_migratetype_bits 3
 /* Bit indices that affect a whole block of pages */
 enum pageblock_bits {
 	PB_migrate,
-	PB_migrate_end = PB_migrate + 3 - 1,
-			/* 3 bits required for migrate types */
+	PB_migrate_end = PB_migrate + PB_migratetype_bits - 1,
+			/* n bits required for migrate types */
 	PB_migrate_skip,/* If set the block is skipped by compaction */
 
 	/*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2ec9cc4..537020f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -425,7 +425,7 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
 	unsigned long bitidx, word_bitidx;
 	unsigned long old_word, word;
 
-	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
+	BUILD_BUG_ON(order_base_2(MIGRATE_TYPES) != PB_migratetype_bits);
 
 	bitmap = get_pageblock_bitmap(page, pfn);
 	bitidx = pfn_to_bitidx(page, pfn);
-- 
2.7.4

Re: [PATCH] mm/pageblock: throw compiling time error if pageblock_bits can not hold MIGRATE_TYPES

[kbuild test robot]

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Hi Pingfan,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.20-rc5 next-20181206]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Pingfan-Liu/mm-pageblock-throw-compiling-time-error-if-pageblock_bits-can-not-hold-MIGRATE_TYPES/20181207-034245
config: x86_64-randconfig-x011-201848 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All error/warnings (new ones prefixed by >>):

   In file included from include/asm-generic/bug.h:5:0,
                    from arch/x86/include/asm/bug.h:47,
                    from include/linux/bug.h:5,
                    from include/linux/mmdebug.h:5,
                    from include/linux/mm.h:9,
                    from mm/page_alloc.c:18:
   mm/page_alloc.c: In function 'set_pfnblock_flags_mask':
>> include/linux/compiler.h:372:38: error: call to '__compiletime_assert_428' declared with attribute error: BUILD_BUG_ON failed: order_base_2(MIGRATE_TYPES) != PB_migratetype_bits
     _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                         ^
   include/linux/compiler.h:353:4: note: in definition of macro '__compiletime_assert'
       prefix ## suffix();    \
       ^~~~~~
   include/linux/compiler.h:372:2: note: in expansion of macro '_compiletime_assert'
     _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
     ^~~~~~~~~~~~~~~~~~~
   include/linux/build_bug.h:45:37: note: in expansion of macro 'compiletime_assert'
    #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                        ^~~~~~~~~~~~~~~~~~
   include/linux/build_bug.h:69:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
     BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
     ^~~~~~~~~~~~~~~~
>> mm/page_alloc.c:428:2: note: in expansion of macro 'BUILD_BUG_ON'
     BUILD_BUG_ON(order_base_2(MIGRATE_TYPES) != PB_migratetype_bits);
     ^~~~~~~~~~~~

vim +/__compiletime_assert_428 +372 include/linux/compiler.h

9a8ab1c3 Daniel Santos 2013-02-21  358  
9a8ab1c3 Daniel Santos 2013-02-21  359  #define _compiletime_assert(condition, msg, prefix, suffix) \
9a8ab1c3 Daniel Santos 2013-02-21  360  	__compiletime_assert(condition, msg, prefix, suffix)
9a8ab1c3 Daniel Santos 2013-02-21  361  
9a8ab1c3 Daniel Santos 2013-02-21  362  /**
9a8ab1c3 Daniel Santos 2013-02-21  363   * compiletime_assert - break build and emit msg if condition is false
9a8ab1c3 Daniel Santos 2013-02-21  364   * @condition: a compile-time constant condition to check
9a8ab1c3 Daniel Santos 2013-02-21  365   * @msg:       a message to emit if condition is false
9a8ab1c3 Daniel Santos 2013-02-21  366   *
9a8ab1c3 Daniel Santos 2013-02-21  367   * In tradition of POSIX assert, this macro will break the build if the
9a8ab1c3 Daniel Santos 2013-02-21  368   * supplied condition is *false*, emitting the supplied error message if the
9a8ab1c3 Daniel Santos 2013-02-21  369   * compiler has support to do so.
9a8ab1c3 Daniel Santos 2013-02-21  370   */
9a8ab1c3 Daniel Santos 2013-02-21  371  #define compiletime_assert(condition, msg) \
9a8ab1c3 Daniel Santos 2013-02-21 @372  	_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
9a8ab1c3 Daniel Santos 2013-02-21  373  

:::::: The code at line 372 was first introduced by commit
:::::: 9a8ab1c39970a4938a72d94e6fd13be88a797590 bug.h, compiler.h: introduce compiletime_assert & BUILD_BUG_ON_MSG

:::::: TO: Daniel Santos <daniel.santos@pobox.com>
:::::: CC: Linus Torvalds <torvalds@linux-foundation.org>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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Re: [PATCH] mm/pageblock: throw compiling time error if pageblock_bits can not hold MIGRATE_TYPES

[Pingfan Liu]

On Wed, Dec 5, 2018 at 4:06 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> Currently, NR_PAGEBLOCK_BITS and MIGRATE_TYPES are not associated by code.
> If someone adds extra migrate type, then he may forget to enlarge the
> NR_PAGEBLOCK_BITS.
> NR_PAGEBLOCK_BITS depends on MIGRATE_TYPES, while these macro
> spread on two different .h file with reverse dependency, it is a little
> hard to refer to MIGRATE_TYPES in pageblock-flag.h. This patch tries to
> remind such relation in compiling-time.
>
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> ---
>  include/linux/pageblock-flags.h | 5 +++--
>  mm/page_alloc.c                 | 2 +-
>  2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
> index 9132c5c..fe0aec4 100644
> --- a/include/linux/pageblock-flags.h
> +++ b/include/linux/pageblock-flags.h
> @@ -25,11 +25,12 @@
>
>  #include <linux/types.h>
>
> +#define PB_migratetype_bits 3
>  /* Bit indices that affect a whole block of pages */
>  enum pageblock_bits {
>         PB_migrate,
> -       PB_migrate_end = PB_migrate + 3 - 1,
> -                       /* 3 bits required for migrate types */
> +       PB_migrate_end = PB_migrate + PB_migratetype_bits - 1,
> +                       /* n bits required for migrate types */
>         PB_migrate_skip,/* If set the block is skipped by compaction */
>
>         /*
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2ec9cc4..537020f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -425,7 +425,7 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
>         unsigned long bitidx, word_bitidx;
>         unsigned long old_word, word;
>
> -       BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
> +       BUILD_BUG_ON(order_base_2(MIGRATE_TYPES) != PB_migratetype_bits);
>
Sorry, I made a mistake. It should be (PB_migratetype_bits -1). I will
send out V2

Regards,
Pingfan
>         bitmap = get_pageblock_bitmap(page, pfn);
>         bitidx = pfn_to_bitidx(page, pfn);
> --
> 2.7.4
>