linux-kernel - Re: [PATCH v2] f2fs: modify f2fs_is_checkpoint_ready logic to allow more data to be written with the CP disable

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Message-ID: <88cc50d5-b793-4faa-b29e-b9cf291dadde@kernel.org>
Date: Wed, 23 Oct 2024 09:50:13 +0800
From: Chao Yu <chao@...nel.org>
To: Qi Han <hanqi@...o.com>, jaegeuk@...nel.org
Cc: Chao Yu <chao@...nel.org>, linux-f2fs-devel@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: modify f2fs_is_checkpoint_ready logic to allow
 more data to be written with the CP disable

On 2024/10/22 17:15, 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=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
> 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

'dd if=/dev/zero of=./file bs=1M count=20' will be more quick to
trigger SSR allocation.

> 
> 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 | 19 +++++++++++++++++++
>   1 file changed, 19 insertions(+)
> 
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index 71adb4a43bec..b7af84a07435 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -637,12 +637,31 @@ 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)
> +{
> +	long long total_free_blocks = 0;
> +	block_t avail_user_block_count;

long long avail_user_block_count;

> +	block_t valid_block_count;
> +
> +	spin_lock(&sbi->stat_lock);
> +
> +	avail_user_block_count = get_available_block_count(sbi, NULL, true);
> +	valid_block_count = valid_user_blocks(sbi);
> +	total_free_blocks = avail_user_block_count - valid_block_count;

total_free_blocks =
	avail_user_block_count - (long long)valid_user_blocks(sbi);

Then, we can avoid allocating & assigning valid_block_count variable.

> +
> +	spin_unlock(&sbi->stat_lock);
> +
> +	return (total_free_blocks > 0) ? true : false;

return total_free_blocks > 0;

Thanks,

> +}
> +
>   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_free_blks(sbi)))
> +		return true;
>   	return false;
>   }
>