linux-kernel - Re: [PATCH v3] writeback: factor out balance_wb

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Date: Tue, 11 Jun 2024 14:52:56 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: willy@...radead.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] writeback: factor out balance_wb_limits to remove
 repeated code

On Thu,  6 Jun 2024 11:35:47 +0800 Kemeng Shi <shikemeng@...weicloud.com> wrote:

> Factor out balance_wb_limits to remove repeated code
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
> ---
>  mm/page-writeback.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index bf050abd9053..f611272d3c5b 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1783,6 +1783,21 @@ static inline void wb_dirty_exceeded(struct dirty_throttle_control *dtc,
>  		((dtc->dirty > dtc->thresh) || strictlimit);
>  }
>  
> +/*
> + * The limits fileds dirty_exceeded and pos_ratio won't be updated if wb is
> + * in freerun state. Please don't use these invalid fileds in freerun case.

s/fileds/fields/.  I queued a fix for this.

> + */
> +static void balance_wb_limits(struct dirty_throttle_control *dtc,
> +			      bool strictlimit)
> +{
> +	wb_dirty_freerun(dtc, strictlimit);
> +	if (dtc->freerun)
> +		return;
> +
> +	wb_dirty_exceeded(dtc, strictlimit);
> +	wb_position_ratio(dtc);
> +}
> +
>  /*
>   * balance_dirty_pages() must be called by processes which are generating dirty
>   * data.  It looks at the number of dirty pages in the machine and will force
> @@ -1869,12 +1884,9 @@ static int balance_dirty_pages(struct bdi_writeback *wb,
>  		 * Calculate global domain's pos_ratio and select the
>  		 * global dtc by default.
>  		 */
> -		wb_dirty_freerun(gdtc, strictlimit);
> +		balance_wb_limits(gdtc, strictlimit);
>  		if (gdtc->freerun)
>  			goto free_running;

Would it be neater to do

		if (balance_wb_limits(...))
			goto free_running;

?

That would require a balance_wb_limits() comment update and probably
name change.  Just a thought.