From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 11 Apr 2002 18:16:56 +0530 (IST) From: "Amit S. Jain" Subject: Re: Memory allocation in Linux (fwd) In-Reply-To: <3CAC3E85.2040304@earthlink.net> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Joseph A Knapka Cc: linux-mm@kvack.org List-ID: Hi everyone, This is a continuation of the mail I had written earlier (see down)tellin bout my problem that when i use vmalloc()...I get an error stating "PCI bus error 2290".I think i have a slight idea what the problem could be.....Hope u all could comment on it. The large amount of memory i obtain using vmalloc is then pointed to by the skb "network" buffers as i copy data into this memory which has to be transmitted.Since the memory is discontinuous implying data is discontinuous and the ethernet card I am using is REALTEK8139 which doesnot support SCATTER/GATHER DMA.... hence the PCI bus cant find the continuous data which has to be transmitted. This is my amature fundaa....Hope u can elaborate on this... Thanks Amit < On Thu, 4 Apr 2002, Joseph A Knapka wrote: > Amit S. Jain wrote: > > > This was the message I had posted in March expecting some help from the > > Masters in Linux-mm...however there was no response...hope someone can > > respond to it now.. Pleasse.....and if u do could you please CC the > > message to my e-mail address... > > > Well, I may not be telling you anything you don't already > know, but at least here's a reply :-) > > > Hello everyone, > > I am confused about the concept of memory allocation in > > Linux and hope u all can please clear this. > > Obtaining large amount of continuous memory from the kernel is not a > > good practice and is also not possible.However,as far as non-contiguous > > memory is concerned ...cant those be obtained in huge amounts (I am talkin > > in terms of MB).Using get_free_pages or vmalloc cant large amounts of > > memory be obtained.I tried doing this but I got continuous message ssayin > > PCI bus error 2290...wass this bout???ne idea. > > > get_free_pages() allocates physically contiguous RAM of the > requested size (2^order pages). You can get lots of > non-physically-contiguous memory by calling get_free_pages() > many times with order=0. > > vmalloc() does just that, and maps the resulting pages > contiguously into kernel virtual memory. However, vmalloc() > can only map pages into kernel addresses that are not > already in use, and in a machine with lots of RAM most of the > kernel's virtual address space is occupied by 1-1 mapping > of physical RAM. So you may be running into that problem, > depending on how much RAM is in the machine. And of > course other users of vmalloc() may fragment the > kernel's virtual space and make allocation of very large > blocks impossible. > > I don't know why you would be getting "PCI bus error 2290", > sorry... > > > > Also,I will be highly obliged if you could refer a good document which can > > gimme a good explaination bout mmap function.I basically want to obtain > > zero copy from the user area straigt to the network interface without any > > copies in the kernel area. kiobuff can provide one such interface,however > > I also want to try using mmap....so please could u refer me some good > > > document. > > > (I can't comment on this.) > > Cheers, > > -- Joe > Using open-source software: free. > Pissing Bill Gates off: priceless. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/