Messages in this thread |  | | From | "Dan Maas" <> | Subject | Re: Hi.... I guess linux-kernel.. | Date | Tue, 25 Sep 2001 07:18:12 -0400 |
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> I want to know, how use continuous memory over 128k at linux kernel... > kmalloc is 128k limit... > But, I want continous memory over 128k at linux kernel...
kmalloc() returns physically contiguous regions of memory. The 128KB limit exists because it is difficult to find a free memory block that large in a running system, due to fragmentation.
You have two options - if you can use a virtually (but not physically) contiguous region of memory, use vmalloc(). This works fine for kernel data structures. If you are using the memory as a DMA buffer however, you need to be aware that the pages are not physically contiguous, so you have to DMA each page individually (scatter/gather). Also for DMA to 32-bit PCI devices, use vmalloc_32() instead of vmalloc() (which might give you high-memory pages that are inaccessible to 32-bit devices).
The second option is to grab a large physically-contiguous region of memory at boot time. There are a few kernel patches available that provide this feature, although I haven't used them. For a really quick hack, you can use the "mem=xxxM" boot-time option to tell the kernel to use less physical memory than you actually have, and then claim the remaining memory for your own use.
Regards, Dan
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