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Date:   Sat, 12 Nov 2022 09:23:41 -0500
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Hongchen Zhang <zhanghongchen@loongson.cn>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Hugh Dickins <hughd@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, kernel-team@fb.com,
        Yosry Ahmed <yosryahmed@google.com>
Subject: Re: [PATCH] mm: vmscan: fix extreme overreclaim and swap floods
Message-ID: <Y2+sbbirX11Vo+XM@cmpxchg.org>
References: <20220802162811.39216-1-hannes@cmpxchg.org>
 <17f04d65-020e-a52d-41e8-0d540e32b475@loongson.cn>
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In-Reply-To: <17f04d65-020e-a52d-41e8-0d540e32b475@loongson.cn>
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On Tue, Sep 20, 2022 at 02:12:17PM +0800, Hongchen Zhang wrote:
> On 2022/8/3 am 12:28, Johannes Weiner wrote:
> > @@ -2988,8 +2988,6 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
> >   		nr_scanned = targets[lru] - nr[lru];
> >   		nr[lru] = targets[lru] * (100 - percentage) / 100;
> >   		nr[lru] -= min(nr[lru], nr_scanned);
> We should not just remove the following line because kswapd may also call
> this function and there is no side effect to do scan adjust for kswapd,so it
> may be better to change like this:
> +    if (current_is_kswapd())
> 		scan_adjusted = true;
> > -
> > -		scan_adjusted = true

There is no scan_adjusted after this patch.

If you're saying that kswapd should set proportional_reclaim
unconditionally, then no, it should not. Proportional reclaim is not
safe at lower priority levels, as the changelog outlines in detail.