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

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Date:	Fri, 2 Mar 2012 01:34:31 +0530
From:	Saugata Das <saugata.das@...aro.org>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	Saugata Das <saugata.das@...ricsson.com>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	arnd.bergmann@...aro.org, adilger@...mcloud.com
Subject: Re: [PATCH] REQ_META set during meta data write

On 2 March 2012 00:03, Ted Ts'o <tytso@....edu> wrote:
> 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?

Sure, I will modify this in the next version.

>
>                                        - Ted
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