On Thu, 20 Feb 2020 14:11:44 +0900 js1304@xxxxxxxxx wrote: > From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > 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?
