linux-ext4 - Re: [PATCH] ext4: Fix delalloc sync hang with journal lock inversion

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Message-ID: <20080611124157.GB8121@duck.suse.cz>
Date:	Wed, 11 Jun 2008 14:41:57 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	cmm@...ibm.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix delalloc sync hang with journal lock
	inversion

On Fri 06-06-08 00:49:09, Aneesh Kumar K.V wrote:
> On Thu, Jun 05, 2008 at 06:22:09PM +0200, Jan Kara wrote:
> >   I like it. I'm only not sure whether there cannot be two users of
> > write_cache_pages() operating on the same mapping at the same time. Because
> > then they could alter writeback_index under each other and that would
> > probably result in unpleasant behavior. I think there can be two parallel
> > calls for example from sync_single_inode() and sync_page_range().
> >   In that case we'd need something like writeback_index inside wbc (or
> > maybe just alter range_start automatically when range_cont is set?) so that
> > parallel callers do no influence each other.
> > 
> 
> commit e56edfdeea0d336e496962782f08e1224a101cf2
> Author: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> Date:   Fri Jun 6 00:47:35 2008 +0530
> 
>     mm: Add range_cont mode for writeback.
>     
>     Filesystems like ext4 needs to start a new transaction in
>     the writepages for block allocation. This happens with delayed
>     allocation and there is limit to how many credits we can request
>     from the journal layer. So we call write_cache_pages multiple
>     times with wbc->nr_to_write set to the maximum possible value
>     limitted by the max journal credits available.
>     
>     Add a new mode to writeback that enables us to handle this
>     behaviour. If mapping->writeback_index is not set we use
>     wbc->range_start to find the start index and then at the end
>     of write_cache_pages we store the index in writeback_index. Next
>     call to write_cache_pages will start writeout from writeback_index.
>     Also we limit writing to the specified wbc->range_end.
  I think this changelog is out of date...

>     Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> 
> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> index f462439..0d8573e 100644
> --- a/include/linux/writeback.h
> +++ b/include/linux/writeback.h
> @@ -63,6 +63,7 @@ struct writeback_control {
>  	unsigned for_writepages:1;	/* This is a writepages() call */
>  	unsigned range_cyclic:1;	/* range_start is cyclic */
>  	unsigned more_io:1;		/* more io to be dispatched */
> +	unsigned range_cont:1;
>  };
>  
>  /*
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 789b6ad..182233b 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -882,6 +882,9 @@ int write_cache_pages(struct address_space *mapping,
>  	if (wbc->range_cyclic) {
>  		index = mapping->writeback_index; /* Start from prev offset */
>  		end = -1;
> +	} else if (wbc->range_cont) {
> +		index = wbc->range_start >> PAGE_CACHE_SHIFT;
> +		end = wbc->range_end >> PAGE_CACHE_SHIFT;
  Hmm, why isn't this in the next else?

>  	} else {
>  		index = wbc->range_start >> PAGE_CACHE_SHIFT;
>  		end = wbc->range_end >> PAGE_CACHE_SHIFT;
> @@ -956,6 +959,9 @@ int write_cache_pages(struct address_space *mapping,
>  	}
>  	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
>  		mapping->writeback_index = index;
> +
> +	if (wbc->range_cont)
> +		wbc->range_start = index << PAGE_CACHE_SHIFT;
>  	return ret;
>  }
>  EXPORT_SYMBOL(write_cache_pages);

									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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