linux-ext4 - Re: [PATCH] REQ_META set during meta data write

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Date:	Thu, 1 Mar 2012 13:33:27 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Saugata Das <saugata.das@...ricsson.com>
Cc:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	saugata.das@...aro.org, arnd.bergmann@...aro.org,
	adilger@...mcloud.com
Subject: Re: [PATCH] REQ_META set during meta data write

On Thu, Mar 01, 2012 at 11:41:03PM +0530, Saugata Das wrote:
> From: Saugata Das <saugata.das@...aro.org>
> 
> Today, storage devices like eMMC has special features like data tagging
> (introduced in MMC-4.5 version) in order to improve performance of some
> specific writes. On MMC stack, data tagging is used for all writes which has
> REQ_META flag set. On EXT4, however, currently REQ_META is set only for read.
> This patch adds the capability to add REQ_META flag during meta data write.
> This patch adds new function set_buffer_meta, which is used to set a bit
> BH_Meta in the b_state field when meta data and super block is made dirty.
> 
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -2926,6 +2926,9 @@ int submit_bh(int rw, struct buffer_head * bh)
>  	if (test_set_buffer_req(bh) && (rw & WRITE))
>  		clear_buffer_write_io_error(bh);
>  
> +	if (buffer_meta(bh) && (rw & WRITE))
> +		rw |= REQ_META;
> +

I know it's not necessary for your purposes as stated in the commit
description, but wouldn't it be better if buffer_meta() always caused
REQ_META to be set, regardless of whether we are doing a read or a
write?

					- Ted
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