On Mon, Jan 01, 2007 at 03:01:52PM -0800, David Miller wrote: > From: James Bottomley <[EMAIL PROTECTED]> > Date: Mon, 01 Jan 2007 10:34:12 -0600 > > > Erm, well the whole reason for the flush_anon_pages() was that you told > > me not to do it in flush_dcache_page() ... > > > > Although this is perhaps part of the confusion over what > > flush_dcache_page() is actually supposed to do. > > I completely agree, it's confusing. I've tried to make it > "just a hook" where architectures do whatever is necessary > at that point to synchronize things. It's a poor definition > and gives the implementor not much more than a rope with which > to hang themselves :-) > > That's why I'm thinking strongly about perhaps encouraging > people to go the kmap() route. It would avoid all the flushing > in exchange for some specialized TLB accesses. If the flushes > are really expensive, and the TLB operations to setup/teardown > the kmap()'s can be relatively cheap, it might be the thing to > do on PARISC.
This all sounds wonderful, and also means that if/when ARM starts implementing highmem, kmap becomes useful. (When I looked at that a while back, adding the necessary flushes where required would mean that we ended up doing a lot of flushing all over the place.) > More and more I like Ralf's kmap() approach because you only > do things exactly where the kernel actually touches the page. > And if it would really help in some way, we can even tag the > kmap() calls with "KMAP_READ" or "KMAP_WRITE" type attributes > as appropriate. Because let's say you don't want to do the > TLB mapping thing, and still want to actually cache flush, > then this hint about the access could guide what kind of flush > you do. You'd still want to do the flushing on ARM because it's mostly VIVT. Remapping pages with VIVT would just makes things much worse. So yes, this sounds like a great idea. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: - To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
