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Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first class 
	citizen
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Wu Fengguang <fengguang.wu@intel.com>
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>> I don't think this is desirable, like Andrew already said, there's tons
>> of ways to defeat any of this and we've so far always priorized mappings
>> over !mappings. Limiting this to only PROT_EXEC mappings is already less
>> than it used to be.
>
> Yeah. One thing I realized in readahead is that *anything* can happen.
> When it comes to caching, app/user behaviors are *far more* unpredictable.
> We can make the heuristics as large as 1000LOC (and leave users and
> ourselves lost in the mist) or as simple as 100LOC (and make it happy
> to hacking or even abuse).

umm. I think it isn't good example.
Please see recent_scan/rotate stastics. it use only less 100LOC.

Plus, I don't think stastics is wrong.
if the page can claim "I'm high priority", it's risky. bad userland
program might exploit this rule.
but if the page claim "I think PROT_EXEC is important, maybe", it
isn't risky. if user-program want to exploit the rule, kernel ignore
the claim.