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

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Message-ID: <d2b3c101-0399-4e85-5765-7b6504aaca74@huawei.com>
Date:   Sat, 31 Aug 2019 15:23:06 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <jaegeuk@...nel.org>
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 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?

Thanks,