linux-kernel - Re: [PATCH v2 01/12] md/raid5: Factor out ahead_of

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Date:   Wed, 27 Apr 2022 09:28:33 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
        Song Liu <song@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Stephen Bates <sbates@...thlin.com>,
        Martin Oliveira <Martin.Oliveira@...eticom.com>,
        David Sloan <David.Sloan@...eticom.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 01/12] md/raid5: Factor out ahead_of_reshape() function



On 4/21/22 3:54 AM, Logan Gunthorpe wrote:
> There are a few uses of an ugly ternary operator in raid5_make_request()
> to check if a sector is a head of a reshape sector.
>
> Factor this out into a simple helper called ahead_of_reshape().
>
> This appears to fix the first bio_wouldblock_error() check which appears
> to have comparison operators that didn't match the check below which
> causes a schedule. Besides this, no functional changes intended.
>
> Suggested-by: Christoph Hellwig<hch@....de>
> Signed-off-by: Logan Gunthorpe<logang@...tatee.com>
> ---
>   drivers/md/raid5.c | 29 +++++++++++++++++------------
>   1 file changed, 17 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 7f7d1546b9ba..97b23c18402b 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -5787,6 +5787,15 @@ static void make_discard_request(struct mddev *mddev, struct bio *bi)
>   	bio_endio(bi);
>   }
>   
> +static bool ahead_of_reshape(struct mddev *mddev, sector_t sector,
> +			     sector_t reshape_sector)
> +{
> +	if (mddev->reshape_backwards)
> +		return sector < reshape_sector;
> +	else
> +		return sector >= reshape_sector;
> +}

I think it can be an inline function.

> +
>   static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>   {
>   	struct r5conf *conf = mddev->private;
> @@ -5843,9 +5852,8 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>   	/* Bail out if conflicts with reshape and REQ_NOWAIT is set */
>   	if ((bi->bi_opf & REQ_NOWAIT) &&
>   	    (conf->reshape_progress != MaxSector) &&
> -	    (mddev->reshape_backwards
> -	    ? (logical_sector > conf->reshape_progress && logical_sector <= conf->reshape_safe)
> -	    : (logical_sector >= conf->reshape_safe && logical_sector < conf->reshape_progress))) {
> +	    !ahead_of_reshape(mddev, logical_sector, conf->reshape_progress) &&
> +	    ahead_of_reshape(mddev, logical_sector, conf->reshape_safe)) {

TBH, the previous code is more readable to me though I can live with the 
change.

Thanks,
Guoqing