On Thu, 6 Nov 2014, Dave Hansen wrote:

Instead of all of these games with dropping and reacquiring mmap_sem and
adding other locks, or deferring the work, why don't we just do a
get_user_pages()?  Something along the lines of:

while (1) {
	ret = cmpxchg(addr)
	if (!ret)
		break;
	if (ret == -EFAULT)
		get_user_pages(addr);
}

Does anybody see a problem with that?

You want to do that under mmap_sem write held, right? Not a problem per
se, except that you block normal faults for a possibly long time when
the page(s) need to be swapped in.

But yes, this might solve most of the issues at hand. Did not think
about GUP at all :(

Thanks,

	tglx