linux-kernel - Re: [PATCH] raid5: Retry R5_ReadNoMerge flag when hit a read error.

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Date:	Wed, 11 Sep 2013 12:42:00 +1000
From:	NeilBrown <neilb@...e.de>
To:	ycbzzjlby@...il.com
Cc:	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bian Yu <bianyu@...acom.com>
Subject: Re: [PATCH] raid5: Retry R5_ReadNoMerge flag when hit a read error.

On Sun,  1 Sep 2013 20:13:02 -0400 ycbzzjlby@...il.com wrote:

> From: Bian Yu <bianyu@...acom.com>
> 
> Because of block layer merge, one bio fails will cause other bios
> which belongs to the same request fails, so raid5_end_read_request
> will record all these bios as badblocks.
> If retry request with R5_ReadNoMerge flag to avoid bios merge,
> badblocks can only record sector which is bad exactly.
> 
> test:
> hdparm --yes-i-know-what-i-am-doing --make-bad-sector 300000 /dev/sdb
> mdadm -C /dev/md0 -l5 -n3 /dev/sd[bcd] --assume-clean
> mdadm /dev/md0 -f /dev/sdd
> mdadm /dev/md0 -r /dev/sdd
> mdadm --zero-superblock /dev/sdd
> mdadm /dev/md0 -a /dev/sdd
> 
> 1. Without this patch:
> cat /sys/block/md0/md/rd*/bad_blocks
> 299776 256
> 299776 256
> 
> 2. With this patch:
> cat /sys/block/md0/md/rd*/bad_blocks
> 300000 8
> 300000 8
> 
> Signed-off-by: Bian Yu <bianyu@...acom.com>
> ---
>  drivers/md/raid5.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index ff1aecf..ee8c280 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -1924,6 +1924,9 @@ static void raid5_end_read_request(struct bio * bi, int error)
>  			       mdname(conf->mddev), bdn);
>  		else
>  			retry = 1;
> +		if (set_bad && test_bit(In_sync, &rdev->flags)
> +		    && !test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
> +			retry = 1;
>  		if (retry)
>  			if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags)) {
>  				set_bit(R5_ReadError, &sh->dev[i].flags);


Applied, thanks.

NeilBrown

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