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

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Date:	Fri, 8 May 2009 11:30:04 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Elladan <elladan@...imo.com>, Nick Piggin <npiggin@...e.de>,
	Christoph Lameter <cl@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first
	class citizen

On Thu, May 07, 2009 at 11:17:46PM +0800, Peter Zijlstra wrote:
> On Thu, 2009-05-07 at 17:10 +0200, Johannes Weiner wrote:
> 
> > > @@ -1269,8 +1270,15 @@ static void shrink_active_list(unsigned 
> > >  
> > >  		/* page_referenced clears PageReferenced */
> > >  		if (page_mapping_inuse(page) &&
> > > -		    page_referenced(page, 0, sc->mem_cgroup))
> > > +		    page_referenced(page, 0, sc->mem_cgroup)) {
> > > +			struct address_space *mapping = page_mapping(page);
> > > +
> > >  			pgmoved++;
> > > +			if (mapping && test_bit(AS_EXEC, &mapping->flags)) {
> > > +				list_add(&page->lru, &l_active);
> > > +				continue;
> > > +			}
> > > +		}
> > 
> > Since we walk the VMAs in page_referenced anyway, wouldn't it be
> > better to check if one of them is executable?  This would even work
> > for executable anon pages.  After all, there are applications that cow
> > executable mappings (sbcl and other language environments that use an
> > executable, run-time modified core image come to mind).
> 
> Hmm, like provide a vm_flags mask along to page_referenced() to only
> account matching vmas... seems like a sensible idea.

I'd prefer to make vm_flags an out-param, like this:

-       int page_referenced(struct page *page, int is_locked,
+       int page_referenced(struct page *page, int is_locked, unsigned long *vm_flags,
                                struct mem_cgroup *mem_cont)

which allows reporting more versatile flags and status bits :) 

Thanks,
Fengguang

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