linux-ext4 - Re: [patch 4/8] mm: write_cache

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Date:	Fri, 10 Oct 2008 12:10:54 -0400
From:	Theodore Tso <tytso@....edu>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Steven Whitehouse <steve@...gwyn.com>, npiggin@...e.de,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mikulas Patocka <mpatocka@...hat.com>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [patch 4/8] mm: write_cache_pages type overflow fix

On Fri, Oct 10, 2008 at 09:24:47PM +0530, Aneesh Kumar K.V wrote:
> On Fri, Oct 10, 2008 at 10:08:29AM -0400, Christoph Hellwig wrote:
> > On Fri, Oct 10, 2008 at 10:05:35AM -0400, Theodore Tso wrote:
> > > 3) A version which (optionally via a flag in the wbc structure)
> > > instructs write_cache_pages() to not pursue those updates.  This has
> > > not been written yet.
> > 
> > This one sounds best to me (although we'd have to actualy see it..)
> 
> something like  the below ?
> 
> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> index bd91987..7599af2 100644
> --- a/include/linux/writeback.h
> +++ b/include/linux/writeback.h
> @@ -63,6 +63,8 @@ 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 */
> +	/* flags which control the write_cache_pages behaviour */
> +	int writeback_flags;
>  };

I don't see a definition for WB_NO_NRWRITE_UPDATE and
WB_NO_INDEX_UPDATE in your patch?

Given the structure seems to be using bitfields for all of the other
fields, why not do this instead?

	unsigned no_nrwrite_update:1;
	unsigned no_index_update:1;

Personally, I'm old school, and prefer using an int flag field and
using #define's for flags, but the rest of the structure is using
bitfields for flags, and it's probably better to be consistent...
	

							- Ted
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