CODEWITHSUNDEEP
c++windowsperformancememory-management64-bit
Martin Beckett
Martin Beckett

Reputation: 96197

WIn64 memory mapped files and locking pages

I need to grab large amounts (4-8Gb) of data in realtime - without dropping any data.

The old system could just about keep up with writing the data to a striped RAID array but the data has got bigger, faster than the disk have got faster (!) So I don't have time to access the disk.
The new plan is to switch to Win64, install LOTS of ram, stuff the incoming data into a buffer and then write it all at the end.

So I'm looking for:
A windows API that limits new[] to physical memory and locks pages into physical ram, or I just disable the pagefile.

Or I use memory mapped files and force a sync at the end when I close the file. Is there a memory mapped file flag that prevents a write behind until I am ready?

Upvotes: 3

Views: 2092

Answers (3)

Voo
Voo

Reputation: 30255

Instead of using plain old VirtualAlloc and locking the pages yourself, you could call VirtualAlloc with the MEM_LARGE_PAGES parameter. You need to set some settings beforehand though: See here

Large pages are by default non pageable and obviously more efficient wrt overhead. Beware that allocation times for large pages can be problematic on fragmented heaps. You may want to read this as well.

Upvotes: 1

zdan
zdan

Reputation: 29480

What you'll have to do is overload operator new and allocate and lock that memory yourself.

  1. Call VirtualAlloc to allocate your chunk of memory.
  2. Call VirtualLock to lock those pages to physical RAM. Note that it can sometimes be difficult to convince windows to do this, but will usually work if you have way more than enough RAM and you have set the process working set size appropriately using SetProcessWorkingSetSize. Note the special PROCESS_SET_QUOTA permission the user account your process is running under will need.

Upvotes: 5

bert-jan
bert-jan

Reputation: 968

One quick way would be to disable the system paging file system wide. You can create a special heap for your data, that uses physical memory only, but the new/delete stuff that takes care of memory management for small bits of data usually use the process heap. Use the HeapCreate() function from the win api. Now you must get new/delete to use that heap.

Upvotes: 0

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