Comments

• OSR_Community_User-35 Member Posts: 154

  April 2000

  As you've discovered, there's a limit on the number of system PTEs used
  for mapping physical memory to system-space virtual addresses. Paged
  and nonpaged pools, plus any user buffers you lock and map, all consume
  these PTEs. So yes, there is an effective limit.
  
  There is a registry entry you can make to increase the number of system
  PTEs allocated, but there is a ceiling on how high you can increase this.
  It is entirely conceivable for you to have more physical memory than can
  be mapped into system space. When I had a NO_MORE_SYSTEM_PTEs blue-screen,
  I eventually learned that increasing the number of PTEs was not the
  solution to my problem. I had to stop mapping I/O buffers into system
  space at all, instead rearchitecting my drivers to work with MDLs.
  
  The problem can be exacerbated by odd application behavior, specifically
  using the same buffer in several outstanding I/Os. For example, imagine
  an application that does an overlapped write from the same 20 MB buffer
  to each of 16 different devices. If you map each incoming user buffer
  into system space, you've burned 320 MB worth of system PTEs (81920), well
  above the default number available (10000) or the maximum (50000). If you
  were able to recognize that it was the same buffer, you could get by with
  a single system-space mapping, consuming 5120 PTEs. If you work with
  MDLs, you don't consume any system PTEs.
  
  If you've got a driver that needs to look at or modify the data, such
  as compression or encryption, and if you are in fact the party doing
  the mapping, then you'll have to come up with some sort of throttle
  on the amount of memory you map at any given time.
  
  MmProbeAndLockPages() shouldn't consume PTEs, but MmMapLockedPages()
  does. Note that MmGetSystemAddressForMdl() can call MmMapLockedPages().
  When you're done with a mapping, be sure to call MmUnmapLockedPages().
  
  -----------------------------------------------------------------------
  Dave Cox
  Hewlett-Packard Co.
  HPSO/SSMO (Santa Barbara)
  https://ecardfile.com/id/Dave+Cox
  
  
  -----Original Message-----
  From: Kiran Mandava [mailto:[email protected]]
  Sent: Tuesday, April 11, 2000 5:41 PM
  To: NT Developers Interest List
  Subject: [ntdev] a Query!
  
  
  Hi all,
  
  Is there any limit on the total Kernel memory Usage in NT 4.0 (i am using
  the NT TaskManager to look at the total kernel memory)
  if so, could somebody pass me the info.
  
  
  thanks,
  KIRAN MANDAVA,
  Software Engineer.
  SkyStream Networks
  "Building the Broadcast Internet"
  
  
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• OSR_Community_User Member Posts: 110,217

  April 2000

  Hi all,
  
  
  What happens if i build two MDLs describing the same NonPagedPoolbuffer and
  do some operations like mmprobeandlockpages and mmunlockpages on one of the
  MDL...
  
  
  
  KIRAN MANDAVA,
  SkyStream Networks
  "Building the Broadcast Internet"

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