How to control the excessive use of ram by SQL Server? The database server that I am using is running 6 different SQL Server instances. It has 48 GB RAM. And one of them is consuming more than 10 GB of RAM, total consumption is 20 GB for now. The RAM consumption is growing continuously. Couple of days before it was using more than 40 GB of RAM and the server was responding very slow. The application shows the crashing problems when saving data.

So I restarted the SQL Server services. 

As soon as the services were restarted, the usage came down to 4 GB, but now it is growing.
And I am worried that it will grow up to 40 GB in 4 or 5 days and make the server slow.

Service restarting is not the good option I guess. 

I also found from different sources that we can set the maximum memory usage size for SQL Server. And am not quite sure if this will help or not. I can't test this because the server is using the production database and it would be a risk if the service stops while modifying the setting in SQL Server.

Can any one help for this problem?
That is by design.  SQL Server is supposed to use all the available memory, as it is storing more and more data in memory so that it doesn't need to go back to the disk to get the same memory over and over.

If you need to limit the amount of memory that a single SQL Server instance is using you can do this in SQL Server Management Studio by right clicking on the instance name within the Object Explorer and selecting properties.  Then select the memory tab and set the maximum amount of memory that the SQL Server will be allowed to use.  Now this isn't going to limit all aspects of SQL Server to that amount of memory.  This only controls the buffer pool and the execution plan cache.  Things like CLR, Full Text, the actual memory used by the SQL Server exe files, SQL Agent, extended stored procedures, etc. aren't controlled by this setting.  However these other things typically don't need all that much memory, it's the buffer pool and the execution plan cache which need the bulk of the memory.

If you set this setting on one instance you'll want to set it on all the instances so that they don't step on each other.