Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW

On 09/14/2018 01:39 PM, Yu-cheng Yu wrote:

With the updated ptep_set_wrprotect() below, I did MADV_WILLNEED to a shadow
stack of 8 MB, then 10,000 fork()'s, but could not prove it is more or less
efficient than the other.  So can we say this is probably fine in terms of
efficiency?

Well, the first fork() will do all the hard work.  I don't think
subsequent fork()s will be affected.

Did you do something to ensure this code was being run?

I would guess that a loop like this:

	for (i = 0; i < 10000; i++) {
		mprotect(addr, len, PROT_READ);
		mprotect(addr, len, PROT_READ|PROT_WRITE);
	}

might show it better.