linux-kernel - Re: [patch 3/6] mm: fix fault vs invalidate race for linear mappings

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Date:	Tue, 6 Mar 2007 23:08:41 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linux Memory Management <linux-mm@...ck.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [patch 3/6] mm: fix fault vs invalidate race for linear
 mappings

On Wed, 7 Mar 2007 07:57:27 +0100 Nick Piggin <npiggin@...e.de> wrote:

> > 
> > Why was truncate_inode_pages_range() altered to unmap the page if it got
> > mapped again?
> > 
> > Oh.  Because the unmap_mapping_range() call got removed from vmtruncate(). 
> > Why?  (Please send suitable updates to the changelog).
> 
> We have to ensure it is unmapped, and be prepared to unmap it while under
> the page lock.

But vmtruncate() dropped i_size, so nobody will map this page into
pagetables from then on.

> > I guess truncate of a mmapped area isn't sufficiently common to worry about
> > the inefficiency of this change.
> 
> Yeah, and it should be more efficient for files that aren't mmapped,
> because we don't have to take i_mmap_lock for them.
> 
> > Lots of memory barriers got removed in memory.c, unchangeloggedly.
> 
> Yeah they were all for the lockless truncate_count checks. Now that
> we use the page lock, we don't need barriers.
> 
> > Gratuitous renaming of locals in do_no_page() makes the change hard to
> > review.  Should have been a separate patch.
> > 
> > In fact, the patch would have been heaps clearer if that renaming had been
> > a separate patch.
> 
> Shall I?

If you don't have anything better to do, yes please ;)

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