linux-kernel - Re: [PATCH 13/21] ext4: remove dead check in mb_buddy_mark

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Date:   Fri, 17 Feb 2023 09:24:43 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca, jack@...e.cz,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/21] ext4: remove dead check in mb_buddy_mark_free



on 2/14/2023 3:50 AM, Ojaswin Mujoo wrote:
> On Fri, Feb 10, 2023 at 03:48:17AM +0800, Kemeng Shi wrote:
>> We always adjust first to even number and adjust last to odd number, so
>> first == last will never happen. Remove this dead check.
>>
>> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
>> ---
>>  fs/ext4/mballoc.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>> index bdabe0d81d4a..0fdbf16ac180 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -1718,7 +1718,8 @@ static void mb_buddy_mark_free(struct ext4_buddy *e4b, int first, int last)
>>  			break;
>>  		order++;
>>  
>> -		if (first == last || !(buddy2 = mb_find_buddy(e4b, order, &max))) {
>> +		buddy2 = mb_find_buddy(e4b, order, &max);
>> +		if (!buddy2) {
>>  			mb_clear_bits(buddy, first, last - first + 1);
>>  			e4b->bd_info->bb_counters[order - 1] += last - first + 1;
>>  			break;
>> -- 
>> 2.30.0
>>
> Okay, so I checked the code and seems like you are right. There is can't be any
> scenario where (first == last) after the calls to mb_buddy_adjust_border().
> 
> However, I'm a bit hesitant to give my Reviewed by since buddy algo is still a
> bit confusing to me and I might be missing some weird edge case.  Maybe someone
> can help double check this.
Hi, could anyone help double check this patch and patch 18/21 "ext4: remove
unnecessary goto in ext4_mb_mark_diskspace_used" in the same patchset. Thanks.

-- 
Best wishes
Kemeng Shi