linux-kernel - Re: [PATCH] btrfs: remove the useless value assignment in block_rsv_release

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Date:   Tue, 17 Nov 2020 11:17:17 +0800
From:   kaixuxia <xiakaixu1987@...il.com>
To:     dsterba@...e.cz, dsterba@...e.com
Cc:     clm@...com, josef@...icpanda.com, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kaixu Xia <kaixuxia@...cent.com>
Subject: Re: [PATCH] btrfs: remove the useless value assignment in
 block_rsv_release_bytes



On 2020/11/16 23:15, David Sterba wrote:
> On Sun, Nov 15, 2020 at 02:39:23PM +0800, xiakaixu1987@...il.com wrote:
>> From: Kaixu Xia <kaixuxia@...cent.com>
>>
>> The variable qgroup_to_release is overwritten by the following if/else
>> statement before it is used, so this assignment is useless. Remove it.
> 
> Again this lacks explanation why removing it is correct.
> 
Actually this assignment is redundant because the variable qgroup_to_release
has been overwritten before it is used. The logic like this,

 static u64 block_rsv_release_bytes(...)
 {
 ...
        if (num_bytes == (u64)-1) {
                num_bytes = block_rsv->size;
                qgroup_to_release = block_rsv->qgroup_rsv_size;
        }   
        
	//qgroup_to_release isn't used

        if (block_rsv->qgroup_rsv_reserved >= block_rsv->qgroup_rsv_size) {
                qgroup_to_release = block_rsv->qgroup_rsv_reserved -
                                    block_rsv->qgroup_rsv_size;
                block_rsv->qgroup_rsv_reserved = block_rsv->qgroup_rsv_size;
        } else {
                qgroup_to_release = 0;
        }//qgroup_to_release is overwritten    
 ...
 }

Thanks,
Kaixu

-- 
kaixuxia