Re: [f2fs-dev] [PATCH v4] f2fs: compress: avoid unnecessary check in f2fs_prepare_compress_overwrite

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 05/07, Fengnan Chang wrote:
> when write compressed file with O_TRUNC, there will be a lot of
> unnecessary check valid blocks in f2fs_prepare_compress_overwrite,
> especially when written in page size, remove it.
> 
> This patch will not bring significant performance improvements, I test
> this on mobile phone, use androbench, the sequential write test case was
> open file with O_TRUNC, set write size to 4KB,  performance improved
> about 2%-3%. If write size set to 32MB, performance improved about 0.5%.
> 
> Signed-off-by: Fengnan Chang <changfengnan@vivo.com>
> ---
>  fs/f2fs/data.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index cf935474ffba..b9ec7b182f45 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -3303,9 +3303,17 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
>  #ifdef CONFIG_F2FS_FS_COMPRESSION
>  	if (f2fs_compressed_file(inode)) {
>  		int ret;
> +		pgoff_t end = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
> 
>  		*fsdata = NULL;
> 
> +		/*
> +		 * when write pos is bigger than inode size ,f2fs_prepare_compress_overwrite
> +		 * always return 0, so check pos first to avoid this.
> +		 */
> +		if (index >= end)
> +			goto repeat;

What if there're existing clusters beyond i_size? Given performance impacts,
do we really need this?

> +
>  		ret = f2fs_prepare_compress_overwrite(inode, pagep,
>  							index, fsdata);
>  		if (ret < 0) {
> --
> 2.29.0


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