From: Mingming Cao <cmm@us.ibm.com>
Subject: Re: [PATCH] ext4: Use page_mkwrite vma_operations to get mmap
	write notification.
Date: Fri, 22 Feb 2008 11:28:43 -0800
Message-ID: <1203708523.3639.22.camel@localhost.localdomain>
References: <1203691158-6788-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
	 <1203703848.3639.9.camel@localhost.localdomain>
	 <20080222182310.GC6629@skywalker>
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Cc: tytso@mit.edu, linux-ext4@vger.kernel.org
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
In-Reply-To: <20080222182310.GC6629@skywalker>
Sender: linux-ext4-owner@vger.kernel.org

On Fri, 2008-02-22 at 23:53 +0530, Aneesh Kumar K.V wrote:
> On Fri, Feb 22, 2008 at 10:10:48AM -0800, Mingming Cao wrote:
> > On Fri, 2008-02-22 at 20:09 +0530, Aneesh Kumar K.V wrote:
> 
> .....
> 
> > > +		ext4_journal_stop(handle);
> > > +		goto out_unlock;
> > > +	}
> > > +	if (!ret && ext4_should_order_data(inode)) {
> > > +		ret = walk_page_buffers(handle, page_buffers(page),
> > > +					0, end, NULL, ext4_journal_dirty_data);
> > > +	}
> > > +	if (!ret)
> > > +		ret = block_commit_write(page, 0, end);
> > > +
> > Hmm, it seems wired to do commit_write when the page is about becoming
> > writable, but maybe that's the way it needs to?
> > 
> > Don't we need to update the i_size somewhere?
> 
ah, i_size didn't change with mapped IO.

> block_commit_write simply iterate over buffer_head of page and mark them
> dirty. That is why we don't want to call that for data=journalled mode.
> 

Right, but it still seems odd to mark the buffer_heard dirty *before*
the write happens.

I am confused, if i_size is not changing, then what we are journalling
about?  Keep journal ordering? but we haven't write anything yet....

Mingming
> > 
> > > +	ext4_journal_stop(handle);
> > > +out_unlock:
> > > +	unlock_page(page);
> > > +	mutex_unlock(&inode->i_mutex);
> > > +	return ret;
> > > +}
> > 
> > It seems this combined the three journalling mode prepare_write() code
> > here:( 
> > 
> > Since prepare_write() and commit_write() is going to sunset, why not
> > simply calling mappings->a_ops->write_begin() and then write_end()? that
> > should take care of pretty much the journalling and the page operations,
> > no?
> 
> write_begin and write_end works with the user space buffer. In this case
> we don't have one. Also what ext4_page_mkwrite does is mostly what
> write_begin/write_end does except the copy of user space buffer.
> 
> 
> -aneesh