linux-kernel - Re: [RFC Patch] mm/vmscan.c: not inherit classzone

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Date:   Fri, 14 Feb 2020 15:35:59 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, shakeelb@...gle.com,
        yang.shi@...ux.alibaba.com
Subject: Re: [RFC Patch] mm/vmscan.c: not inherit classzone_idx from previous
 reclaim

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