linux-kernel - Re: [PATCH v2 2/3] mm: Update file times when inodes are written after mmaped writes

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Date:	Thu, 3 Jan 2013 19:56:42 +0100
From:	Jan Kara <jack@...e.cz>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Dave Chinner <david@...morbit.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2 2/3] mm: Update file times when inodes are written
 after mmaped writes

On Thu 03-01-13 09:49:37, Andy Lutomirski wrote:
> On Mon, Dec 31, 2012 at 8:11 AM, Jan Kara <jack@...e.cz> wrote:
> > On Sat 22-12-12 00:43:30, Andy Lutomirski wrote:
> >> On Sat, Dec 22, 2012 at 12:29 AM, Christoph Hellwig <hch@...radead.org> wrote:
> >> > NAK, we went through great trouble to get rid of the nasty layering
> >> > violation where the VM called file_update_time directly just a short
> >> > while ago, reintroducing that is a massive step back.
> >> >
[...]
> >With the call from
> > remove_vma() it is more problematic (and the calling context there is
> > harder as well because we hold mmap_sem). We could maybe leave the call
> > upto filesystem's ->release callback (and provide generic ->release handler
> > which just calls mapping_flush_cmtime()). It won't be perfect because that
> > gets called only after the last file descriptor for that struct file is
> > closed (i.e., if a process forks and child inherits mappings, ->release gets
> > called only after both parent and the child unmap the file) but it should
> > catch 99% of the real world cases. Christoph, would the be OK with
> > you?
> 
> I'm not sure that 99% is good enough -- I'd be nervous about breaking
> some build or versioning system.
> 
> vm_ops->close is almost a good place for this, except that it's called
> on some failure paths and it will mess up is_mergeable_vma if lots of
> filesystems suddenly have a ->close operation.  What about adding
> vm_ops->flush, which would be called in remove_vma and possibly
> msync(MS_ASYNC)?  I think that all real filesystems (i.e. things that
> care about cmtime updates) have vm_operations.
  Yeah, that could work. I'm still somewhat nervous about updating the time
stamp under mmap_sem but in ->page_mkwrite we were in the same situation so
I guess it's fine.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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