Re: how to reserve memory in linux?
On 10/21/06, Ming Liu [EMAIL PROTECTED] wrote: Dear sudheer,About the mem=xx argument, I checked it from the website and got such aexplanation:This argument has several purposes: The original purpose was to specify theamount of installed memory (or a value less than that if you wanted to limit the amount of memory available to linux).From the argument above, it says mem=xx is to specify the amount ofmemory available to Linux. I am not sure if I am right, but I think if Iuse such an argument, that reserved part (that 5MB you mentioned), is not available any more for Linux to access it.My original meaning is: specify a fixed physical address for a mount ofmemory for reserved use. The point is to make this part of memory fixed inthe memory of physical address, and then another I/O peripheral could use DMA to access such a fixed physical address memory. However if I don'treserve such a part, I must let Linux to allocate such a memory part. Andthen Linux will not put it in a fixed physical address yes and then theperipheral will not know where is this part. why do you think so ? Can't you give the physical address of the allocated memory from linux kernel to peripheral's DMA.? Unless you need to hardcode the physicall address i hope virt_to_phys(kmalloc_address) can be given to DMA. Sorry if i am still wrong in understanding your requirement. Am I right? Thanks for your idea.Also other ideas are appreciated. RegardsMingConsidering your setup as normal desktop, I hope this can be done bygivingmem= xxmas the boot arguments.Say the dmesg in your systemshows 495MB LOWMEM available..In the boot arguments you can give mem=490msaying the linux to use only 490MB . The rest 5MB can be used lateras youwish._享用世界上最大的电子邮件系统― MSN Hotmail。 http://www.hotmail.com___Linuxppc-embedded mailing listLinuxppc-embedded@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-embedded ___ Linuxppc-embedded mailing list Linuxppc-embedded@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-embedded
Re: how to reserve memory in linux?
Dear Rahul, why do you think so ? Can't you give the physical address of the allocated memory from linux kernel to peripheral's DMA.? Unless you need to hardcode the physicall address i hope virt_to_phys(kmalloc_address) can be given to DMA. Sorry if i am still wrong in understanding your requirement. In fact, I have considered this method before. Just to dynamically allocate such a memory buffer and then tell the peripheral its physical address for accessing. However, because I really know little about the memory management in Linux, so I am not sure if the following question could be guaranteed: Q. When I dynamically allocate a large amount of memory, I am not sure if I can allocate a physically continous large amount of memory. For the peripheral, it hopes the continous physical address, unless it has scatter-gather function. I think I must dig deeply into LDD memory management chapter to find the answer. :) Of course, I appreciate your idea and suggestion. This is really a candidate method to solve my problem. Thanks a lot. Regards Ming _ 与联机的朋友进行交流，请使用 MSN Messenger: http://messenger.msn.com/cn ___ Linuxppc-embedded mailing list Linuxppc-embedded@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-embedded
Re: how to reserve memory in linux?
Dear Eric, Have you tried the function alloc_bootmem_low() early in the boot process in main.c ? Yes, it sounds reasonable. With this function, I can reserve a large amount of buffer during booting time. But I think maybe it will be better to put this function in the device driver and when booting time, the driver is loaded and the memory part is reserved for later use, right? Actually, you can only do this at boot time before any of the standard memory setup routines run. Consult the linux device drivers book and also do some internet research on the subject to get the official documentation of this functionality. I'd rather you get the information from these sources than from me, since there is plenty of room for error when using these functions. Here's a link I found to the book: (the 2nd Edition) http://www.xml.com/ldd/chapter/book/ch07.html Thanks for your idea so much. It's really helpful. Regards Ming _ Ãâ·ÑÏÂÔØ MSN Explorer: http://explorer.msn.com/lccn _ All-in-one security and maintenance for your PC. Get a free 90-day trial! http://clk.atdmt.com/MSN/go/msnnkwlo005002msn/direct/01/?href=http://www.windowsonecare.com/?sc_cid=msn_hotmail ___ Linuxppc-embedded mailing list Linuxppc-embedded@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-embedded
