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

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 05/11, changfengnan@vivo.com wrote:
> Hi Jaegeuk:
> 
> If there're existing clusters beyond i_size, may cause data corruption, but
> will this happen in normal? maybe some error can cause this, if i_size is
> error the data beyond size still can't handle properly.  Is there normal
> case can casue existing clusters beyond i_size?

We don't have a rule to sync between i_size and i_blocks.

> 
> Thanks.
> 
> -----邮件原件-----
> 发件人: Jaegeuk Kim <jaegeuk@kernel.org> 
> 发送时间: 2021年5月10日 23:44
> 收件人: Fengnan Chang <changfengnan@vivo.com>
> 抄送: chao@kernel.org; linux-f2fs-devel@lists.sourceforge.net
> 主题: Re: [PATCH v4] f2fs: compress: avoid unnecessary check in
> f2fs_prepare_compress_overwrite
> 
> 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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