On Tue, Apr 29, 2008 at 12:29 AM, 李一 <pank7yardbird@xxxxxxxxx> wrote:
thx!On Mon, Apr 28, 2008 at 10:58 PM, Rene Herman <rene.herman@xxxxxxxxxxxx> wrote:On 28-04-08 12:44, ?? wrote:Not that I'm aware of and I quite doubt anything useful exists. Are you on 32 or 64-bit? On 32-bit 1.5G is pretty large, on 64 it should be peanuts.
I got a problem here: I have a large share memory (say, 1.5GB) to be mapped into several processes' address space, I wanna make sure that the addresses those processes use to map the shared memory are a same one according to some reason. Specifically speaking, I will invoke shmat () in every process with a same second argument, a same address. But there is possibility that some times in some processes I can not make sure that the address is not in use. So my question is: what address should I choose, is there anything about process memory management in UNIX standards (posix, xopen...). I can make sure that I will attatch the shared memory right after the process starts.
My program will run on both 32 & 64 bit machines, the shared memory will be 1.5GB on 32 bit machine, and maybe 60GB on a 64 bit machine. Coz' I am managing a huge web graph, which will contain over 2 billion nodes at most, maybe it can be contained in a 64 bit machine, but I want my program to be compatible to 32 bit.
The bad thing is: I may need several such shared memory blocks, but I can only access one block at a time. What is worst, I need to randomly access the web graph, that means I need to swap between blocks.
Anyways, usually, even when not guaranteed anything, you'd expect to be able to in practice get the same address. I know recent Red Hat distributions use addressspace randomization which easily could interfere. I suppose you are using Debian:right now, my way is like this: I will occupy this huge address space at the beginning, and if it succeeded, I'll try my best not to use the mapped address space for other purposes, I wouldn't do anything while swapping, and swapping uses the same address.
sorry, I forgot to say that there are pointers in the data structures contained in the shared memory.
And, so far so good...(ugh) and I do not know if it also does. Does it?
`- Debian GNU/Linux - The power of freedom
oh, my desktop used to be Debian, but now it is Ubuntu, I take it that they are the same thing to me.
The program runs on Red Hat Distribution.
I'll do you a favour and not ask why on earth you'd want the same address.
Rene.
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--
Paul Francisco = pAnk7.yArdbird
http://pank7yardbird.googlepages.com
http://hi.baidu.com/pank7
.' ' ` . pAnk7.yArdbird ^_^
: :' : pank7yardbird(AT)gmail.com
`. ` ' liyi(AT)net.pku.edu.cn
`- Debian GNU/Linux - The power of freedom
