Messages in this thread | | | From | David Howells <> | Subject | Re: [rfc] increase struct page size?! | Date | Fri, 18 May 2007 10:42:30 +0100 |
| |
Nick Piggin <npiggin@suse.de> 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |