linux-kernel - Re: [PATCH v4] f2fs: add bio cache for IPU

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Message-ID: <20190901071757.GA49907@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Sun, 1 Sep 2019 00:17:57 -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 v4] f2fs: add bio cache for IPU

On 08/31, Chao Yu wrote:
> On 2019/2/19 16:15, Chao Yu wrote:
> > @@ -1976,10 +2035,13 @@ static int __write_data_page(struct page *page, bool *submitted,
> >  	}
> >  
> >  	unlock_page(page);
> > -	if (!S_ISDIR(inode->i_mode) && !IS_NOQUOTA(inode))
> > +	if (!S_ISDIR(inode->i_mode) && !IS_NOQUOTA(inode)) {
> > +		f2fs_submit_ipu_bio(sbi, bio, page);
> >  		f2fs_balance_fs(sbi, need_balance_fs);
> > +	}
> 
> Above bio submission was added to avoid below deadlock:
> 
> - __write_data_page
>  - f2fs_do_write_data_page
>   - set_page_writeback        ---- set writeback flag
>   - f2fs_inplace_write_data
>  - f2fs_balance_fs
>   - f2fs_gc
>    - do_garbage_collect
>     - gc_data_segment
>      - move_data_page
>       - f2fs_wait_on_page_writeback
>        - wait_on_page_writeback  --- wait writeback
> 
> However, it breaks the merge of IPU IOs, to solve this issue, it looks we need
> to add global bio cache for such IPU merge case, then later
> f2fs_wait_on_page_writeback can check whether writebacked page is cached or not,
> and do the submission if necessary.
> 
> Jaegeuk, any thoughts?

How about calling f2fs_submit_ipu_bio() when we need to do GC in the same
context?

> 
> Thanks,