[PATCH v2 01/10] string: introduce memweight

[PATCH v2 01/10] string: introduce memweight

[Akinobu Mita]

memweight() is the function that counts the total number of bits set
in memory area.  Unlike bitmap_weight(), memweight() takes pointer
and size in bytes to specify a memory area which does not need to be
aligned to long-word boundary.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Anders Larsen <al@alarsen.net>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: dm-devel@redhat.com
Cc: linux-fsdevel@vger.kernel.org
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: linux-media@vger.kernel.org
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: ocfs2-devel@oss.oracle.com
Cc: Jan Kara <jack@suse.cz>
Cc: linux-ext4@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Matthew Wilcox <matthew@wil.cx>
---

v2: simplify memweight(), adviced by Jan Kara

 include/linux/string.h |    3 +++
 lib/string.c           |   32 ++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 0 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index e033564..ffe0442 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix)
 	return strncmp(str, prefix, strlen(prefix)) == 0;
 }
 #endif
+
+extern size_t memweight(const void *ptr, size_t bytes);
+
 #endif /* _LINUX_STRING_H_ */
diff --git a/lib/string.c b/lib/string.c
index e5878de..bf4d5a8 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -26,6 +26,7 @@
 #include <linux/export.h>
 #include <linux/bug.h>
 #include <linux/errno.h>
+#include <linux/bitmap.h>
 
 #ifndef __HAVE_ARCH_STRNICMP
 /**
@@ -824,3 +825,34 @@ void *memchr_inv(const void *start, int c, size_t bytes)
 	return check_bytes8(start, value, bytes % 8);
 }
 EXPORT_SYMBOL(memchr_inv);
+
+/**
+ * memweight - count the total number of bits set in memory area
+ * @ptr: pointer to the start of the area
+ * @bytes: the size of the area
+ */
+size_t memweight(const void *ptr, size_t bytes)
+{
+	size_t w = 0;
+	size_t longs;
+	const unsigned char *bitmap = ptr;
+
+	for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
+			bytes--, bitmap++)
+		w += hweight8(*bitmap);
+
+	longs = bytes / sizeof(long);
+	if (longs) {
+		BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
+		w += bitmap_weight((unsigned long *)bitmap,
+				longs * BITS_PER_LONG);
+		bytes -= longs * sizeof(long);
+		bitmap += longs * sizeof(long);
+	}
+
+	for (; bytes > 0; bytes--, bitmap++)
+		w += hweight8(*bitmap);
+
+	return w;
+}
+EXPORT_SYMBOL(memweight);
-- 
1.7.7.6

[PATCH v2 02/10] minixfs: use memweight()

[Akinobu Mita]

Use memweight() to count the total number of bits clear in memory area.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: linux-fsdevel@vger.kernel.org
---

No changes from v1

 fs/minix/bitmap.c |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/minix/bitmap.c b/fs/minix/bitmap.c
index 4bc50da..564f1a5 100644
--- a/fs/minix/bitmap.c
+++ b/fs/minix/bitmap.c
@@ -29,10 +29,8 @@ static __u32 count_free(struct buffer_head *map[], unsigned blocksize, __u32 num
 	unsigned blocks = DIV_ROUND_UP(numbits, blocksize * 8);
 
 	while (blocks--) {
-		unsigned words = blocksize / 2;
-		__u16 *p = (__u16 *)(*map++)->b_data;
-		while (words--)
-			sum += 16 - hweight16(*p++);
+		sum += blocksize * BITS_PER_BYTE -
+			memweight((*map++)->b_data, blocksize);
 	}
 
 	return sum;
-- 
1.7.7.6

Re: [PATCH v2 02/10] minixfs: use memweight()

[Jan Kara]

On Sat 02-06-12 22:40:08, Akinobu Mita wrote:
> Use memweight() to count the total number of bits clear in memory area.
> 
> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> Cc: linux-fsdevel@vger.kernel.org
> ---
> 
> No changes from v1
> 
>  fs/minix/bitmap.c |    6 ++----
>  1 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/minix/bitmap.c b/fs/minix/bitmap.c
> index 4bc50da..564f1a5 100644
> --- a/fs/minix/bitmap.c
> +++ b/fs/minix/bitmap.c
> @@ -29,10 +29,8 @@ static __u32 count_free(struct buffer_head *map[], unsigned blocksize, __u32 num
>  	unsigned blocks = DIV_ROUND_UP(numbits, blocksize * 8);
>  
>  	while (blocks--) {
> -		unsigned words = blocksize / 2;
> -		__u16 *p = (__u16 *)(*map++)->b_data;
> -		while (words--)
> -			sum += 16 - hweight16(*p++);
> +		sum += blocksize * BITS_PER_BYTE -
> +			memweight((*map++)->b_data, blocksize);
  Hmm, just using bitmap_weight() should be fine here as well AFAICS...

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

[PATCH v2 05/10] affs: use memweight()

[Akinobu Mita]

Use memweight() to count the total number of bits set in memory area.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: linux-fsdevel@vger.kernel.org
---

No changes from v1

 fs/affs/bitmap.c |   28 ++--------------------------
 1 files changed, 2 insertions(+), 26 deletions(-)

diff --git a/fs/affs/bitmap.c b/fs/affs/bitmap.c
index 3e26271..3dfdcd2 100644
--- a/fs/affs/bitmap.c
+++ b/fs/affs/bitmap.c
@@ -10,30 +10,6 @@
 #include <linux/slab.h>
 #include "affs.h"
 
-/* This is, of course, shamelessly stolen from fs/minix */
-
-static const int nibblemap[] = { 0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4 };
-
-static u32
-affs_count_free_bits(u32 blocksize, const void *data)
-{
-	const u32 *map;
-	u32 free;
-	u32 tmp;
-
-	map = data;
-	free = 0;
-	for (blocksize /= 4; blocksize > 0; blocksize--) {
-		tmp = *map++;
-		while (tmp) {
-			free += nibblemap[tmp & 0xf];
-			tmp >>= 4;
-		}
-	}
-
-	return free;
-}
-
 u32
 affs_count_free_blocks(struct super_block *sb)
 {
@@ -317,7 +293,7 @@ int affs_init_bitmap(struct super_block *sb, int *flags)
 			goto out;
 		}
 		pr_debug("AFFS: read bitmap block %d: %d\n", blk, bm->bm_key);
-		bm->bm_free = affs_count_free_bits(sb->s_blocksize - 4, bh->b_data + 4);
+		bm->bm_free = memweight(bh->b_data + 4, sb->s_blocksize - 4);
 
 		/* Don't try read the extension if this is the last block,
 		 * but we also need the right bm pointer below
@@ -367,7 +343,7 @@ int affs_init_bitmap(struct super_block *sb, int *flags)
 
 	/* recalculate bitmap count for last block */
 	bm--;
-	bm->bm_free = affs_count_free_bits(sb->s_blocksize - 4, bh->b_data + 4);
+	bm->bm_free = memweight(bh->b_data + 4, sb->s_blocksize - 4);
 
 out:
 	affs_brelse(bh);
-- 
1.7.7.6

Re: [PATCH v2 01/10] string: introduce memweight

[Jan Kara]

On Sat 02-06-12 22:40:07, Akinobu Mita wrote:
> memweight() is the function that counts the total number of bits set
> in memory area.  Unlike bitmap_weight(), memweight() takes pointer
> and size in bytes to specify a memory area which does not need to be
> aligned to long-word boundary.
> 
> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> Cc: Anders Larsen <al@alarsen.net>
> Cc: Alasdair Kergon <agk@redhat.com>
> Cc: dm-devel@redhat.com
> Cc: linux-fsdevel@vger.kernel.org
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: linux-media@vger.kernel.org
> Cc: Mark Fasheh <mfasheh@suse.com>
> Cc: Joel Becker <jlbec@evilplan.org>
> Cc: ocfs2-devel@oss.oracle.com
> Cc: Jan Kara <jack@suse.cz>
> Cc: linux-ext4@vger.kernel.org
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> Cc: "Theodore Ts'o" <tytso@mit.edu>
> Cc: Matthew Wilcox <matthew@wil.cx>
> ---
> 
> v2: simplify memweight(), adviced by Jan Kara
> 
>  include/linux/string.h |    3 +++
>  lib/string.c           |   32 ++++++++++++++++++++++++++++++++
>  2 files changed, 35 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/string.h b/include/linux/string.h
> index e033564..ffe0442 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix)
>  	return strncmp(str, prefix, strlen(prefix)) == 0;
>  }
>  #endif
> +
> +extern size_t memweight(const void *ptr, size_t bytes);
> +
>  #endif /* _LINUX_STRING_H_ */
> diff --git a/lib/string.c b/lib/string.c
> index e5878de..bf4d5a8 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -26,6 +26,7 @@
>  #include <linux/export.h>
>  #include <linux/bug.h>
>  #include <linux/errno.h>
> +#include <linux/bitmap.h>
>  
>  #ifndef __HAVE_ARCH_STRNICMP
>  /**
> @@ -824,3 +825,34 @@ void *memchr_inv(const void *start, int c, size_t bytes)
>  	return check_bytes8(start, value, bytes % 8);
>  }
>  EXPORT_SYMBOL(memchr_inv);
> +
> +/**
> + * memweight - count the total number of bits set in memory area
> + * @ptr: pointer to the start of the area
> + * @bytes: the size of the area
> + */
> +size_t memweight(const void *ptr, size_t bytes)
> +{
> +	size_t w = 0;
> +	size_t longs;
> +	const unsigned char *bitmap = ptr;
> +
> +	for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
> +			bytes--, bitmap++)
> +		w += hweight8(*bitmap);
> +
> +	longs = bytes / sizeof(long);
> +	if (longs) {
> +		BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
> +		w += bitmap_weight((unsigned long *)bitmap,
> +				longs * BITS_PER_LONG);
> +		bytes -= longs * sizeof(long);
> +		bitmap += longs * sizeof(long);
> +	}
> +
> +	for (; bytes > 0; bytes--, bitmap++)
> +		w += hweight8(*bitmap);
  Looking at bitmap_weight() it seems this last loop is not needed. Just
pass to bitmap_weight() bytes*BITS_PER_BYTE. Also generally this function
doesn't seem necessary at all at least for ext2 & ext3 (sorry for not
noticing this earlier...).

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

Re: [PATCH v2 01/10] string: introduce memweight

[Akinobu Mita]

2012/6/4 Jan Kara <jack@suse.cz>:
> On Sat 02-06-12 22:40:07, Akinobu Mita wrote:
>> memweight() is the function that counts the total number of bits set
>> in memory area.  Unlike bitmap_weight(), memweight() takes pointer
>> and size in bytes to specify a memory area which does not need to be
>> aligned to long-word boundary.
>>
>> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
>> Cc: Anders Larsen <al@alarsen.net>
>> Cc: Alasdair Kergon <agk@redhat.com>
>> Cc: dm-devel@redhat.com
>> Cc: linux-fsdevel@vger.kernel.org
>> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>> Cc: linux-media@vger.kernel.org
>> Cc: Mark Fasheh <mfasheh@suse.com>
>> Cc: Joel Becker <jlbec@evilplan.org>
>> Cc: ocfs2-devel@oss.oracle.com
>> Cc: Jan Kara <jack@suse.cz>
>> Cc: linux-ext4@vger.kernel.org
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
>> Cc: "Theodore Ts'o" <tytso@mit.edu>
>> Cc: Matthew Wilcox <matthew@wil.cx>
>> ---
>>
>> v2: simplify memweight(), adviced by Jan Kara
>>
>>  include/linux/string.h |    3 +++
>>  lib/string.c           |   32 ++++++++++++++++++++++++++++++++
>>  2 files changed, 35 insertions(+), 0 deletions(-)
>>
>> diff --git a/include/linux/string.h b/include/linux/string.h
>> index e033564..ffe0442 100644
>> --- a/include/linux/string.h
>> +++ b/include/linux/string.h
>> @@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix)
>>       return strncmp(str, prefix, strlen(prefix)) == 0;
>>  }
>>  #endif
>> +
>> +extern size_t memweight(const void *ptr, size_t bytes);
>> +
>>  #endif /* _LINUX_STRING_H_ */
>> diff --git a/lib/string.c b/lib/string.c
>> index e5878de..bf4d5a8 100644
>> --- a/lib/string.c
>> +++ b/lib/string.c
>> @@ -26,6 +26,7 @@
>>  #include <linux/export.h>
>>  #include <linux/bug.h>
>>  #include <linux/errno.h>
>> +#include <linux/bitmap.h>
>>
>>  #ifndef __HAVE_ARCH_STRNICMP
>>  /**
>> @@ -824,3 +825,34 @@ void *memchr_inv(const void *start, int c, size_t bytes)
>>       return check_bytes8(start, value, bytes % 8);
>>  }
>>  EXPORT_SYMBOL(memchr_inv);
>> +
>> +/**
>> + * memweight - count the total number of bits set in memory area
>> + * @ptr: pointer to the start of the area
>> + * @bytes: the size of the area
>> + */
>> +size_t memweight(const void *ptr, size_t bytes)
>> +{
>> +     size_t w = 0;
>> +     size_t longs;
>> +     const unsigned char *bitmap = ptr;
>> +
>> +     for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
>> +                     bytes--, bitmap++)
>> +             w += hweight8(*bitmap);
>> +
>> +     longs = bytes / sizeof(long);
>> +     if (longs) {
>> +             BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
>> +             w += bitmap_weight((unsigned long *)bitmap,
>> +                             longs * BITS_PER_LONG);
>> +             bytes -= longs * sizeof(long);
>> +             bitmap += longs * sizeof(long);
>> +     }
>> +
>> +     for (; bytes > 0; bytes--, bitmap++)
>> +             w += hweight8(*bitmap);
>  Looking at bitmap_weight() it seems this last loop is not needed. Just
> pass to bitmap_weight() bytes*BITS_PER_BYTE. Also generally this function
> doesn't seem necessary at all at least for ext2 & ext3 (sorry for not
> noticing this earlier...).

This last loop is necessary for big-endian architecture.
if bytes % sizeof(long) != 0, bitmap_weight() counts one-bits in wrong
byte-field
of the last long word.
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Re: [PATCH v2 01/10] string: introduce memweight

[Jan Kara]

On Mon 04-06-12 20:46:14, Akinobu Mita wrote:
> 2012/6/4 Jan Kara <jack@suse.cz>:
> > On Sat 02-06-12 22:40:07, Akinobu Mita wrote:
> >> memweight() is the function that counts the total number of bits set
> >> in memory area.  Unlike bitmap_weight(), memweight() takes pointer
> >> and size in bytes to specify a memory area which does not need to be
> >> aligned to long-word boundary.
> >>
> >> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> >> Cc: Anders Larsen <al@alarsen.net>
> >> Cc: Alasdair Kergon <agk@redhat.com>
> >> Cc: dm-devel@redhat.com
> >> Cc: linux-fsdevel@vger.kernel.org
> >> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> >> Cc: linux-media@vger.kernel.org
> >> Cc: Mark Fasheh <mfasheh@suse.com>
> >> Cc: Joel Becker <jlbec@evilplan.org>
> >> Cc: ocfs2-devel@oss.oracle.com
> >> Cc: Jan Kara <jack@suse.cz>
> >> Cc: linux-ext4@vger.kernel.org
> >> Cc: Andrew Morton <akpm@linux-foundation.org>
> >> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> >> Cc: "Theodore Ts'o" <tytso@mit.edu>
> >> Cc: Matthew Wilcox <matthew@wil.cx>
> >> ---
> >>
> >> v2: simplify memweight(), adviced by Jan Kara
> >>
> >>  include/linux/string.h |    3 +++
> >>  lib/string.c           |   32 ++++++++++++++++++++++++++++++++
> >>  2 files changed, 35 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/include/linux/string.h b/include/linux/string.h
> >> index e033564..ffe0442 100644
> >> --- a/include/linux/string.h
> >> +++ b/include/linux/string.h
> >> @@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix)
> >>       return strncmp(str, prefix, strlen(prefix)) == 0;
> >>  }
> >>  #endif
> >> +
> >> +extern size_t memweight(const void *ptr, size_t bytes);
> >> +
> >>  #endif /* _LINUX_STRING_H_ */
> >> diff --git a/lib/string.c b/lib/string.c
> >> index e5878de..bf4d5a8 100644
> >> --- a/lib/string.c
> >> +++ b/lib/string.c
> >> @@ -26,6 +26,7 @@
> >>  #include <linux/export.h>
> >>  #include <linux/bug.h>
> >>  #include <linux/errno.h>
> >> +#include <linux/bitmap.h>
> >>
> >>  #ifndef __HAVE_ARCH_STRNICMP
> >>  /**
> >> @@ -824,3 +825,34 @@ void *memchr_inv(const void *start, int c, size_t bytes)
> >>       return check_bytes8(start, value, bytes % 8);
> >>  }
> >>  EXPORT_SYMBOL(memchr_inv);
> >> +
> >> +/**
> >> + * memweight - count the total number of bits set in memory area
> >> + * @ptr: pointer to the start of the area
> >> + * @bytes: the size of the area
> >> + */
> >> +size_t memweight(const void *ptr, size_t bytes)
> >> +{
> >> +     size_t w = 0;
> >> +     size_t longs;
> >> +     const unsigned char *bitmap = ptr;
> >> +
> >> +     for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
> >> +                     bytes--, bitmap++)
> >> +             w += hweight8(*bitmap);
> >> +
> >> +     longs = bytes / sizeof(long);
> >> +     if (longs) {
> >> +             BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
> >> +             w += bitmap_weight((unsigned long *)bitmap,
> >> +                             longs * BITS_PER_LONG);
> >> +             bytes -= longs * sizeof(long);
> >> +             bitmap += longs * sizeof(long);
> >> +     }
> >> +
> >> +     for (; bytes > 0; bytes--, bitmap++)
> >> +             w += hweight8(*bitmap);
> >  Looking at bitmap_weight() it seems this last loop is not needed. Just
> > pass to bitmap_weight() bytes*BITS_PER_BYTE. Also generally this function
> > doesn't seem necessary at all at least for ext2 & ext3 (sorry for not
> > noticing this earlier...).
> 
> This last loop is necessary for big-endian architecture.
> if bytes % sizeof(long) != 0, bitmap_weight() counts one-bits in wrong
> byte-field
> of the last long word.
  Ah, right. OK. Add this to the comment before the loop please. You save
yourself some explanations :)

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR
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Re: [PATCH v2 01/10] string: introduce memweight

[Akinobu Mita]

2012/6/4 Jan Kara <jack@suse.cz>:
> On Mon 04-06-12 20:46:14, Akinobu Mita wrote:
>> 2012/6/4 Jan Kara <jack@suse.cz>:
>> > On Sat 02-06-12 22:40:07, Akinobu Mita wrote:
>> >> memweight() is the function that counts the total number of bits set
>> >> in memory area. áUnlike bitmap_weight(), memweight() takes pointer
>> >> and size in bytes to specify a memory area which does not need to be
>> >> aligned to long-word boundary.
>> >>
>> >> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
>> >> Cc: Anders Larsen <al@alarsen.net>
>> >> Cc: Alasdair Kergon <agk@redhat.com>
>> >> Cc: dm-devel@redhat.com
>> >> Cc: linux-fsdevel@vger.kernel.org
>> >> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>> >> Cc: linux-media@vger.kernel.org
>> >> Cc: Mark Fasheh <mfasheh@suse.com>
>> >> Cc: Joel Becker <jlbec@evilplan.org>
>> >> Cc: ocfs2-devel@oss.oracle.com
>> >> Cc: Jan Kara <jack@suse.cz>
>> >> Cc: linux-ext4@vger.kernel.org
>> >> Cc: Andrew Morton <akpm@linux-foundation.org>
>> >> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
>> >> Cc: "Theodore Ts'o" <tytso@mit.edu>
>> >> Cc: Matthew Wilcox <matthew@wil.cx>
>> >> ---
>> >>
>> >> v2: simplify memweight(), adviced by Jan Kara
>> >>
>> >> áinclude/linux/string.h | á á3 +++
>> >> álib/string.c á á á á á | á 32 ++++++++++++++++++++++++++++++++
>> >> á2 files changed, 35 insertions(+), 0 deletions(-)
>> >>
>> >> diff --git a/include/linux/string.h b/include/linux/string.h
>> >> index e033564..ffe0442 100644
>> >> --- a/include/linux/string.h
>> >> +++ b/include/linux/string.h
>> >> @@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix)
>> >> á á á return strncmp(str, prefix, strlen(prefix)) == 0;
>> >> á}
>> >> á#endif
>> >> +
>> >> +extern size_t memweight(const void *ptr, size_t bytes);
>> >> +
>> >> á#endif /* _LINUX_STRING_H_ */
>> >> diff --git a/lib/string.c b/lib/string.c
>> >> index e5878de..bf4d5a8 100644
>> >> --- a/lib/string.c
>> >> +++ b/lib/string.c
>> >> @@ -26,6 +26,7 @@
>> >> á#include <linux/export.h>
>> >> á#include <linux/bug.h>
>> >> á#include <linux/errno.h>
>> >> +#include <linux/bitmap.h>
>> >>
>> >> á#ifndef __HAVE_ARCH_STRNICMP
>> >> á/**
>> >> @@ -824,3 +825,34 @@ void *memchr_inv(const void *start, int c, size_t bytes)
>> >> á á á return check_bytes8(start, value, bytes % 8);
>> >> á}
>> >> áEXPORT_SYMBOL(memchr_inv);
>> >> +
>> >> +/**
>> >> + * memweight - count the total number of bits set in memory area
>> >> + * @ptr: pointer to the start of the area
>> >> + * @bytes: the size of the area
>> >> + */
>> >> +size_t memweight(const void *ptr, size_t bytes)
>> >> +{
>> >> + á á size_t w = 0;
>> >> + á á size_t longs;
>> >> + á á const unsigned char *bitmap = ptr;
>> >> +
>> >> + á á for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
>> >> + á á á á á á á á á á bytes--, bitmap++)
>> >> + á á á á á á w += hweight8(*bitmap);
>> >> +
>> >> + á á longs = bytes / sizeof(long);
>> >> + á á if (longs) {
>> >> + á á á á á á BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
>> >> + á á á á á á w += bitmap_weight((unsigned long *)bitmap,
>> >> + á á á á á á á á á á á á á á longs * BITS_PER_LONG);
>> >> + á á á á á á bytes -= longs * sizeof(long);
>> >> + á á á á á á bitmap += longs * sizeof(long);
>> >> + á á }
>> >> +
>> >> + á á for (; bytes > 0; bytes--, bitmap++)
>> >> + á á á á á á w += hweight8(*bitmap);
>> > áLooking at bitmap_weight() it seems this last loop is not needed. Just
>> > pass to bitmap_weight() bytes*BITS_PER_BYTE. Also generally this function
>> > doesn't seem necessary at all at least for ext2 & ext3 (sorry for not
>> > noticing this earlier...).
>>
>> This last loop is necessary for big-endian architecture.
>> if bytes % sizeof(long) != 0, bitmap_weight() counts one-bits in wrong
>> byte-field
>> of the last long word.
>  Ah, right. OK. Add this to the comment before the loop please. You save
> yourself some explanations :)

OK.  Thanks for your advice again.