Re: scalable kmap (was Re: vm lock contention reduction)

Benjamin LaHaise
2002-07-08T21:08:41Z

On Mon, Jul 08, 2002 at 01:39:04PM -0700, Andrew Morton wrote:
> I think I'll just go for pinning the damn page. It's a spinlock and
> maybe three cachelines but the kernel is about to do a 4k memcpy
> anyway. And get_user_pages() doesn't show up much on O_DIRECT
> profiles and it'll be a net win and we need to do SOMETHING, dammit.

Pinning the page costs too much (remember, it's only a win with a
reduced copy of more that 512 bytes). The right way of doing it is
letting copy_*_user fail on a page fault for places like this where
we need to drop locks before going into the page fault handler.

-ben
--
"You will be reincarnated as a toad; and you will be much happier."