[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20200226193942.30049da9c090b466bdc5ec23@linux-foundation.org>
Date: Wed, 26 Feb 2020 19:39:42 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: js1304@...il.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>,
Hugh Dickins <hughd@...gle.com>,
Minchan Kim <minchan@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>,
Mel Gorman <mgorman@...hsingularity.net>, kernel-team@....com,
Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 0/9] workingset protection/detection on the anonymous
LRU list
On Thu, 20 Feb 2020 14:11:44 +0900 js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> Hello,
>
> This patchset implements workingset protection and detection on
> the anonymous LRU list.
The test robot measurement got my attention!
http://lkml.kernel.org/r/20200227022905.GH6548@shao2-debian
> * Changes on v2
> - fix a critical bug that uses out of index lru list in
> workingset_refault()
> - fix a bug that reuses the rotate value for previous page
>
> * SUBJECT
> workingset protection
>
> * PROBLEM
> In current implementation, newly created or swap-in anonymous page is
> started on the active list. Growing the active list results in rebalancing
> active/inactive list so old pages on the active list are demoted to the
> inactive list. Hence, hot page on the active list isn't protected at all.
>
> Following is an example of this situation.
>
> Assume that 50 hot pages on active list and system can contain total
> 100 pages. Numbers denote the number of pages on active/inactive
> list (active | inactive). (h) stands for hot pages and (uo) stands for
> used-once pages.
>
> 1. 50 hot pages on active list
> 50(h) | 0
>
> 2. workload: 50 newly created (used-once) pages
> 50(uo) | 50(h)
>
> 3. workload: another 50 newly created (used-once) pages
> 50(uo) | 50(uo), swap-out 50(h)
>
> As we can see, hot pages are swapped-out and it would cause swap-in later.
>
> * SOLUTION
> Since this is what we want to avoid, this patchset implements workingset
> protection. Like as the file LRU list, newly created or swap-in anonymous
> page is started on the inactive list. Also, like as the file LRU list,
> if enough reference happens, the page will be promoted. This simple
> modification changes the above example as following.
One wonders why on earth we weren't doing these things in the first
place?
> * SUBJECT
> workingset detection
It sounds like the above simple aging changes provide most of the
improvement, and that the workingset changes are less beneficial and a
bit more risky/speculative?
If so, would it be best for us to concentrate on the aging changes
first, let that settle in and spread out and then turn attention to the
workingset changes?
Powered by blists - more mailing lists