linux-kernel - Re: [PATCH v2 0/2] Add a new scheme to support demotion on tiered memory system

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Date:   Wed, 22 Dec 2021 16:01:05 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     sj@...nel.org, ying.huang@...el.com, dave.hansen@...ux.intel.com,
        ziy@...dia.com, shy828301@...il.com,
        zhongjiang-ali@...ux.alibaba.com, xlpang@...ux.alibaba.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Add a new scheme to support demotion on tiered
 memory system

On Wed, 22 Dec 2021 19:14:39 +0800 Baolin Wang <baolin.wang@...ux.alibaba.com> wrote:

> Now on tiered memory system with different memory types, the reclaim path in
> shrink_page_list() already support demoting pages to slow memory node instead
> of discarding the pages. However, at that time the fast memory node memory
> wartermark is already tense, which will increase the memory allocation latency
> during page demotion. So a new method from user space demoting cold pages
> proactively will be more helpful.
> 
> We can rely on the DAMON in user space to help to monitor the cold memory on
> fast memory node, and demote the cold pages to slow memory node proactively to
> keep the fast memory node in a healthy state.
> 
> This patch set introduces a new scheme named DAMOS_DEMOTE to support this feature,
> and works well from my testing. Any comments are welcome. Thanks.

This is interesting.

I think it would be helpful if we could have some example scenarios in
this changelog, help people understand how to use DAMOS_DEMOTE and what
effects it has.

Documentation/admin-guide/mm/damon/usage.rst would like an update?

And the DAMON user space tool?