Re: [PATCH] ext4: Use page_mkwrite vma_operations to get mmap write notification.

Mingming Cao
2008-02-22T19:29:08Z

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