Le mardi 09 août 2011 à 18:38 +0900, Akinobu Mita a écrit :
> 2011/8/9 Eric Dumazet <eric.dumazet@xxxxxxxxx>:
>
> >> > diff --git a/mm/slub.c b/mm/slub.c
> >> > index eb5a8f9..5695f92 100644
> >> > --- a/mm/slub.c
> >> > +++ b/mm/slub.c
> >> > @@ -701,7 +701,7 @@ static u8 *check_bytes(u8 *start, u8 value, unsigned int bytes)
> >> > return check_bytes8(start, value, bytes);
> >> >
> >> > value64 = value | value << 8 | value << 16 | value << 24;
> >> > - value64 = value64 | value64 << 32;
> >> > + value64 = (value64 & 0xffffffff) | value64 << 32;
> >> > prefix = 8 - ((unsigned long)start) % 8;
> >> >
> >> > if (prefix) {
> >>
> >> Still buggy I am afraid. Could we use the following ?
> >>
> >>
> >> value64 = value;
> >> value64 |= value64 << 8;
> >> value64 |= value64 << 16;
> >> value64 |= value64 << 32;
> >>
> >>
> >
> > Well, 'buggy' was not well chosen.
> >
> > Another possibility would be to use a multiply if arch has a fast
> > multiplier...
> >
> >
> > value64 = value;
> > #if defined(ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
> > value64 *= 0x0101010101010101;
> > #elif defined(ARCH_HAS_FAST_MULTIPLIER)
> > value64 *= 0x01010101;
> > value64 |= value64 << 32;
> > #else
> > value64 |= value64 << 8;
> > value64 |= value64 << 16;
> > value64 |= value64 << 32;
> > #endif
>
> I don't really care about which one should be used. So tell me if I need
> to resend it with this improvement.
It would be nice to fix all bugs while we review this code.
Lets push your patch and I'll submit a patch for next kernel.
For example, following code is suboptimal :
prefix = 8 - ((unsigned long)start) % 8;
if (prefix) {
u8 *r = check_bytes8(start, value, prefix);
if (r)
return r;
start += prefix;
bytes -= prefix;
}
Since we always have prefix = 8 if 'start' is longword aligned, so we
call check_bytes8() at least once with 8 bytes to compare...
Also, 32bit arches should be taken into account properly.
Oh well...
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