On Sat, 7 Apr 2007 18:32:04 -0700 (PDT) Christoph Lameter <[EMAIL PROTECTED]> wrote:
> On Sat, 7 Apr 2007, Andrew Morton wrote: > > > > I just tried the approach that we discussed earlier and it was not > > > nice either. > > > > We've discussed at least three approaches, so we don't know to what you > > refer. > > Thats the approach of checking two flags at the same time. In that case > the compiler will generate and "and-immediate" and then a > "compare-immediate" one branch but .... Yuck. Right. movl (%ebx), %eax # <variable>.flags, tmp399 andl $48, %eax #, tmp399 cmpl $48, %eax #, tmp399 je .L265 #, what's "yuck" about that? With the single page flag: movl (%ebx), %eax #* page.521, D.21940 testb $32, %al #, D.21940 jne .L265 #, So you're talking about saving one sole single silly solitary instruction. > > Because I don't expect there will be much efficiency difference between the > > above and the use of another page flag. > > Then we end up with all these small efficiency differences in all > the code paths. I'd rather go for optimal performance in a frequently used > construct like this. You can save that worrisome single instruction in the common case by putting the handling of the uncommon compound pages out of line, as I indicated. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/