Date: Thu, 21 Sep 2017 13:52:06 +0200
From: Jan Kara <jack@suse.cz>
To: Yafang Shao <laoar.shao@gmail.com>
Cc: jack@suse.cz, akpm@linux-foundation.org, hannes@cmpxchg.org,
        mhocko@suse.com, vdavydov.dev@gmail.com, jlayton@redhat.com,
        nborisov@suse.com, tytso@mit.edu, mawilcox@microsoft.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org, mcgrof@kernel.org,
        keescook@chromium.org, wuqixuan@huawei.com
Subject: Re: [PATCH v4] mm: introduce validity check on vm dirtiness settings
Message-ID: <20170921115206.GB16731@quack2.suse.cz>
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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@gmail.com>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@suse.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@suse.com>
SUSE Labs, CR