Messages in this thread | | | From | Laurent Pinchart <> | Subject | VM_RESERVED and PG_reserved : Allocating memory for video buffers | Date | Thu, 15 Dec 2005 20:09:33 +0100 |
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Hi everybody,
I'm writing a Linux driver for a USB Video Class compliant USB device. I manage to understand pretty much everything on my own until the point where I have to allocate video buffers.
I read other drivers to understand how they proceed. Most of them used vmalloc with SetPageReserved and remap_pfn_range to map the memory to user space. I thought I understood that, when I noticed that vm_insert_page has been added in 2.6.15. I wasn't sure how to prevent pages from being swapped out, so I read the excellent "Understanding the Linux Virtual Memory Manager", but I'm still not sure to understand everything. This is where I ask for your help.
I need to allocate big buffers, so vmalloc is the way to go, as I don't need contiguous memory. I need to map those buffers to user space, and I understand that vm_insert_page will do the job nicely. My fears come from pages being swapped out. I suppose I need to prevent that, as a page fault in interrupt is a Bad Thing(TM). I'm not sure how PG_reserved and VM_RESERVED interract with eachother. Can kernel pages be swapped out if they are not mapped to user space ? Or does kswapd only walk VMAs when it tries to find pages that will be swapped out ? If the later is true, is it enough to set VM_RESERVED on the VMA in the mmap handler ?
Memory management is quite complex in the Linux kernel, and I definitely need some help to understand how all the magic is performed :-)
Best regards,
Laurent Pinchart - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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