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Date: Wed, 21 Oct 2015 15:29:33 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH] f2fs: refactor __find_rev_next_{zero}_bit
On Wed, Oct 21, 2015 at 02:16:43PM -0700, Jaegeuk Kim wrote:
> This patch refactors __find_rev_next_{zero}_bit which was disabled previously
> due to bugs.
>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
> fs/f2fs/segment.c | 106 +++++++++++++++++++++++++-----------------------------
> 1 file changed, 49 insertions(+), 57 deletions(-)
>
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index f37c212..50afc93 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -29,6 +29,21 @@ static struct kmem_cache *discard_entry_slab;
> static struct kmem_cache *sit_entry_set_slab;
> static struct kmem_cache *inmem_entry_slab;
>
> +static unsigned long __reverse_ulong(unsigned char *str)
> +{
> + unsigned long tmp = 0;
> + int shift = 24, idx = 0;
> +
> +#if BITS_PER_LONG == 64
> + shift = 56;
> +#endif
> + while (shift >= 0) {
> + tmp |= (unsigned long)str[idx++] << shift;
> + shift -= BITS_PER_BYTE;
> + }
> + return tmp;
> +}
> +
> /*
> * __reverse_ffs is copied from include/asm-generic/bitops/__ffs.h since
> * MSB and LSB are reversed in a byte by f2fs_set_bit.
> @@ -38,27 +53,31 @@ static inline unsigned long __reverse_ffs(unsigned long word)
> int num = 0;
>
> #if BITS_PER_LONG == 64
> - if ((word & 0xffffffff) == 0) {
> + if ((word & 0xffffffff00000000) == 0)
I fixed the sparse warning by modifying:
if ((word & 0xffffffff00000000UL) == 0)
Thanks,
> num += 32;
> + else
> word >>= 32;
> - }
> #endif
> - if ((word & 0xffff) == 0) {
> + if ((word & 0xffff0000) == 0)
> num += 16;
> + else
> word >>= 16;
> - }
> - if ((word & 0xff) == 0) {
> +
> + if ((word & 0xff00) == 0)
> num += 8;
> + else
> word >>= 8;
> - }
> +
> if ((word & 0xf0) == 0)
> num += 4;
> else
> word >>= 4;
> +
> if ((word & 0xc) == 0)
> num += 2;
> else
> word >>= 2;
> +
> if ((word & 0x2) == 0)
> num += 1;
> return num;
> @@ -68,26 +87,16 @@ static inline unsigned long __reverse_ffs(unsigned long word)
> * __find_rev_next(_zero)_bit is copied from lib/find_next_bit.c because
> * f2fs_set_bit makes MSB and LSB reversed in a byte.
> * Example:
> - * LSB <--> MSB
> - * f2fs_set_bit(0, bitmap) => 0000 0001
> - * f2fs_set_bit(7, bitmap) => 1000 0000
> + * MSB <--> LSB
> + * f2fs_set_bit(0, bitmap) => 1000 0000
> + * f2fs_set_bit(7, bitmap) => 0000 0001
> */
> static unsigned long __find_rev_next_bit(const unsigned long *addr,
> unsigned long size, unsigned long offset)
> {
> - while (!f2fs_test_bit(offset, (unsigned char *)addr))
> - offset++;
> -
> - if (offset > size)
> - offset = size;
> -
> - return offset;
> -#if 0
> const unsigned long *p = addr + BIT_WORD(offset);
> unsigned long result = offset & ~(BITS_PER_LONG - 1);
> unsigned long tmp;
> - unsigned long mask, submask;
> - unsigned long quot, rest;
>
> if (offset >= size)
> return size;
> @@ -97,14 +106,9 @@ static unsigned long __find_rev_next_bit(const unsigned long *addr,
> if (!offset)
> goto aligned;
>
> - tmp = *(p++);
> - quot = (offset >> 3) << 3;
> - rest = offset & 0x7;
> - mask = ~0UL << quot;
> - submask = (unsigned char)(0xff << rest) >> rest;
> - submask <<= quot;
> - mask &= submask;
> - tmp &= mask;
> + tmp = __reverse_ulong((unsigned char *)p);
> + tmp &= ~0UL >> offset;
> +
> if (size < BITS_PER_LONG)
> goto found_first;
> if (tmp)
> @@ -112,42 +116,34 @@ static unsigned long __find_rev_next_bit(const unsigned long *addr,
>
> size -= BITS_PER_LONG;
> result += BITS_PER_LONG;
> + p++;
> aligned:
> while (size & ~(BITS_PER_LONG-1)) {
> - tmp = *(p++);
> + tmp = __reverse_ulong((unsigned char *)p);
> if (tmp)
> goto found_middle;
> result += BITS_PER_LONG;
> size -= BITS_PER_LONG;
> + p++;
> }
> if (!size)
> return result;
> - tmp = *p;
> +
> + tmp = __reverse_ulong((unsigned char *)p);
> found_first:
> - tmp &= (~0UL >> (BITS_PER_LONG - size));
> - if (tmp == 0UL) /* Are any bits set? */
> + tmp &= (~0UL << (BITS_PER_LONG - size));
> + if (!tmp) /* Are any bits set? */
> return result + size; /* Nope. */
> found_middle:
> return result + __reverse_ffs(tmp);
> -#endif
> }
>
> static unsigned long __find_rev_next_zero_bit(const unsigned long *addr,
> unsigned long size, unsigned long offset)
> {
> - while (f2fs_test_bit(offset, (unsigned char *)addr))
> - offset++;
> -
> - if (offset > size)
> - offset = size;
> -
> - return offset;
> -#if 0
> const unsigned long *p = addr + BIT_WORD(offset);
> unsigned long result = offset & ~(BITS_PER_LONG - 1);
> unsigned long tmp;
> - unsigned long mask, submask;
> - unsigned long quot, rest;
>
> if (offset >= size)
> return size;
> @@ -157,40 +153,36 @@ static unsigned long __find_rev_next_zero_bit(const unsigned long *addr,
> if (!offset)
> goto aligned;
>
> - tmp = *(p++);
> - quot = (offset >> 3) << 3;
> - rest = offset & 0x7;
> - mask = ~(~0UL << quot);
> - submask = (unsigned char)~((unsigned char)(0xff << rest) >> rest);
> - submask <<= quot;
> - mask += submask;
> - tmp |= mask;
> + tmp = __reverse_ulong((unsigned char *)p);
> + tmp |= ~((~0UL << offset) >> offset);
> +
> if (size < BITS_PER_LONG)
> goto found_first;
> - if (~tmp)
> + if (tmp != ~0UL)
> goto found_middle;
>
> size -= BITS_PER_LONG;
> result += BITS_PER_LONG;
> + p++;
> aligned:
> while (size & ~(BITS_PER_LONG - 1)) {
> - tmp = *(p++);
> - if (~tmp)
> + tmp = __reverse_ulong((unsigned char *)p);
> + if (tmp != ~0UL)
> goto found_middle;
> result += BITS_PER_LONG;
> size -= BITS_PER_LONG;
> + p++;
> }
> if (!size)
> return result;
> - tmp = *p;
>
> + tmp = __reverse_ulong((unsigned char *)p);
> found_first:
> - tmp |= ~0UL << size;
> - if (tmp == ~0UL) /* Are any bits zero? */
> + tmp |= ~(~0UL << (BITS_PER_LONG - size));
> + if (tmp == ~0UL) /* Are any bits zero? */
> return result + size; /* Nope. */
> found_middle:
> return result + __reverse_ffz(tmp);
> -#endif
> }
>
> void register_inmem_page(struct inode *inode, struct page *page)
> --
> 2.1.1
--
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