Nick Piggin <[email protected]> wrote:
> I'd like to be the first to propose an increase to the size of struct page
> just for the sake of increasing it!
Heh. I'm surprised you haven't got more adverse reactions.
> If we add 8 bytes to struct page on 64-bit machines, it becomes 64 bytes,
> which is quite a nice number for cache purposes.
Whilst that's true, if you have to deal with a run of contiguous page structs
(eg: the page allocator, perhaps) it's actually less efficient because it
takes more cache to do it. But, hey, it's a compromise whatever.
In the scheme of things, if we're mostly dealing with individual page structs
(as I think we are), then yes, I think it's probably a good thing to do -
especially with larger page sizes.
> 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's a good idea, one that's implemented on some platforms anyway. It'll be
especially good with NUMA, I suspect.
> I'd say all up this is going to decrease overall cache footprint in
> fastpaths, both by reducing text and data footprint of page_address and
> related operations, and by reducing cacheline footprint of most batched
> operations on struct pages.
kmap, filling in scatter/gather lists, crypto stuff. I like it.
Can you do this just by turning on WANT_PAGE_VIRTUAL on all 64-bit platforms?
David
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