Re: [v3 0/9] parallelized "struct page" zeroing

Matthew Wilcox
2017-05-10T21:11:31Z

On Wed, May 10, 2017 at 02:00:26PM -0400, David Miller wrote:
> From: Matthew Wilcox <willy@infradead.org>
> Date: Wed, 10 May 2017 10:17:03 -0700
> > On Wed, May 10, 2017 at 11:19:43AM -0400, David Miller wrote:
> >> I guess it might be clearer if you understand what the block
> >> initializing stores do on sparc64. There are no memory accesses at
> >> all.
> >>
> >> The cpu just zeros out the cache line, that's it.
> >>
> >> No L3 cache line is allocated. So this "wipe everything" behavior
> >> will not happen in the L3.
> >
> > There's either something wrong with your explanation or my reading
> > skills :-)
> >
> > "There are no memory accesses"
> > "No L3 cache line is allocated"
> >
> > You can have one or the other ... either the CPU sends a cacheline-sized
> > write of zeroes to memory without allocating an L3 cache line (maybe
> > using the store buffer?), or the CPU allocates an L3 cache line and sets
> > its contents to zeroes, probably putting it in the last way of the set
> > so it's the first thing to be evicted if not touched.
>
> There is no conflict in what I said.
>
> Only an L2 cache line is allocated and cleared. L3 is left alone.

I thought SPARC had inclusive caches. So allocating an L2 cacheline
would necessitate allocating an L3 cacheline. Or is this an exception
to the normal order of things?