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Subject: Re: [PATCH 6/6] writeback: remove unneeded GDTC_INIT_NO_WB
To: Jan Kara <jack@suse.cz>
Cc: akpm@linux-foundation.org, tj@kernel.org, linux-mm@kvack.org,
 linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
 willy@infradead.org, bfoster@redhat.com, dsterba@suse.com,
 mjguzik@gmail.com, dhowells@redhat.com, peterz@infradead.org
References: <20240320110222.6564-1-shikemeng@huaweicloud.com>
 <20240320110222.6564-7-shikemeng@huaweicloud.com>
 <20240326123503.kxyxg75xr7wk3ux3@quack3>
From: Kemeng Shi <shikemeng@huaweicloud.com>
Message-ID: <2e1ac568-1883-700c-ba41-575f5db339c2@huaweicloud.com>
Date: Tue, 26 Mar 2024 21:30:17 +0800
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on 3/26/2024 8:35 PM, Jan Kara wrote:
> 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@huaweicloud.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).
Would it be acceptable to define GDTC_INIT_NO_WB to null for now as
discussed in [1].

[1] https://lore.kernel.org/lkml/becdb16b-a318-ec05-61d2-d190541ae997@huaweicloud.com/

Thanks,
Kemeng
> 
> 								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
>>