From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 476486B008A for ; Sun, 10 May 2009 06:06:30 -0400 (EDT) Received: by yx-out-1718.google.com with SMTP id 36so1194214yxh.26 for ; Sun, 10 May 2009 03:06:35 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20090510093541.GB7651@localhost> References: <20090503031539.GC5702@localhost> <20090507121101.GB20934@localhost> <20090507151039.GA2413@cmpxchg.org> <20090507134410.0618b308.akpm@linux-foundation.org> <20090508081608.GA25117@localhost> <20090508125859.210a2a25.akpm@linux-foundation.org> <20090508230045.5346bd32@lxorguk.ukuu.org.uk> <2f11576a0905100159m32c36a9ep9fb7cc5604c60b2@mail.gmail.com> <1241946446.6317.42.camel@laptop> <20090510093541.GB7651@localhost> Date: Sun, 10 May 2009 19:06:34 +0900 Message-ID: <2f11576a0905100306q3c087da8td834026a5161fe68@mail.gmail.com> Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first class citizen From: KOSAKI Motohiro Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: Peter Zijlstra , Alan Cox , Andrew Morton , "hannes@cmpxchg.org" , "riel@redhat.com" , "linux-kernel@vger.kernel.org" , "tytso@mit.edu" , "linux-mm@kvack.org" , "elladan@eskimo.com" , "npiggin@suse.de" , "cl@linux-foundation.org" , "minchan.kim@gmail.com" List-ID: >> 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org