linux-ext4 - Re: [PATCH, RFC] ext4: add EXT4_IOC_ALLOC_DA

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Date:	Thu, 12 Mar 2009 16:04:31 -0400
From:	Theodore Tso <tytso@....edu>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH, RFC] ext4: add EXT4_IOC_ALLOC_DA_BLKS ioctl

On Thu, Mar 12, 2009 at 11:32:18AM -0500, Eric Sandeen wrote:
> Aneesh Kumar K.V wrote:
> > On Wed, Mar 11, 2009 at 05:41:05PM -0500, Eric Sandeen wrote:
> >> Theodore Ts'o wrote:
> >>> Add an ioctl which forces all of the delay allocated blocks to be
> >>> allocated.  This also provides a function ext4_alloc_da_blocks() which
> >>> will be used by the following commits to force files to be fully
> >>> allocated to preserve application-expected ext3 behaviour.
> >>>
> >> Is it worth checking whether a) the file has delalloc blocks, and/or b)
> >> whether the mapping is dirty before we spin off a filemap_flush?
> >>
> > +int ext4_alloc_da_blocks(struct inode *inode)
> > +{
> > +       if (!EXT4_I(inode)->i_reserved_data_blocks &&
> > +           !EXT4_I(inode)->i_reserved_meta_blocks)
> > +               return 0;
> > 
> > This check test does (a). Since the ioctl is to force allocation of
> > delayed allocated blocks i guess (a) is enough because we don't want to
> > cause a filemap_flush when we don't have any delayed allocated blocks
> > but have dirty pages around.
> 
> and b) is as simple as
> 
> if (!mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY))
> 	return 0;

Yeah, but (b) isn't necessary; if there are some delayed allocation
blocks, by definition there must be some dirty pages, right?

	   	      	    	    	 - Ted
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