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

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Message-Id: <20090507134410.0618b308.akpm@linux-foundation.org>
Date:	Thu, 7 May 2009 13:44:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	fengguang.wu@...el.com, peterz@...radead.org, riel@...hat.com,
	linux-kernel@...r.kernel.org, tytso@....edu, linux-mm@...ck.org,
	elladan@...imo.com, npiggin@...e.de, cl@...ux-foundation.org,
	kosaki.motohiro@...fujitsu.com
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first
 class citizen

On Thu, 7 May 2009 17:10:39 +0200
Johannes Weiner <hannes@...xchg.org> wrote:

> > +++ linux/mm/nommu.c
> > @@ -1224,6 +1224,8 @@ unsigned long do_mmap_pgoff(struct file 
> >  			added_exe_file_vma(current->mm);
> >  			vma->vm_mm = current->mm;
> >  		}
> > +		if (vm_flags & VM_EXEC)
> > +			set_bit(AS_EXEC, &file->f_mapping->flags);
> >  	}
> 
> I find it a bit ugly that it applies an attribute of the memory area
> (per mm) to the page cache mapping (shared).  Because this in turn
> means that the reference through a non-executable vma might get the
> pages rotated just because there is/was an executable mmap around.

Yes, it's not good.  That AS_EXEC bit will hang around for arbitrarily
long periods in the inode cache.  So we'll have AS_EXEC set on an
entire file because someone mapped some of it with PROT_EXEC half an
hour ago.  Where's the sense in that?


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