linux-kernel - Re: [PATCH v4] mm: introduce validity check on vm dirtiness settings

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Date:   Thu, 21 Sep 2017 13:52:06 +0200
From:   Jan Kara <jack@...e.cz>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     jack@...e.cz, akpm@...ux-foundation.org, hannes@...xchg.org,
        mhocko@...e.com, vdavydov.dev@...il.com, jlayton@...hat.com,
        nborisov@...e.com, tytso@....edu, mawilcox@...rosoft.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        mcgrof@...nel.org, keescook@...omium.org, wuqixuan@...wei.com
Subject: Re: [PATCH v4] mm: introduce validity check on vm dirtiness settings

On Thu 21-09-17 21:59:52, Yafang Shao wrote:
> we can find the logic in domain_dirty_limits() that
> when dirty bg_thresh is bigger than dirty thresh,
> bg_thresh will be set as thresh * 1 / 2.
> 	if (bg_thresh >= thresh)
> 		bg_thresh = thresh / 2;
> 
> But actually we can set vm background dirtiness bigger than
> vm dirtiness successfully. This behavior may mislead us.
> We'd better do this validity check at the beginning.
> 
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

Just one nit below:

> +
> +    /* needn't do validity check if the value is not different. */
> +	if (ret == 0 && write && dirty_background_ratio != old_ratio) {

Whitespace before the comment is broken. Generally I don't think the
comment brings much so I'd just delete it.

								Honza

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