linux-ext4 - Re: [PATCH] jbd2: avoid the concurrent data writeback

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Date:	Tue, 16 Nov 2010 16:13:37 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	"Wu, Fengguang" <fengguang.wu@...el.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] jbd2: avoid the concurrent data writeback

Hi Hellwig,

On Mon, 15 Nov 2010 19:27:32 +0800
Christoph Hellwig <hch@...radead.org> wrote:

> On Mon, Nov 15, 2010 at 05:59:43PM +0800, Feng Tang wrote:
> > + *
> > + * Sometimes when this get called, the host inode may be under data
> > + * syncing initiated by flush thread(especially for a large file),
> > and 
> > + * in such situation, we should skip this path of writeback
> >   */
> >  static int journal_submit_inode_data_buffers(struct address_space
> > *mapping) {
> > @@ -181,6 +185,13 @@ static int
> > journal_submit_inode_data_buffers(struct address_space
> > *mapping) .range_end = i_size_read(mapping->host), };
> >  
> > +	spin_lock(&inode_lock);
> > +	if (mapping->host->i_state & I_SYNC) {
> > +		spin_unlock(&inode_lock);
> > +		return 0;
> > +	}
> > +	spin_unlock(&inode_lock);
> > +
> 
> inode_lock is not exported to modules, and that's for a pretty good
> reason.  I think you want to change this code at a higher level to not
> compete with the flusher threads at all.
> 
Good point. The alternative I can think of is to use writeback_in_progress(),
thus the check will be changed to:

	if (writeback_in_progress(mapping->backing_dev_info))
		return 0;
This have the same effect as the original patch.


Thanks,
Feng
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