To: a.p.zijlstra@chello.nl
CC: salikhmetov@gmail.com, linux-mm@kvack.org, jakob@unthought.net,
       linux-kernel@vger.kernel.org, valdis.kletnieks@vt.edu, riel@redhat.com,
       ksm@42.dk, staubach@redhat.com, jesper.juhl@gmail.com,
       torvalds@linux-foundation.org, akpm@linux-foundation.org,
       protasnb@gmail.com, miklos@szeredi.hu, r.e.wolff@bitwizard.nl,
       hidave.darkstar@gmail.com, hch@infradead.org
In-reply-to: <1201078278.6341.47.camel@lappy> (message from Peter Zijlstra on
	Wed, 23 Jan 2008 09:51:18 +0100)
Subject: Re: [PATCH -v8 3/4] Enable the MS_ASYNC functionality in
	sys_msync()
References: <12010440803930-git-send-email-salikhmetov@gmail.com>
	 <1201044083504-git-send-email-salikhmetov@gmail.com>
	 <1201078035.6341.45.camel@lappy> <1201078278.6341.47.camel@lappy>
Message-Id: <E1JHc0S-00027S-8D@pomaz-ex.szeredi.hu>
From: Miklos Szeredi <miklos@szeredi.hu>
Date: Wed, 23 Jan 2008 10:34:52 +0100
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1456
Lines: 41

> On Wed, 2008-01-23 at 09:47 +0100, Peter Zijlstra wrote:
> > On Wed, 2008-01-23 at 02:21 +0300, Anton Salikhmetov wrote:
> 
> > > +static void vma_wrprotect(struct vm_area_struct *vma)
> > > +{
> > > +	unsigned long addr = vma->vm_start;
> > > +	pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
> > > +
> > > +	while (addr < vma->vm_end) {
> > > +		unsigned long next = pgd_addr_end(addr, vma->vm_end);
> > > +
> > > +		if (!pgd_none_or_clear_bad(pgd))
> > > +			vma_wrprotect_pgd_range(vma, pgd, addr, next);
> > > +
> > > +		++pgd;
> > > +		addr = next;
> > > +	}
> > > +}
> > 
> > I think you want to pass start, end here too, you might not need to
> > sweep the whole vma.
> 
> Also, it still doesn't make sense to me why we'd not need to walk the
> rmap, it is all the same file after all.

It's the same file, but not the same memory map.  It basically depends
on how you define msync:

 a) sync _file_ on region defined by this mmap/start/end-address
 b) sync _memory_region_ defined by start/end-address

b) is a perfectly fine definition, and it's consistent with what this
code does.  The fact that POSIX probably implies a) (in a rather
poorly defined way) doesn't make much difference, I think.

Miklos
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