linux-kernel - Re: [PATCH] f2fs: compress: remove unneed check condition

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Message-ID: <YIbyxNAaaWUiVDT9@google.com>
Date:   Mon, 26 Apr 2021 10:05:08 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: compress: remove unneed check condition

On 04/25, Chao Yu wrote:
> On 2021/4/25 8:47, Jaegeuk Kim wrote:
> > On 04/22, Chao Yu wrote:
> > > On 2021/4/22 12:04, Jaegeuk Kim wrote:
> > > > On 04/21, Chao Yu wrote:
> > > > > In only call path of __cluster_may_compress(), __f2fs_write_data_pages()
> > > > > has checked SBI_POR_DOING condition, and also cluster_may_compress()
> > > > > has checked CP_ERROR_FLAG condition, so remove redundant check condition
> > > > > in __cluster_may_compress() for cleanup.
> > > > 
> > > > I think cp_error can get any time without synchronization. Is it safe to say
> > > > it's redundant?
> > > 
> > > Yes,
> > > 
> > > But no matter how late we check cp_error, cp_error can happen after our
> > > check points, it won't cause regression if we remove cp_error check there,
> > > because for compress write, it uses OPU, it won't overwrite any existed data
> > > in device.
> > > 
> > > Seems it will be more appropriate to check cp_error in
> > > f2fs_write_compressed_pages() like we did in f2fs_write_single_data_page()
> > > rather than in __cluster_may_compress().
> > > 
> > > BTW, shouldn't we rename __cluster_may_compress() to
> > > cluster_beyond_filesize() for better readability?
> > 
> > f2fs_cluster_has_data()?
> 
> Maybe cluster_has_invalid_data()? which indicates there is invalid data
> beyond filesize.

BTW, we can compress it with zero data?

> 
> Thanks,
> 
> > 
> > > 
> > > Thanks,
> > > 
> > > > 
> > > > > 
> > > > > Signed-off-by: Chao Yu <yuchao0@...wei.com>
> > > > > ---
> > > > >    fs/f2fs/compress.c | 5 -----
> > > > >    1 file changed, 5 deletions(-)
> > > > > 
> > > > > diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
> > > > > index 3c9d797dbdd6..532c311e3a89 100644
> > > > > --- a/fs/f2fs/compress.c
> > > > > +++ b/fs/f2fs/compress.c
> > > > > @@ -906,11 +906,6 @@ static bool __cluster_may_compress(struct compress_ctx *cc)
> > > > >    		f2fs_bug_on(sbi, !page);
> > > > > -		if (unlikely(f2fs_cp_error(sbi)))
> > > > > -			return false;
> > > > > -		if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
> > > > > -			return false;
> > > > > -
> > > > >    		/* beyond EOF */
> > > > >    		if (page->index >= nr_pages)
> > > > >    			return false;
> > > > > -- 
> > > > > 2.29.2
> > > > .
> > > > 
> > .
> >