Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 14 Feb 2020 15:35:59 +0800
From:   Wei Yang <richardw.yang@linux.intel.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Wei Yang <richardw.yang@linux.intel.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, shakeelb@google.com,
        yang.shi@linux.alibaba.com
Subject: Re: [RFC Patch] mm/vmscan.c: not inherit classzone_idx from previous
 reclaim
Message-ID: <20200214073559.GA28295@richard>
Reply-To: Wei Yang <richardw.yang@linux.intel.com>
References: <20200209074145.31389-1-richardw.yang@linux.intel.com>
 <20200211104223.GL3466@techsingularity.net>
 <20200212022554.GA7855@richard>
 <20200212074333.GM3466@techsingularity.net>
 <20200214020515.GC20833@richard>
 <20200214024806.GU7778@bombadil.infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200214024806.GU7778@bombadil.infradead.org>
User-Agent: Mutt/1.9.4 (2018-02-28)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Feb 13, 2020 at 06:48:06PM -0800, Matthew Wilcox wrote:
>On Fri, Feb 14, 2020 at 10:05:15AM +0800, Wei Yang wrote:
>> On Wed, Feb 12, 2020 at 07:43:33AM +0000, Mel Gorman wrote:
>> >Broadly speaking it was driven by cases whereby kswapd either a) fell
>> >asleep prematurely and there were many stalls in direct reclaim before
>> >kswapd recovered, b) stalls in direct reclaim immediately after kswapd went
>> >to sleep or c) kswapd reclaimed for lower zones and went to sleep while
>> >parallel tasks were direct reclaiming in higher zones or higher orders.
>> 
>> Thanks for your explanation. I am trying to understand the connection between
>> those cases and the behavior of kswapd.
>> 
>> In summary, all three cases are related to direct reclaim, while happens in
>> three different timing of kswapd:
>
>Reclaim performed by kswapd is the opposite of direct reclaim.  Direct
>reclaim is reclaim initiated by a task which is trying to allocate memory.
>If a task cannot perform direct reclaim itself, it may ask kswapd to
>attempt to reclaim memory for it.

Not totally opposite, I think.

They both reclaim some memory, while after direct reclaim, some freed memory
will be allocated.

Is this the difference you want to mention?

-- 
Wei Yang
Help you, Help me