Re: [f2fs-dev] [PATCH] f2fs: refactor __find_rev_next_{zero}_bit

From: Jaegeuk Kim
Date: Thu Oct 22 2015 - 12:36:32 EST

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In reply to: Chao Yu: "RE: [f2fs-dev] [PATCH] f2fs: refactor __find_rev_next_{zero}_bit"
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Hi Chao,

On Thu, Oct 22, 2015 at 07:24:01PM +0800, Chao Yu wrote:
> Hi Jaegeuk,
>
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx]
> > Sent: Thursday, October 22, 2015 6:30 AM
> > To: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx;
> > linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> > Subject: Re: [f2fs-dev] [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.
>
> Actually I didn't know the history here, could you please explain details
> about the bugs? then I can do the review.

When I disabled the existing function by:

commit e19ef527aa32f057710ec842fe656bffc263b0bb
Author: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Date: Mon May 18 11:45:15 2015 -0700

f2fs: avoid buggy functions

I found a mismatch of results between the existing __find_rev_next_bit and
f2fs_test_bit work. I remember it happened on __find_rev_next_bit sometimes
by xfstests which include trim_fs.
(I didn't get an error from __find_rev_zero_bit though.)

Since I have no time to investigate the bug in more detail at that time, I
just disabled it. But, now I'm trying to refactor the flow to fix this.

Thanks,

>
> Thanks,
>
> > >
> > > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > > ---
> > > 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
> >
> > ------------------------------------------------------------------------------
> > _______________________________________________
> > Linux-f2fs-devel mailing list
> > Linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
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Next message: kbuild test robot: "[RFC PATCH] locks: posix_lock_inode_wait() can be static"
Previous message: Bjorn Helgaas: "Re: [PATCH v11 1/6] PCI: designware: move calculation of bus addresses to DRA7xx"
In reply to: Chao Yu: "RE: [f2fs-dev] [PATCH] f2fs: refactor __find_rev_next_{zero}_bit"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]