We recently ran out of memory on our sites under an Azure App Service Plan.
This threw a "Memory Resource Exhausted" error on all Apps.
Clicking "CPU Percentage and Memory Percentage" shows a spike to 82% in last 24 hours.
Navigating to "Metrics per Instance (App Service Plan)" I get a visual of all Web Apps.. Adding up ALL their Working Set in MBs added up to 22% at time of 82% App Service Plan usage.
This SO answer suggests viewing memory usage in Kudu.
Does Azure Dashboard or Kudu have any way to show a break down of specifically "App Service Plan" memory usage?
Go to Diagnose and Solve Problems in the Azure portal for your Azure Web App and choose "High Memory Usage" on the tiles on the right to see a full breakdown of memory of sites and processes running on the same app service plan. You can even drill down instance by instance in the same place.
More details on this in https://docs.microsoft.com/en-us/azure/app-service/app-service-diagnostics
Also checkout the short video referred in https://azure.microsoft.com/en-in/resources/videos/azure-friday-azure-app-service-diagnostic-and-troubleshooting-experience/
This is what you see when you click Diagnose and Solve problems -> High Memory Usage
The instance here refers to the App Service Plan itself. Just below this graph, you can see Application Percent Physical Memory Usage for instance which shows memory consumption by individual sites running on the App Service Plan
If you notice that the overall memory consumption is high but the individual sites are not consuming high memory or the memory consumption of the individual sites is not adding up, then it would mean that the rest of the memory consumption is by the system processes running on that instance. This is quite possible to witness if you are running your App on a B1 or S1 Pricing Tier which has a total of just 1.75 GB of RAM and most of the time 50 % of it might be consumed by the processes or services running for the operating system as that is just the base memory usage for Windows + other processes running on the machine.
来源：https://stackoverflow.com/questions/48291287/azure-app-service-memory-usage-where-to-see-full-breakdown