linux-kernel - Re: [PATCH 6/6] writeback: remove unneeded GDTC_INIT_NO

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Date: Tue, 26 Mar 2024 13:35:03 +0100
From: Jan Kara <jack@...e.cz>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: akpm@...ux-foundation.org, tj@...nel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	willy@...radead.org, bfoster@...hat.com, jack@...e.cz,
	dsterba@...e.com, mjguzik@...il.com, dhowells@...hat.com,
	peterz@...radead.org
Subject: Re: [PATCH 6/6] writeback: remove unneeded GDTC_INIT_NO_WB

On Wed 20-03-24 19:02:22, Kemeng Shi wrote:
> We never use gdtc->dom set with GDTC_INIT_NO_WB, just remove unneeded
> GDTC_INIT_NO_WB
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>

Please no, this leaves a trap for the future. If anything, I'd teach
GDTC_INIT() that 'wb' can be NULL and replace GDTC_INIT_NO_WB with
GDTC_INIT(NULL).

								Honza

> ---
>  mm/page-writeback.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 481b6bf34c21..09b2b0754cc5 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -154,8 +154,6 @@ struct dirty_throttle_control {
>  				.dom = &global_wb_domain,		\
>  				.wb_completions = &(__wb)->completions
>  
> -#define GDTC_INIT_NO_WB		.dom = &global_wb_domain
> -
>  #define MDTC_INIT(__wb, __gdtc)	.wb = (__wb),				\
>  				.dom = mem_cgroup_wb_domain(__wb),	\
>  				.wb_completions = &(__wb)->memcg_completions, \
> @@ -210,7 +208,6 @@ static void wb_min_max_ratio(struct bdi_writeback *wb,
>  
>  #define GDTC_INIT(__wb)		.wb = (__wb),                           \
>  				.wb_completions = &(__wb)->completions
> -#define GDTC_INIT_NO_WB
>  #define MDTC_INIT(__wb, __gdtc)
>  
>  static bool mdtc_valid(struct dirty_throttle_control *dtc)
> @@ -438,7 +435,7 @@ static void domain_dirty_limits(struct dirty_throttle_control *dtc)
>   */
>  void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
>  {
> -	struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
> +	struct dirty_throttle_control gdtc = { };
>  
>  	gdtc.avail = global_dirtyable_memory();
>  	domain_dirty_limits(&gdtc);
> @@ -895,7 +892,7 @@ unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
>  
>  unsigned long wb_calc_cg_thresh(struct bdi_writeback *wb)
>  {
> -	struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
> +	struct dirty_throttle_control gdtc = { };
>  	struct dirty_throttle_control mdtc = { MDTC_INIT(wb, &gdtc) };
>  	unsigned long filepages, headroom, writeback;
>  
> -- 
> 2.30.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR