linux-kernel - Re: [patch 2/2] only allow nonlinear vmas for ram backed filesystems

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Message-Id: <E1HZORc-0000UZ-00@dorka.pomaz.szeredi.hu>
Date:	Thu, 05 Apr 2007 11:39:52 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	a.p.zijlstra@...llo.nl
CC:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 2/2] only allow nonlinear vmas for ram backed
	filesystems

> > +		/*
> > +		 * page_mkclean doesn't work on nonlinear vmas, so if dirty
> > +		 * pages need to be accounted, emulate with linear vmas.
> > +		 */
> > +		if (mapping_cap_account_dirty(mapping)) {
> 
> Perhaps this should read:
> 
> 		if (vma_wants_writenotify(vma)) {
> 

I looked at that, but IIRC vma_wants_writenotify() doesn't work after
mmap(), because of the updated protection bits.

> That way we would even allow read only non-linear mappings of 'real'
> filesystem files.

Well, we could do that, but is it really worth the hassle?  The real
question is whether anyone would want to use non-linear
shared-read-only mappings or not.

Thanks,
Miklos
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