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32-bit Virtual Memory Constraints in Windows 2000 and 2003

32-bit Virtual Memory Constraints in Windows 2000 and 2003. Mark Friedman Demand Technology 1020 Eighth Avenue South, Suite 6, Naples, FL 34102 USA phone: (239) 261-8945 fax: (239) 261-5456 e-mail: markf@demandtech.com http://www.demandtech.com. Outline. Topics Virtual Memory concepts

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32-bit Virtual Memory Constraints in Windows 2000 and 2003

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  1. 32-bit Virtual Memory Constraints in Windows 2000 and 2003 Mark Friedman Demand Technology 1020 Eighth Avenue South, Suite 6, Naples, FL 34102 USA phone: (239) 261-8945 fax: (239) 261-5456 e-mail: markf@demandtech.com http://www.demandtech.com

  2. Outline • Topics • Virtual Memory concepts • Virtual Memory constraints in 32-bit Windows • Physical Address Extension (PAE) • Leaking processes • Page faults/sec

  3. Virtual Memory Manager • 4 GB virtual per process address space • Lower 2 GB - Private • Page 0 reserved • Code pages • Heap • Upper 2 GB - System • System code • Shared dlls • System cache

  4. Virtual Memory Manager • All address spaces share the virtual addresses from the same upper 2 GB of the System area • All virtual addresses in the lower 2 GB User area are unique • Shared memory in the System range can be used for IPC

  5. Virtual Memory Manager • Commit Limit • Limit on the number of Virtual Memory pages that the system will allocate • Sizeof (RAM) + paging file(s) • Memory allocations start to fail as % Committed Bytes in Use 100%

  6. Virtual Memory Manager • Commit Limit • But page files are extendible! • Should you or shouldn’t you?

  7. Virtual Memory Manager

  8. Extended Virtual Addressing • Boot.ini /3 GB switch • Virtual storage constraint relief for some applications • Squeezes the System VM into 1 GB • Physical Address Extension (PAE) • Supports 36-bit real addresses on Xeon processors • Address Windowing Extensions (AWE) • Permits processes to address real memory > 4 GB

  9. Virtual Memory Manager • Boot.ini /3 GB switch • Virtual storage constraint relief for some server applications • SQL Server • Exchange 2000 • Etc. • /userva=SizeInMB subparameter, where SizeinMB can be any value between 2048 and 3072

  10. Physical Address Extension • PAE is supported on most recent Intel servers • Physical addresses are 36-bits • Up to 64 GB of RAM can be installed • Page Table Entries (PTEs) remain 32-bits • Process address spaces are still limited to 4 GB. How can they exploit 64 GB of RAM? • Expand sideways, using multiple address spaces • Large Memory Enabled (LME) device drivers • Address Windowing Extensions (AWE) • Boot.ini /pae switch • Limitation: system addresses can be no higher than 16 GB

  11. 16 GB 4 GB SQL Server 4 GB SQL Server 4 GB SQL Server Physical Address Extension • Expand sideways, using multiple address spaces • e.g., MS SQL Server

  12. Address Windowing Extensions (AWE) • API that allows processes to address real memory locations outside their 4 GB virtual addressing range • Create and manage memory Overlays • Used in conjunction with PAE AllocateUserPhysicalPages Virtual Alloc MapUserPhysicalPages

  13. AWE Note: Frequent unmapping and remapping of Physical Memory blocks is expensive!

  14. AWE support • MS Exchange: /3 GB support only • MS SQL Server 2000: /3 GB, PAE, & AWE • Multiple process instances • awe enabled = 1 • Also Set max server Oraclememory • Oracle: /3 GB, PAE, & AWE • AWE_WINDOW_MEMORY • SAS: /3 GB, PAE • Work library can be placed in PAE memory

  15. Win64 Virtual Memory

  16. Virtual Memory Manager • Real Memory allocation Counters • Available Bytes • Pool non-paged Bytes, • Pool Paged Resident Bytes, • System Cache Resident Bytes, • System Code Resident Bytes, • System Driver Resident Bytes • Instantaneous Counters (all reported as Bytes) • Trimmed Pages on the Modified List are not counted (assumed to be small) • Cache Bytes is actually the (pageable) System Working Set = Pool Paged Resident Bytes + System Cache Resident Bytes + System Code Resident Bytes + System Driver Resident Bytes

  17. Real Memory allocation Counters

  18. Virtual Memory Manager • Memory allocation Counters • Available Bytes • Available KBytes • Available MBytes • Pool non-paged Bytes, • Pool Paged Resident Bytes, • System Cache Resident Bytes, • System Code Resident Bytes, • System Driver Resident Bytes

  19. What is the differencebetween Pool Paged Bytes and Pool Nonpaged Bytes? • Which applications would use which VM pool?

  20. Virtual Memory map

  21. Virtual Memory map • Paged • Memory mapped files • Shared DLLs • File Server • IIS (html, jpg, gif) • Page tables • nonPaged: • I/O buffers used by device drivers • TCP Session data • Kernel threads (win32k.sys per process)

  22. Virtual Memory map (Win2K) • Virtual memory map features overflow areas for the file cache, PTEs, and Paged/nonPaged Pools • One reserved area of virtual memory can fill up faster than the others; • No hard limits on the sizes of the pools

  23. Virtual Memory map (Win2K) • No hard limits on the sizes of the pools • One reserved area of virtual memory can fill up faster than the others;

  24. Virtual Memory map (Win2003) • Virtual memory map is dynamic, subject to adjustment by the OS • One reserved area of virtual memory can fill up faster than the others • When any one area fills, VMM routines can empty the file cache to acquire more vm for the paged/nonpaged pools Paged Pool Cache PTEs nonPaged Pool

  25. Nonpaged pool size (ref. Q126402): • Obsolete in Windows 2003 • Dynamic adjustment of system virtual memory when one pool is exhausted. • NonPagedPoolSize, NonPagedPoolSize, and SystemPagescan also be set explicitly. • But how can you tell when you are running out of space in one of these pools?

  26. Default Paged and Nonpaged pool size can be overridden:

  27. Default Paged and Nonpaged pool size can be overridden (Win 2003): • System Pages = x’ffff ffff’16 or -1 • Maximizes the number of PTEs that can be built • Potentially useful with /PAE or Terminal Services • PagedPoolSize = x’ffff ffff’16 or -1 • Allows the OS maximum flexibility to determine the size of the Paged Pool • Or PagedPoolSize and NonPagedPoolSize can be set explicitly • LargeSystemCache controls the maximum virtual address range of the file cache • 512 MB – 1 GB

  28. !vm Debugger command runs the Page Frame Number (PFN) database Available Pages: 4920 ( 19680 Kb) ResAvail Pages: 358 ( 1432 Kb) Locked IO Pages: 251 ( 1004 Kb) Free System PTEs: 204387 ( 817548 Kb) Free NP PTEs: 28645 ( 114580 Kb) Free Special NP: 0 ( 0 Kb) Modified Pages: 596 ( 2384 Kb) Modified PF Pages: 660 ( 2640 Kb) NonPagedPool Usage: 2750 ( 11000 Kb) NonPagedPool Max: 33768 ( 135072 Kb) PagedPool 0 Usage: 3544 ( 14176 Kb) PagedPool 1 Usage: 1359 ( 5436 Kb) PagedPool 2 Usage: 1340 ( 5360 Kb) PagedPool Usage: 6243 ( 24972 Kb) PagedPool Maximum: 138240 ( 552960 Kb) Shared Commit: 6842 ( 27368 Kb) Special Pool: 0 ( 0 Kb) Shared Process: 3688 ( 14752 Kb) PagedPool Commit: 6398 ( 25592 Kb) Driver Commit: 1630 ( 6520 Kb) Committed pages: 211846 ( 847384 Kb) Commit limit: 320257 ( 1281028 Kb)

  29. !poolused Debugger command accounts for all system pool allocations (plus pooltags.txt documentation) lkd> !poolused 2 Sorting by NonPaged Pool Consumed Pool Used: NonPaged Paged Tag Allocs Used Allocs Used LSwi 1 2576384 0 0 NV 287 1379120 14 55272 File 2983 504920 0 0 MmCm 16 435248 0 0 LSwr 128 406528 0 0 Devi 267 377472 0 0 Thre 452 296512 0 0 PcNw 12 278880 0 0 Irp 669 222304 0 0

  30. Poolmon utility (from DDK)

  31. Virtual Memory constraints • Virtual Memory constraints in 32-bit Windows tend to appear when sizeof (RAM)  4 GB • 2 GB private area is not enough virtual memory for some applications • e.g., SQL Server, Exchange database (store.exe) • Due to fragmentation, it is typically not possible to allocate all 2 GB • 2 GB system area is not enough virtual memory for some applications • File cache for a conventional IIS-managed web site with many static .htm, jpg, gif, etc., files to retrieve

  32. Virtual Memory constraints • Virtual Memory constraints in 32-bit Windows tend to appear when sizeof (RAM)  4 GB • Ample RAM exists, but it is not possible for your applications to access it due to virtual memory addressing limitations • Large number of Available Bytes

  33. Virtual Memory constraints • So try the /3 GB switch • 1 GB system area is not enough virtual memory for some applications • Possible shortage of Free System Page Table Entries • Possible shortage of Nonpaged Pool • Where Session data from TCP connections is stored • Due to fragmentation, it may not be possible to failover a 2 GB+ private address space (e.g., SQL Server, MS Exchange database – store.exe) using Microsoft Cluster Server (MCS) • During address space recovery on the standby node, the entire virtual memory allocation is acquired at one time

  34. Virtual Memory constraints • So try the /3 GB switch • 1 GB system area is not enough virtual memory for some applications • PagedPoolSize and NonPagedPoolSize defaults are cut in ½ • Possible shortage of Free System Page Table Entries • Possible shortage of Nonpaged Pool • Where Session data from TCP connections is stored • Where kernel threads are created per process for calls to win32k.sys (especially impacts large Terminal Server environments)

  35. Exchange 2000 memory tuning • Exchange default memory allocation parameters are “self-tuning,” but may not be optimal on servers with > 1 GB RAM • Adjust HKLM\SYSTEM\CurrentControlSet\Services\SMTPSVC\Queuing • MsgHandleThreshold & MsgHandleAsyncThreshold HKLM\SYSTEM\CurrentControlSet\Services\Inetinfo\Parameters • FileCacheMaxHandles

  36. Exchange 2000 memory tuning • Store DB cache • Store cache normally expands to fill RAM • But, maximum cache = 900 MB • This value can be adjusted using ADSI Edit tool: • msExchESEParamCacheSizeMax • msExchESEParamCacheSizeMin • Also, consider adjusting msExchESEParamLogBuffers attribute for active, back-end servers

  37. Detecting memory leaks • Processes that allocate virtual memory, but later “forget” to free it. • MS says leaks won’t happen in .Net managed code due to automatic garbage collection • But, meanwhile…, • Where to look depends on whether process or system addresses are being allocated: • Per Process: Virtual Bytes, Private Bytes, Pool Paged Bytes, Handle Count • System level: Memory Pool Paged Bytes, Pool Nonpaged Bytes and the Objects Object

  38. Detecting memory leaks • Look for a steady increase or a sharp spike in process Virtual Bytes, or the System’s Pool Paged Bytes. • If RAM is not full, the leak may also be manifest in the Memory allocation counters and result in increased paging, if RAM fills up. • For example:

  39. Detecting memory leaks (1)

  40. Detecting memory leaks (2)

  41. Detecting memory leaks (2)

  42. Detecting memory leaks (2)

  43. Detecting memory leaks (2)

  44. Detecting memory leaks (2)

  45. Detecting memory leaks (2)

  46. Detecting memory leaks (2)

  47. Detecting memory leaks (2)

  48. Lab exercise. • Open SUPPORT.200205080300.EXCHG2K.sum.smf,SUPPORT.200205090300.EXCHG2K.sum.smf, andSUPPORT.200205100300.EXCHG2K.sum.smf and investigate virtual memory usage. • Can you find the application that is leaking?

  49. Detecting Memory Leaks (3)

  50. Detecting Memory Leaks (3)

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