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Re: What is IOMalloc() Size limit for its safe use?
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Re: What is IOMalloc() Size limit for its safe use?

  • Subject: Re: What is IOMalloc() Size limit for its safe use?
  • From: Shantonu Sen <email@hidden>
  • Date: Mon, 19 May 2014 10:45:44 -0700
Where did you see that? I don’t see that in the IOKit headerdoc, and indeed that is not accurate.

IOBufferMemoryDescriptor is the best allocator to use for large amounts of anonymous memory allocated by I/O Kit drivers. It interacts the best with DMA (physical address masks), and should allocate directly from the kernel’s VM system. That does mean that it cannot re-use allocations quickly like the general purpose allocators like IOMalloc, but usually if your concern is VM or physical memory exhaustion, that’s performance is not your concern.

Shantonu

On May 19, 2014, at 3:20 AM, simran charley <email@hidden> wrote:

Thanks for reply Ed Wynne,

  I have implemented IOBufferMemoryDescriptor in my code and working fine.

but I have referred from other sources that
"IOBufferMemoryDescriptor uses IOMalloc() and IOMallocAligned() internally to allocate memory."

Does IOBufferMemoryDescriptor takes care of all limitation of IOMalloc(IOMalloc excessive use cause KP).?

Thanks




On Thu, May 15, 2014 at 9:52 PM, Ed Wynne <email@hidden> wrote:
Hi Simran,

The IOMalloc() restrictions have changed over the years, but the last time I looked (which admittedly, was a while ago) the entire IOMalloc pool was limited to something like 16MB and could not be grown. All users of IOMalloc() shared that pool and when it was out, it was out.

The best way to allocate the kinds of memory you need is with an IOBufferMemoryDescriptor. To "malloc" one you just allocate one with the flags set for the kernel only, prepare it, and then use a pointer to it's bytes. The path for "free"ing it is similar, you just complete it, and then release the object.

This method is a little slower than something like IOMalloc, but it has absolutely no restrictions outside of inherent MMU / VM limitations.

-Ed

On May 15, 2014, at 1:13 AM, simran charley <email@hidden> wrote:

Requirement:-

  1. I want to allocate memory up to ~2MB(not shared/internal use) in kernel space.

  2. This memory will get allocation/deallocation call frequently.

    I have referred following lines from book "os_x_and_ios_kernel_programming"

"Memory from IOMalloc() is intended for small and fast allocations and is not suitable for mapping into user space. Because the memory reserved for IOMalloc() comes from a small fixed-size pool, excessive use of IOMalloc() can drain this pool and panic the kernel if the pool is exhausted".

My question is:-

  1. If IOMalloc is used for small allocation then what is exact size limit for this function to use it safely?
Other limitation of IOMalloc() function for 32/64 architecture ?
Any help would be greatly appreciated!

Thanks and regards 

Simran

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References: 
 >What is IOMalloc() Size limit for its safe use? (From: simran charley <email@hidden>)
 >Re: What is IOMalloc() Size limit for its safe use? (From: simran charley <email@hidden>)

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