On Fri, May 18, 2007 at 11:14:26AM -0700, Christoph Lameter wrote:
> On Fri, 18 May 2007, Nick Piggin wrote:
>
> > However we don't have to let those 8 bytes go to waste: we can use them
> > to store the virtual address of the page, which kind of makes sense for
> > 64-bit, because they can likely to use complicated memory models.
>
> That is not a valid consideration anymore. There is virtual memmap update
> pending with the sparsemem folks that will simplify things.
>
> > Many batch operations on struct page are completely random, and as such, I
> > think it is better if each struct page fits completely into a single
> > cacheline even if it means being slightly larger.
>
> Right. That would simplify the calculations.
It isn't the calculations I'm worried about, although they'll get simpler
too. It is the cache cost.
> > Don't let this space go to waste though, we can use page->virtual in order
> > to optimise page_address operations.
>
> page->virtual is a benefit if the page is cache hot. Otherwise it may
> cause a useless lookup.
It would be very rare for the page not to be in L1 cache at this point,
because we've likely taken a reference on it and/or locked it or moved it
between lists etc.
> I wonder if there are other uses for the free space?
Hugh points out that we should make _count and _mapcount atomic_long_t's,
which would probably be a better use of the space once your vmemmap goes
in.
-
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/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
