Contiguous physical memory allocations for device drivers

The next memory allocation function that we show you is vmalloc, which allocates a contiguous memory region in the virtual address space. Although the pages are not consecutive in physical memory (each page is retrieved with a separate call to alloc_page), the .  · A driver that must use contiguous memory should allocate this memory during driver initialization because physical memory is likely to become fragmented over time as the operating system allocates and frees memory. Typically, a driver calls MmAllocateContiguousMemory from its DriverEntry routine to allocate an internal buffer for long-term use, and frees the buffer just before the driver is Header: wdm.h (include Wdm.h, Ntddk.h).  · The contiguous memory allocation (CMA) patches are an attempt to put together a flexible solution which can be used in all drivers. The basic technique will be familiar: CMA grabs a chunk of contiguous physical memory at boot time (when it's plentiful), then doles it out to drivers in response to allocation requests.

There are two ways for a device driver to allocate a contiguous buffer: The device driver can allocate a chunk of physical memory at boot-time. This is reliable because most of the physical A chunk of physical memory can be allocated on demand, but it may be difficult to find a contiguous free. Contiguous Memory Allocator (CMA) can help solve the memory fragmentation problem. Static Memory vs. CMA memory Multimedia example. CMA Memory Multimedia IP memory System memory. Size defined at boot time System uses for swap, mmap’ed files, moveable memory pages Non-multimedia operations Multimedia Multimedia IP memory System memory. operations System flushes swap, mmap’ed files, moves pages Memory becomes available for multimedia. Now, the helper driver only ask for the size to allocate in registry and allocates the memory in the driver entry, and send the adress via an IOcTL initiated by the main driver. I have still some issues: I install the driver by right-clicking on the inf file, but I can't see my device in the non pnp drivers list in the device manager.

Contiguous memory is often required for device drivers where the device uses DMA. We have done work on the physical memory allocation algorithms in the. vmalloc allocates contiguous memory in virtual memory but it doesn't guarantee that memory allocated in physical memory will be contiguous. Vmalloc is declared. Mostly hardware devices require physically contiguous memory allocations. • Any regions of memory that hardware devices work with must exist as a physically.