On Fri, Feb 28, 2020 at 05:17:00PM +0800, Aaron Lu wrote: > On Fri, Feb 28, 2020 at 03:52:59PM +0900, Joonsoo Kim wrote: > > On Fri, Feb 28, 2020 at 01:57:26PM +0800, Aaron Lu wrote: > > > On Fri, Feb 28, 2020 at 01:03:03PM +0900, Joonsoo Kim wrote: > > > > Hello, > > > > > > > > On Fri, Feb 28, 2020 at 11:23:58AM +0800, Aaron Lu wrote: > > > > > On Thu, Feb 27, 2020 at 08:48:06AM -0500, Johannes Weiner wrote: > > > > > > On Wed, Feb 26, 2020 at 07:39:42PM -0800, Andrew Morton wrote: > > > > > > > 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? > > > > > > > > > > > > Those two patches work well for some workloads (like the benchmark), > > > > > > but not for others. The full patchset makes sure both types work well. > > > > > > > > > > > > Specifically, the existing aging strategy for anon assumes that most > > > > > > anon pages allocated are hot. That's why they all start active and we > > > > > > then do second-chance with the small inactive LRU to filter out the > > > > > > few cold ones to swap out. This is true for many common workloads. > > > > > > > > > > > > The benchmark creates a larger-than-memory set of anon pages with a > > > > > > flat access profile - to the VM a flood of one-off pages. Joonsoo's > > > > > > > > > > test: swap-w-rand-mt, which is a multi thread swap write intensive > > > > > workload so there will be swap out and swap ins. > > > > > > > > > > > first two patches allow the VM to usher those pages in and out of > > > > > > > > > > Weird part is, the robot says the performance gain comes from the 1st > > > > > patch only, which adjust the ratio, not including the 2nd patch which > > > > > makes anon page starting from inactive list. > > > > > > > > > > I find the performance gain hard to explain... > > > > > > > > Let me explain the reason of the performance gain. > > > > > > > > 1st patch provides more second chance to the anonymous pages. > > > > > > By second chance, do I understand correctely this refers to pages on > > > inactive list get moved back to active list? > > > > Yes. > > > > > > > > > In swap-w-rand-mt test, memory used by all threads is greater than the > > > > amount of the system memory, but, memory used by each thread would > > > > not be much. So, although it is a rand test, there is a locality > > > > in each thread's job. More second chance helps to exploit this > > > > locality so performance could be improved. > > > > > > Does this mean there should be fewer vmstat.pswpout and vmstat.pswpin > > > with patch1 compared to vanilla? > > > > It depends on the workload. If the workload consists of anonymous > > This swap-rand-w-mt workload is anon only. Yes, I know. > > > pages only, I think, yes, pswpout/pswpin would be lower than vanilla > > I think LKP robot has captured these two metrics but the report didn't > show them, which means the number is about the same with or without > patch #1. robot showed these two metrics. See below. 50190319 ± 31% -35.7% 32291856 ± 14% proc-vmstat.pswpin 56429784 ± 21% -42.6% 32386842 ± 14% proc-vmstat.pswpout pswpin/out are improved. > > with patch #1. With large inactive list, we can easily find the > > frequently referenced page and it would result in less swap in/out. > > But with small inactive list, the pages that would be on inactive list > will stay on active list? I think the larger inactive list is mainly > used to give the anon page a chance to be promoted to active list now > that anon pages land on inactive list first, but on reclaim, I don't see > how a larger inactive list can cause fewer swap outs. Point is that larger inactive LRU helps to find hot pages and these hot pages leads to more cache hits. When a cache hit happens, no swap outs happens. But, if a cache miss happens, a new page is added to the LRU and then it causes the reclaim and swap out. > Forgive me for my curiosity and feel free to ignore my question as I > don't want to waste your time on this. Your patchset looks a worthwhile > thing to do, it's just the robot's report on patch1 seems er... I appreciate your attention. Feel free to ask. :) Thanks.
