linux-kernel - Re: [PATCH -mm] vmscan: make mapped executable pages the first class citizen

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Date:	Sat,  9 May 2009 19:20:09 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com, Elladan <elladan@...imo.com>,
	Rik van Riel <riel@...hat.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Nick Piggin <npiggin@...e.de>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first class citizen

> On Thu, 7 May 2009, Elladan wrote:
> 
> > > Nobody (except you) is proposing that we completely disable
> > > the eviction of executable pages.  I believe that your idea
> > > could easily lead to a denial of service attack, with a user
> > > creating a very large executable file and mmaping it.
> 
> The amount of mlockable pages is limited via ulimit. We can already make
> the pages unreclaimable through mlock().
> 
> > I don't know of any distro that applies default ulimits, so desktops are
> > already susceptible to the far more trivial "call malloc a lot" or "fork bomb"
> > attacks.  Plus, ulimits don't help, since they only apply per process - you'd
> > need a default mem cgroup before this mattered, I think.
> 
> The point remains that the proposed patch does not solve the general
> problem that we encounter with exec pages of critical components of the
> user interface being evicted from memory.
> 
> Do we have test data that shows a benefit? The description is minimal. Rik
> claimed on IRC that tests have been done. If so then the patch description
> should include the tests. Which loads benefit from this patch?
> 
> A significant change to the reclaim algorithm also needs to
> have a clear description of the effects on reclaim behavior which is also
> lacking.

btw,

This is very good news to me.
Recently I've taked sevaral time for reproducing this issue. but
I have no luck. I'm interesting its test-case.

Thanks.


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