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Date:	Tue, 24 Jun 2008 15:58:38 -0700
From:	Mingming <cmm@...ibm.com>
To:	Holger Kiehl <Holger.Kiehl@....de>
Cc:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Theodore Tso <tytso@....edu>,
	Eric Sandeen <sandeen@...hat.com>, Jan Kara <jack@...e.cz>,
	Solofo.Ramangalahy@...l.net, Nick Dokos <nicholas.dokos@...com>,
	linux-ext4@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Performance of ext4


On Tue, 2008-06-24 at 21:12 +0000, Holger Kiehl wrote:
> On Tue, 24 Jun 2008, Aneesh Kumar K.V wrote:
> 
> > On Tue, Jun 24, 2008 at 08:37:21AM +0530, Aneesh Kumar K.V wrote:
> >> On Mon, Jun 23, 2008 at 05:31:32PM -0700, Mingming wrote:
> >>>
> >>> On Mon, 2008-06-23 at 23:15 +0530, Aneesh Kumar K.V wrote:
> >>>
> >>>> I found one place where we fail to update i_disksize. Can you try this
> >>>> patch ?
> >>>>
> >>>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> >>>> index 33f940b..9fa737f 100644
> >>>> --- a/fs/ext4/inode.c
> >>>> +++ b/fs/ext4/inode.c
> >>>> @@ -1620,7 +1620,10 @@ static int ext4_da_writepage(struct page *page,
> >>>>  	loff_t size;
> >>>>  	unsigned long len;
> >>>>  	handle_t *handle = NULL;
> >>>> +	ext4_lblk_t block;
> >>>> +	loff_t disksize;
> >>>>  	struct buffer_head *page_bufs;
> >>>> +	struct buffer_head *bh, *head;
> >>>>  	struct inode *inode = page->mapping->host;
> >>>>
> >>>>  	handle = ext4_journal_current_handle();
> >>>> @@ -1662,6 +1665,38 @@ static int ext4_da_writepage(struct page *page,
> >>>>  	else
> >>>>  		ret = block_write_full_page(page, ext4_da_get_block_write, wbc);
> >>>>
> >>>> +	 if (ret)
> >>>> +		 return ret;
> >>>> +	/*
> >>>> +	 * When called via shrink_page_list and if we don't have any unmapped
> >>>> +	 * buffer_head we still could have written some new content in an
> >>>> +	 * already mapped buffer. That means we need to extent i_disksize here
> >>>> +	 */
> >>>
> >>> In this case(when extend the file without need block allocation),
> >>> wouldn't make sense to update the i_disksize at write_end() time? So
> >>> that the window of i_size different from i_disksize could be much
> >>> smaller in this case.
> >>>
> >>>
> >>> Something like below? (untested)
> >>
> >> In this case you will have to start a transaction in write_begin . With
> >> the below code transaction is started inside page_lock. Also I don't
> >> think we need needed_blocks credit just 1 should be enough because we
> >> are not doing any block allocation here. We just need to update the
> >> inode block.
> >>
> >>
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 33f940b..bc925c5 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -1770,6 +1770,7 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
> > 	struct page *page;
> > 	pgoff_t index;
> > 	unsigned from, to;
> > +	handle_t *handle;
> > 	struct inode *inode = mapping->host;
> >
> > 	index = pos >> PAGE_CACHE_SHIFT;
> > @@ -1777,6 +1778,17 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
> > 	to = from + len;
> >
> > retry:
> > +	/*
> > +	 * If we are writing towards the end of an already mapped
> > +	 * buffer_head, we don't do any block allocation. But we
> > +	 * need to update i_disksize.
> > +	 */
> > +	handle = ext4_journal_start(inode, 1);
> > +	if (IS_ERR(handle)) {
> > +		ret = PTR_ERR(handle);
> > +		goto out;
> > +	}
> > +
> > 	page = __grab_cache_page(mapping, index);
> > 	if (!page)
> > 		return -ENOMEM;
> > @@ -1786,15 +1798,63 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
> > 							ext4_da_get_block_prep);
> > 	if (ret < 0) {
> > 		unlock_page(page);
> > +		ext4_journal_stop(handle);
> > 		page_cache_release(page);
> > 	}
> >
> > 	if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
> > 		goto retry;
> >
> > +out:
> > 	return ret;
> > }
> >
> > +static int ext4_da_write_end(struct file *file,
> > +				struct address_space *mapping,
> > +				loff_t pos, unsigned len, unsigned copied,
> > +				struct page *page, void *fsdata)
> > +{
> > +	loff_t new_i_size;
> > +	unsigned from, to;
> > +	int ret = 0, ret2;
> > +	struct inode *inode = mapping->host;
> > +	handle_t *handle = ext4_journal_current_handle();
> > +
> > +	from = pos & (PAGE_CACHE_SIZE - 1);
> > +	to = from + len;
> > +
> > +	/*
> > +	 * generic_write_end() will run mark_inode_dirty() if i_size
> > +	 * changes.  So let's piggyback the i_disksize mark_inode_dirty
> > +	 * into that.
> > +	 */
> > +
> > +	new_i_size = pos + copied;
> > +	if (new_i_size > EXT4_I(inode)->i_disksize)
> > +		if (!walk_page_buffers(NULL, page_buffers(page),
> > +					0, len, NULL,
> > +					ext4_bh_unmapped_or_delay)) {
> > +			/*
> > +			 * Updating i_disksize when extending file without
> > +			 * need block allocation
> > +			 */
> > +			if (ext4_should_order_data(inode))
> > +				ret = ext4_jbd2_file_inode(handle, inode);
> > +
> > +			EXT4_I(inode)->i_disksize = new_i_size;
> > +		}
> > +	ret2 = generic_write_end(file, mapping, pos,
> > +			len, copied, page, fsdata);
> > +	copied = ret2;
> > +	if (ret2 < 0)
> > +		ret = ret2;
> > +	ret2 = ext4_journal_stop(handle);
> > +	if (!ret)
> > +		ret = ret2;
> > +
> > +	return ret ? ret : copied;
> > +}
> > +
> > static void ext4_da_invalidatepage(struct page *page, unsigned long offset)
> > {
> > 	/*
> > @@ -2250,7 +2310,7 @@ static int ext4_journalled_set_page_dirty(struct page *page)
> > 	.writepages	= ext4_da_writepages,
> > 	.sync_page	= block_sync_page,
> > 	.write_begin	= ext4_da_write_begin,
> > -	.write_end	= generic_write_end,
> > +	.write_end	= ext4_da_write_end,
> > 	.bmap		= ext4_bmap,
> > 	.invalidatepage	= ext4_da_invalidatepage,
> > 	.releasepage	= ext4_releasepage,
> >
> Yes, with this patch applied on top of latest patch queue I no longer
> get truncated files, after running a short test. Tomorrow I will do some
> more thorough testing and use the patch you have send to me in a separate
> mail. The above patch did not apply but it was easy to apply by hand.


Thanks for quick response and test. I have updated the patch queue with
above patch merged. Please let me know if you still see apply issue and
file size update issue with current patch queue.

Regards,
Mingming


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