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What is the exact difference between MEM_RESERVE and MEM_COMMIT states?

Answer 1

+2 A:

MEM_RESERVE is allocated by the process. I.e. the address space is considered in use. However, it has not been committed. To actually use the memory for storage, it must be committed. Mark Russinovich has an excellent post, that describes all the details. From the post

Testlimit’s –r switch has it reserve virtual memory, but not actually commit it. Reserved virtual memory can’t actually store data or code, but applications sometimes use a reservation to create a large block of virtual memory and then commit it as needed to ensure that the committed memory is contiguous in the address space. When a process commits a region of virtual memory, the operating system guarantees that it can maintain all the data the process stores in the memory either in physical memory or on disk. That means that a process can run up against another limit: the commit limit.

Brian Rasmussen 2010-03-30 15:12:36

So in terms of my example, this process is reporting 'out of memory', but actually it COULD make allocations, but someone MEM_RESERVED more than they needed at that point, preventing someone else from even being able to allocate?

pj4533 2010-03-30 15:16:14

MEM_RESERVED is per process, so the process reserved that memory not someone else (as in another process).

Brian Rasmussen 2010-03-30 15:20:12

Sure, but the point being, that this process is reporting that allocations are failing, so the problem is that someone (some subsystem in THIS process) MEM_RESERVED more memory, and its preventing some other subsystem from making allocations?

pj4533 2010-03-30 15:22:30

Sorry, I got confused by the "someone" part. Anyway, it is hard to tell. As some part of the code reserved memory I would assume that it will eventually need that memory for something. Without further detail it is hard to pinpoint the source of the problem.

Brian Rasmussen 2010-03-30 15:39:25

yeah I think I got it. after loading my DMP file in debug diag, its obvious. I have like >1000 threads all stuck on EndThreadEx. Each one reserves a meg of memory, but only commits 20kb. So I just have to figure out who is making this thread that doesn't want to quit.thanks for the help!

pj4533 2010-03-30 15:49:27

Threads reserve stack space but only commit as needed (unless you're on .NET in which case they commit up front). Getting rid of some of the 1000 threads will probably be a good idea :)

Brian Rasmussen 2010-03-30 15:51:50

Answer 2

A:

Have look here. Very well explained

http://blogs.msdn.com/webtopics/archive/2010/04/02/address-summary-explained.aspx

Jas 2010-05-11 20:55:58

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What is the exact difference between MEM_RESERVE and MEM_COMMIT states?

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