Re: [f2fs-dev] [PATCH] f2fs: modify f2fs_is_checkpoint_ready logic to allow more data to be written with the CP disable

["韩棋 via Linux-f2fs-devel" <linux-f2fs-devel@lists.sourceforge.net>]

在 2024/10/18 9:52, Zhiguo Niu 写道:
> Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>
> 于2024年10月17日周四 17:57写道：
>> On 2024/10/9 18:27, Qi Han wrote:
>>> When the free segment is used up during CP disable, many write or
>>> ioctl operations will get ENOSPC error codes, even if there are
>>> still many blocks available. We can reproduce it in the following
>>> steps:
>>>
>>> dd if=/dev/zero of=f2fs.img bs=1M count=55
>>> mkfs.f2fs -f f2fs.img
>>> mount f2fs.img f2fs_dir -o checkpoint=disable:10%
>>> cd f2fs_dir
>>> dd if=/dev/zero of=bigfile bs=1M count=50
>>> sync
>>> rm bigfile
>>> i=1; while [[ $i -lt 10000000 ]]; do (file_name=./file$i; dd \
>>> if=/dev/random of=$file_name bs=1M count=0); i=$((i+1)); done
>>> stat -f ./
>>>
>>> In f2fs_need_SSR() function, it is allowed to use SSR to allocate
>>> blocks when CP is disabled, so in f2fs_is_checkpoint_ready function,
> Hi Chao and Qi,
> based on this comment  and codes, I have some doubts:
> unusable blocks are calculated  from  invalid blocks of Dirty segment
> in f2fs_get_unsuable_blocks then minus ovp_hole,
> but SSR is allowed when the checkpoint is disabled.
> So actually SSR can not use most invalid blocks of Dirty segments?
> Is this a contradiction?
> Thanks!

I think that in the case of a disable CP, in order to restore the data to
the state before the disable CP, SSR cannot reuse all the invalid blocks,
for example, suppose there is a fileA which occupies 10 data blocks when
the CP enable, and then we delete the fileA after the CP disable, the 10
blocks cannot be reused by SSR.

>>> can we judge the number of invalid blocks when free segment is not
>>> enough, and return ENOSPC only if the number of invalid blocks is
>>> also not enough?
>> Can you please try below patch?
>>
>>   From 38b7c97dcc55ba83de4220c3dc54c2eb66148dd5 Mon Sep 17 00:00:00 2001
>> From: Chao Yu <chao@kernel.org>
>> Date: Thu, 17 Oct 2024 17:07:05 +0800
>> Subject: [PATCH] f2fs: revalidate empty segment when checkpoint is disabled
>>
>> If checkpoint is off, let's set segment as free once all newly
>> written datas were removed.
>>
>> Signed-off-by: Chao Yu <chao@kernel.org>
>> ---
>>    fs/f2fs/segment.c | 13 ++++++++++++-
>>    1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index f8d6e601e084..9bad13d70afb 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -853,6 +853,17 @@ static void locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno)
>>          valid_blocks = get_valid_blocks(sbi, segno, false);
>>          ckpt_valid_blocks = get_ckpt_valid_blocks(sbi, segno, false);
>>
>> +       /*
>> +        * If checkpoint is off, let's set segment as free once all newly
>> +        * written datas were removed.
>> +        */
>> +       if (is_sbi_flag_set(sbi, SBI_CP_DISABLED) &&
>> +               valid_blocks == 0 && ckpt_valid_blocks == 0) {
>> +               __remove_dirty_segment(sbi, segno, DIRTY);
>> +               __set_test_and_free(sbi, segno, false);
>> +               goto out_lock;
>> +       }
>> +
>>          if (valid_blocks == 0 && (!is_sbi_flag_set(sbi, SBI_CP_DISABLED) ||
>>                  ckpt_valid_blocks == usable_blocks)) {
>>                  __locate_dirty_segment(sbi, segno, PRE);
>> @@ -863,7 +874,7 @@ static void locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno)
>>                  /* Recovery routine with SSR needs this */
>>                  __remove_dirty_segment(sbi, segno, DIRTY);
>>          }
>> -
>> +out_lock:
>>          mutex_unlock(&dirty_i->seglist_lock);
>>    }
>>
>> --
>> 2.40.1
>>
>>> Signed-off-by: Qi Han <hanqi@vivo.com>
>>> ---
>>>    fs/f2fs/segment.h | 21 +++++++++++++++++++++
>>>    1 file changed, 21 insertions(+)
>>>
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>>> index 71adb4a43bec..9bf0cf3a6a31 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -637,12 +637,33 @@ static inline bool has_enough_free_secs(struct f2fs_sb_info *sbi,
>>>        return !has_not_enough_free_secs(sbi, freed, needed);
>>>    }
>>>
>>> +static inline bool has_enough_available_blocks(struct f2fs_sb_info *sbi)
>>> +{
>>> +     unsigned int total_free_blocks = sbi->user_block_count -
>>> +                                     valid_user_blocks(sbi) -
>>> +                                     sbi->current_reserved_blocks;
>>> +
>>> +     if (total_free_blocks <= sbi->unusable_block_count)
>>> +             total_free_blocks = 0;
>>> +     else
>>> +             total_free_blocks -= sbi->unusable_block_count;
>>> +
>>> +     if (total_free_blocks > F2FS_OPTION(sbi).root_reserved_blocks)
>>> +             total_free_blocks -= F2FS_OPTION(sbi).root_reserved_blocks;
>>> +     else
>>> +             total_free_blocks = 0;
>>> +
>>> +     return (total_free_blocks > 0) ? true : false;
>>> +}
>>> +
>>>    static inline bool f2fs_is_checkpoint_ready(struct f2fs_sb_info *sbi)
>>>    {
>>>        if (likely(!is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
>>>                return true;
>>>        if (likely(has_enough_free_secs(sbi, 0, 0)))
>>>                return true;
>>> +     if (likely(has_enough_available_blocks(sbi)))
>>> +             return true;
>>>        return false;
>>>    }
>>>
>>
>>
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