On Fri, 23 Mar 2007 07:50:28 -0700 (PDT)
Christoph Lameter <[EMAIL PROTECTED]> wrote:
> On Fri, 23 Mar 2007, Eric Dumazet wrote:
>
> > Checking Christoph quicklist implementation, I found the same cache miss in
> > free() than SLAB has.
> >
> > /* common implementation *
> > int virt_to_nid(const void *addr)
> > {
> > struct page *page = virt_to_page(addr);
> > return page_to_nid(page);
> > }
> >
> > On some platforms (x86_64 for example), could we have a better
> > implementation, not accessing struct page, but using phys_to_nid() ?
>
> This is going to pollute the caches since we then use multiple ways to
> determine the node of a page. Its better to stay with the same approach
> for all pages. The page struct is used for many other purposes as well.
> Its likely to be in the cpu cache.
>
Sorry ? page structs are not in cpu cache at all.
phys_to_nid() on my 16 GB x86_64 machine uses one single cache line, shared by
all pages.
This single cache line is cache hot yes, not "struct page"s ...
And on this machine, thats about 224 Mbytes of 'struct pages'
You carefully commented your alloc() function saying it is touching two cache
lines.
But you omited to say that free() function needs 3 cache lines if CONFIG_NUMA
For SLAB use, page struct is needed because we use lru.{next|prev} to store
slab/cachep pointers, but for a pure page allocator, unless I misread your
patch, we dont need it, if virt_to_nid() can do its job without it.
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