My first question where are you looking for SQL Server memory consumption. Please don't use task manager or process monitor, these do not show correct value when SQL Server service account has Locked pages in memory privilege. just use below query to see memory consumed by SQL Server
from sys. dm_os_process_memory
There was notable change in SQL Server memory code in SQL Server 2012 but no where its related to what you are seeing. SQL Server memory allocation is dynamic in nature when SQL Server boots up it would grow its memory notification till the
highMemoryResourceNotification resource notification is revoked.SQL Server will keep allocating memory based on its need as long as there is memory available I.e. as long as
MEMPHYSICAL_HIGH (HighMemoryResourceNotification )notification is signaled in widows and will scale down its usage when there is
MEMPHYSICAL_LOW (LowMemoryResourceNotification) signaled in windows. When available memory is between the low memory and high memory SQL Server will try to maintain the memory usage stable
( RESOURCE_MEM_STEADY) with some exceptions.
With 48G memory you have set max server memory to 44G and only given 4 G to OS. IMO this is not correct you must give at least 6 G OS. You should give enough memory to OS so that it would have enough to allocate otherwise it would start signaling low memory notifications and SQL Server would have to trim its memory consumption.
Does SQL Server service account has Locked pages in memory privilege. If not you should give it, but before doing that please leave 6-7 G for OS( I am assuming here that this is dedicated system for SQL Server)
If you want SQL server to consume more memory create a dummy table and then start inserting large number of records in it at same time start running multiple
Select * statements you would see SQL Server memory consumption rising. If you want to check SQL Server memory consumed by SQL Server use query posted above