linux-kernel - Re: [PATCH v3] f2fs: modify f2fs_is_checkpoint_ready logic to allow more data to be written with the CP disable

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Message-ID: <12559def-2ca2-4e4d-851c-6ae906b6a2d7@kernel.org>
Date: Wed, 23 Oct 2024 16:06:56 +0800
From: Chao Yu <chao@...nel.org>
To: 韩棋 <hanqi@...o.com>,
 "jaegeuk@...nel.org" <jaegeuk@...nel.org>
Cc: Chao Yu <chao@...nel.org>,
 "linux-f2fs-devel@...ts.sourceforge.net"
 <linux-f2fs-devel@...ts.sourceforge.net>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Zhiguo Niu <niuzhiguo84@...il.com>
Subject: Re: [PATCH v3] f2fs: modify f2fs_is_checkpoint_ready logic to allow
 more data to be written with the CP disable

On 2024/10/23 15:40, 韩棋 wrote:
> 在 2024/10/23 10:59, Qi Han 写道:
>> 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=65
>> mkfs.f2fs -f f2fs.img
>> mount f2fs.img f2fs_dir -o checkpoint=disable:10%
>> cd f2fs_dir
>> i=1 ; while [[ $i -lt 50 ]] ; do (file_name=./2M_file$i ; dd \
>> if=/dev/random of=$file_name bs=1M count=2); i=$((i+1)); done
>> sync
>> i=1 ; while [[ $i -lt 50 ]] ; do (file_name=./2M_file$i ; truncate \
>> -s 1K $file_name); i=$((i+1)); done
>> sync
>> dd if=/dev/zero of=./file bs=1M count=20
>>
>> 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,
>> 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?
>>
>> Signed-off-by: Qi Han <hanqi@...o.com>
>> ---
>>    fs/f2fs/segment.h | 17 +++++++++++++++++
>>    1 file changed, 17 insertions(+)
>>
>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>> index 71adb4a43bec..20b568eaa95e 100644
>> --- a/fs/f2fs/segment.h
>> +++ b/fs/f2fs/segment.h
>> @@ -637,12 +637,29 @@ 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_free_blks(struct f2fs_sb_info *sbi)
>> +{
>> +	unsigned int total_free_blocks = 0;
>> +	unsigned int avail_user_block_count;



>> +
>> +	spin_lock(&sbi->stat_lock);
>> +
>> +	avail_user_block_count = get_available_block_count(sbi, NULL, true);
>> +	total_free_blocks = avail_user_block_count - (unsigned int)valid_user_blocks(sbi);
>> +
>> +	spin_unlock(&sbi->stat_lock);
>> +
>> +	return total_free_blocks > 0;
>> +}
>> +
>>    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;
> 
> Hi, Chao,
> 
> After Zhiguo's reminder, I just saw your previous patch:
> f2fs: fix to account dirty data in __get_secs_required(),
> the current modification may still return true if the segment
> is found to be insufficient when LFS and CP is closed, should
> I add the LFS mode restriction here?

Hi Qi,

I guess so, I think we need to add a lfs_mode check condition in
has_enough_free_blks(), otherwise this patch will trigger system
panic w/ below testcase:

https://lore.kernel.org/fstests/20241015025106.3203676-1-chao@kernel.org/

Thanks,

> 
> Thanks.
> 
>> +	if (likely(has_enough_free_blks(sbi)))
>> +		return true;
>>    	return false;
>>    }
>>    
>