linux-ext4 - Re: [PATCH 1/2] block: add BH

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Message-ID: <87wr4f1qsm.fsf@sejong.aot.lge.com>
Date:	Mon, 14 May 2012 10:42:49 +0900
From:	Namhyung Kim <namhyung.kim@....com>
To:	Saugata Das <saugata.das@...ricsson.com>
Cc:	<linux-ext4@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<tytso@....edu>, <adilger@...mcloud.com>, <hch@...radead.org>,
	<arnd.bergmann@...aro.org>, <venkat@...aro.org>,
	Saugata Das <saugata.das@...aro.org>
Subject: Re: [PATCH 1/2] block: add BH_Meta flag

Hi,

On Fri, 11 May 2012 20:32:56 +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. This patch adds the capability to add REQ_META flag
> during meta data write.
>

AFAIK, the REQ_META is only for marking a bio/req to be recognized when
using blktrace or something. You can use REQ_PRIO for the purpose but it
applies only if your ioscheduler is CFQ.

But I'm not aware how the MMC stack works, so I might be missing something.

Thanks,
Namhyung


> Signed-off-by: Saugata Das <saugata.das@...aro.org>
> ---
>  fs/buffer.c                 |   10 ++++++++--
>  include/linux/buffer_head.h |    2 ++
>  2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 36d6665..688b38b 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1685,7 +1685,10 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
>  	do {
>  		struct buffer_head *next = bh->b_this_page;
>  		if (buffer_async_write(bh)) {
> -			submit_bh(write_op, bh);
> +			if (buffer_meta(bh))
> +				submit_bh(write_op | REQ_META, bh);
> +			else
> +				submit_bh(write_op, bh);
>  			nr_underway++;
>  		}
>  		bh = next;
> @@ -1739,7 +1742,10 @@ recover:
>  		struct buffer_head *next = bh->b_this_page;
>  		if (buffer_async_write(bh)) {
>  			clear_buffer_dirty(bh);
> -			submit_bh(write_op, bh);
> +			if (buffer_meta(bh))
> +				submit_bh(write_op | REQ_META, bh);
> +			else
> +				submit_bh(write_op, bh);
>  			nr_underway++;
>  		}
>  		bh = next;
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index ef26043..0776564 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -34,6 +34,7 @@ enum bh_state_bits {
>  	BH_Write_EIO,	/* I/O error on write */
>  	BH_Unwritten,	/* Buffer is allocated on disk but not written */
>  	BH_Quiet,	/* Buffer Error Prinks to be quiet */
> +	BH_Meta,	/* Is meta */
>  
>  	BH_PrivateStart,/* not a state bit, but the first bit available
>  			 * for private allocation by other entities
> @@ -126,6 +127,7 @@ BUFFER_FNS(Delay, delay)
>  BUFFER_FNS(Boundary, boundary)
>  BUFFER_FNS(Write_EIO, write_io_error)
>  BUFFER_FNS(Unwritten, unwritten)
> +BUFFER_FNS(Meta, meta)
>  
>  #define bh_offset(bh)		((unsigned long)(bh)->b_data & ~PAGE_MASK)
>  #define touch_buffer(bh)	mark_page_accessed(bh->b_page)
--
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