On Tue, Apr 23, 2019 at 08:30:46AM -0700, Shakeel Butt wrote: > Though this is quite late, I still want to propose a topic for > discussion during LSFMM'19 which I think will be beneficial for Linux > users in general but particularly the data center users running a > range of different workloads and want to reduce the memory cost. > > Topic: Proactive Memory Reclaim > > Motivation/Problem: Memory overcommit is most commonly used technique > to reduce the cost of memory by large infrastructure owners. However > memory overcommit can adversely impact the performance of latency > sensitive applications by triggering direct memory reclaim. Direct > reclaim is unpredictable and disastrous for latency sensitive > applications. > > Solution: Proactively reclaim memory from the system to drastically > reduce the occurrences of direct reclaim. Target cold memory to keep > the refault rate of the applications acceptable (i.e. no impact on the > performance). > > Challenges: > 1. Tracking cold memory efficiently. > 2. Lack of infrastructure to reclaim specific memory. > > Details: Existing "Idle Page Tracking" allows tracking cold memory on > a system but it becomes prohibitively expensive as the machine size > grows. Also there is no way from the user space to reclaim a specific > 'cold' page. I want to present our implementation of cold memory > tracking and reclaim. The aim is to make it more generally beneficial > to lot more users and upstream it. > Why is this not partially addressed by tuning vm.watermark_scale_factor? As for a specific cold page, why not mmap the page in question, msync(MS_SYNC) and call madvise(MADV_DONTNEED)? It may not be perfect in all cases admittedly. -- Mel Gorman SUSE Labs
