SQL Server Memory Usage Peaks to 95% and its not releasing SQL 2012

Question

We are currently running SQL 2012  64 bit, Lock Pages Enabled, 128 GB. We allocated Max Memory 112000, Min Memory to 0. We have a SQL Maintenace Job which backs up (Full Backup) of our server around 11PM at that time the SQL Server memory peaks to almost
96% even during full business hours we are constantly in the range of 56 to 60% but after 11PM within 10 minutes of the job it peaks to 95 or 96 Percentage and even after the job completes it's not releasing the memory back. I have to manually shut the sql
service and then restart at that time it comes back to normal.
Any suggestions/any help really appreciated.

Answer 1

Here are the details Memory is at 96% I still didn't restart...Please any help appreciated...The memory detals is for 24 hours  I restarted the service around 11AM before I posted my previous message..
Memory Used by SqLServer: 119329
Locked Pages Used SQLServer : 105969
Total VAS in MB : 8388607
Process Physical Memory Low : 0
Process Virtual Memory Low : 0
Max Memory set to :112000
Out of 128 Memory Last 24 hours the memory usage in %
Percent Memory Used - Total Memory is 128.0 GB
Last 24 Hours
DATE / TIME
Memory Used
19-Dec-14
11:46 PM
96.24659602
20-Dec-14
12:46 AM
96.24578349
20-Dec-14
1:46 AM
96.25146739
20-Dec-14
2:46 AM
96.24345652
20-Dec-14
3:46 AM
96.27311834
20-Dec-14
4:46 AM
96.28947067
20-Dec-14
5:46 AM
96.18931325
20-Dec-14
6:46 AM
96.09323502
20-Dec-14
7:46 AM
96.07915497
20-Dec-14
8:46 AM
96.07906977
20-Dec-14
9:46 AM
96.0784111
20-Dec-14
10:46 AM
96.07415009
20-Dec-14
11:46 AM
26.03422141
20-Dec-14
12:46 PM
33.57474359
20-Dec-14
1:46 PM
39.466561
20-Dec-14
2:46 PM
41.85940742
20-Dec-14
3:46 PM
43.89071274
20-Dec-14
4:46 PM
45.80877368
20-Dec-14
5:46 PM
46.49493281
20-Dec-14
6:46 PM
46.68486468
20-Dec-14
7:46 PM
46.69701958
20-Dec-14
8:46 PM
46.69994736
20-Dec-14
9:46 PM
57.5012455
20-Dec-14
10:46 PM
96.25695419
I verified its a sqL job and still my memory is 95%
It peaeked at 10:46PM and here are the details of the SQL job which started at 10:30 
Progress: 2014-12-20 22:30:04.39 
      Source: Check Database Integrity Task      Executing query "USE [DATASTORE]  ".: 50% complete  End Progress  Progress: 2014-12-20 22:43:06.10 
      Source: Check Database Integrity Task      Executing query "DBCC CHECKDB(N'DATASTORE')  WITH NO_INFOMSGS  ".: 100% complete  End Progress
    Progress: 2014-12-20 22:43:06.11     Source: Check Database Integrity Task      Executing query "USE [ETL_Proc]  ".: 50% complete 
 End Progress  Progress: 2014-12-20 22:46:52.56     Source: Check Database Integrity Task      Executing query "DBCC CHECKDB(N'ETL_Proc') 
  WITH NO_INFOMSGS  ".: 100% complete  End Progress  Progress: 2014-12-20 22:46:52.64     Source: Back Up Database Task
        Executing query "EXECUTE master.dbo.xp_create_subdir N'P:\SQL_Backu...".: 20% complete  End Progress  
Progress: 2014-12-20 22:46:52.64     Source: Back Up Database Task      Executing query "EXECUTE master.dbo.xp_create_subdir N'P:\SQL_Backu...".
: 40% complete  End Progress  Progress: 2014-12-20 22:46:52.64   
  Source: Back Up Database Task      Executing query "EXECUTE master.dbo.xp_create_subdir N'P:\SQL_Backu...".: 60% complete 
   End Progress  Progress: 2014-12-20 22:46:52.64     Source: Back Up Database Task    
 Executing query "EXECUTE master.dbo.xp_create_subdir N'P:\SQL_Backu...".: 80% complete  End Progress  
 Progress: 2014-12-20 22:46:52.64     Source: Back Up Database Task      
 Executing query "EXECUTE master.dbo.xp_create_subdir N'P:\SQL_Backu...".: 100% complete  End Progress 
  Progress: 2014-12-20 22:46:55.63     Source: Back Up Database Task    
    Executing query "BACKUP DATABASE [ReportServer] TO  DISK = N'P:\SQL...".: 100% complete  
End Progress  Progress: 2014-12-20 22:46:56.55     Source: Back Up Database Task    
  Executing query "BACKUP DATABASE [ReportServerTempDB] TO  DISK = N'...".: 100% complete  End Progress  Progress: 2014-12-20 22:46:57.35  
     Source: Back Up Database Task      Executing query "BACKUP DATABASE [dbamaint] TO  DISK = N'P:\SQL_Bac...".: 100% complete  End Progress 
  Progress: 2014-12-20 22:51:13.08     Source: Back Up Database Task   
     Executing query "BACKUP DATABASE [DATASTORE] TO  DISK = N'P:\SQL_Ba...".: 100% complete  End Progress
   Progress: 2014-12-20 22:51:52.72     Source: Back Up Database Task     
Executing query "BACKUP DATABASE [ETL_Proc] TO  DISK = N'P:\SQL_Bac...".: 100% complete  End Progress  Progress: 2014-12-20 22:51:54.87 
    Source: Rebuild Index Task      Executing query "USE [ReportServer]  ".: 0% complete  End Progress  Progress:
 2014-12-20 22:51:54.88     Source: Rebuild Index Task      Executing query "ALT...  The package executed successf...  The step succeeded.