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Subject: Re: [f2fs-dev] [PATCH v4] f2fs: introduce fragment allocation mode
 mount option
To:     Daeho Jeong <daeho43@gmail.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
        Daeho Jeong <daehojeong@google.com>
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From:   Chao Yu <chao@kernel.org>
Message-ID: <a59d23b9-961f-4129-7491-59f88923366a@kernel.org>
Date:   Fri, 10 Sep 2021 07:50:57 +0800
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On 2021/9/8 2:12, Daeho Jeong wrote:
> On Fri, Sep 3, 2021 at 11:45 PM Chao Yu <chao@kernel.org> wrote:
>>
>> On 2021/9/4 12:40, Daeho Jeong wrote:
>>>> As a per curseg field.
>>>>
>>>>> Maybe, we run into the same race condition issue you told before for
>>>>> fragment_remained_chunk.
>>>>> Could you clarify this more?
>>>>
>>>> e.g.
>>>>
>>>> F2FS_OPTION(sbi).fs_mode = FS_MODE_FRAGMENT_FIXED_BLK
>>>> fragment_chunk_size = 384
>>>> fragment_hole_size = 384
>>>>
>>>> When creating hole:
>>>>
>>>> - f2fs_allocate_data_block
>>>>     - __refresh_next_blkoff
>>>>       chunk locates in [0, 383] of current segment
>>>>       seg->next_blkoff = 384
>>>>       sbi->fragment_remained_chunk = 0
>>>>       then we will reset sbi->fragment_remained_chunk to 384
>>>>       and move seg->next_blkoff forward to 768 (384 + 384)
>>>>     - __has_curseg_space() returns false
>>>>     - allocate_segment() allocates new current segment
>>>>
>>>> So, for such case that hole may cross two segments, hole size may be truncated
>>>> to left size of previous segment.
>>>
>>> First, sbi->fragment_remained_chunk should be seg->fragment_remained_chunk.
>>
>> Oh, correct.
>>
>>> I understand what you mean, so you mean we need to take the leftover
>>> "hole" size over to the next segment?
>>> In the example, the leftover hole size will be (384 - (512-384)). Do
>>> you want to take this over to the next segment?
>>
>> Yes, the left 256 block-sized hole should be created before next chunk
>> in next opened segment.
>>
> 
> Chao,
> 
> Do you have any decent idea to pass the left hole size to the next
> segment which will be allocated?

Daeho,

I guess we can record left hole size in seg->fragment_remained_hole.

Thanks,

> 
> Thanks,
> 
>> Thanks,
>>
>>>