linux-ext4 - Re: [PATCH 4/4] fs/ext4,jbd2: add support for passing write-hint with journal.

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Date:   Thu, 24 Jan 2019 09:50:35 +0100
From:   Jan Kara <jack@...e.cz>
To:     Kanchan Joshi <joshi.k@...sung.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-nvme@...ts.infradead.org,
        jack@...e.com, david@...morbit.com, tytso@....edu,
        prakash.v@...sung.com
Subject: Re: [PATCH 4/4] fs/ext4,jbd2: add support for passing write-hint
 with journal.

On Wed 09-01-19 21:01:01, Kanchan Joshi wrote:
> For NAND based SSDs, mixing of data with different life-time reduces
> efficiency of internal garbage-collection. During FS operations, series
> of journal updates will follow/precede series of data/meta updates, causing
> intermixing inside SSD. By passing a write-hint with journal, its write
> can be isolated from other data/meta writes, leading to endurance/performance
> benefit on SSD.
> 
> This patch introduces "j_writehint" member in JBD2 journal, using which
> Ext4 specifies write-hint (as SHORT) for journal.
> 
> Signed-off-by: Kanchan Joshi <joshi.k@...sung.com>

Thanks for the patch. It looks mostly good, just one nit below.

> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index d6c142d..3af4049 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4289,6 +4289,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  
>  	set_task_ioprio(sbi->s_journal->j_task, journal_ioprio);
>  
> +	sbi->s_journal->j_writehint = KERN_WRITE_LIFE_SHORT;
> +
>  	sbi->s_journal->j_commit_callback = ext4_journal_commit_callback;

So I'd rather have defines like:

#define EXT4_WRITE_HINT_JOURNAL KERN_WRITE_HINT_MIN

like I suggested in another email and then later we could add stuff like

#define EXT4_WRITE_HINT_BITMAP	(KERN_WRITE_HINT_MIN + 1)

etc.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR