Message-ID: <938a8e61-4e47-1acc-938c-c90d213d2c86@kernel.org>
Date:   Wed, 1 Feb 2023 20:57:33 +0800
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To:     qixiaoyu <qxy65535@gmail.com>, Jaegeuk Kim <jaegeuk@kernel.org>
Cc:     xiongping1@xiaomi.com, qixiaoyu1@xiaomi.com,
        linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
References: <20230113125859.15651-1-qixiaoyu1@xiaomi.com>
 <20230116030850.20260-1-qixiaoyu1@xiaomi.com>
 <7c12ebaa-4d3d-e475-dfb2-7b459cd26e64@kernel.org>
 <Y9ZWDVV3HJ431Fis@mi-HP-ProDesk-680-G4-MT>
 <Y9pZqOMBipT2NZk0@mi-HP-ProDesk-680-G4-MT>
From:   Chao Yu <chao@kernel.org>
Subject: Re: [PATCH 1/2 v2] f2fs: fix wrong calculation of block age
In-Reply-To: <Y9pZqOMBipT2NZk0@mi-HP-ProDesk-680-G4-MT>
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On 2023/2/1 20:23, qixiaoyu wrote:
>>>
>>> How about updating as below to avoid lossing accuracy if new is less than 100?
>>>
>>> return div_u64(new * (100 - LAST_AGE_WEIGHT), 100) +
>>> 		div_u64(old * LAST_AGE_WEIGHT, 100);
>>>
>>> Thanks,
>>>
>>
>> We want to avoid overflow by doing the division first. To keep the accuracy, how

Alright,

>> about updating as below:
>>
>> 	res = div_u64_rem(new, 100, &rem_new) * (100 - LAST_AGE_WEIGHT)
>> 		+ div_u64_rem(old, 100, &rem_old) * LAST_AGE_WEIGHT;
>> 	res += rem_new * (100 - LAST_AGE_WEIGHT) / 100 + rem_old * LAST_AGE_WEIGHT / 100;
>> 	return res;

if (rem_new)
	res += rem_new * (100 - LAST_AGE_WEIGHT) / 100;
if (rem_old)
	res += rem_old * LAST_AGE_WEIGHT / 100;

Otherwise, it looks fine to me. :)

Thanks,

>>
>> Thanks,
>>
> 
> Friendly ping
> 
>>>>    }
>>>>    /* This returns a new age and allocated blocks in ei */