General :: Virtual Address To Physical Memory Access ?
Feb 21, 2010
A process is trying one access to memory, for example through an array (ex.: vect[0]=123. What happens?
Here below what I guess but I'm not sure and accept any comment (please, distinguish between "the system" and "the CPU" in case).
Let's suppose swapping to disk disbled.
We have two scenarios: without and with cache.
If no cache is present in the system:
1. The CPU must discover the phys addr of vect[0] virtual addr. To do that, has to read from 3 (or 2 depending on the system?) pages tables, stored in memory as well.
2. The CPU writes to the final address.
These mean 4 memory accesses.
If cache is present:
1. Like above but, if the pages tables are in cache, we have 3 accesses to that.
2. If the req. page is not in cache, it's reads from ram and transferred to it. Afterwards, cache is written.
In the best case we have 4 cache accesses.
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Apr 13, 2010
How can I get the physical address corresponding to a virtual address in linux by using /proc file system
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Nov 4, 2010
As i undertsand - out of 1GB of the virtual Address space for Kernel from 3GB to 4GB of the process address space, Kernel image (code, data, bss, stack, heap) resides staring @0x0 address. Vmalloc area starts either at the end of Physical ram size or at 896M. This 896M cap is mandated to ensure that minimum of 128MB is reserved as vmalloc_reserve for vmalloc,kmap etc.
Is the understanding correct? Now trying to map Physical Zones into this 1GB address space
Initial 16MB is mapped to ZONE_DMA
16MB - 896MB is mapped to ZONE_NORMAL
896MB - 1024MB is mapped to ZONE_HIGHMEM
Does this mean that Kernel image is residing in ZONE_DMA area? Any call to vmalloc() in kernel code will return address beyond 896M? insmod of any LKM will internally invoke vmalloc() to obtain contiguous area - where will this code physically located along with rest of kernel code in ZONE_DMA or in ZONE_HIGHMEM?
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Dec 17, 2008
When I try to access at physical address (0xD0000), we known that it is necessary to convert physical address to virtual address using function IOREMAP(0xD0000, 1024) and return me 0xC00D0000.
Now our doubt is when I have a board with I/O in address 0x150, is it necessary to convert this address to other virtual address??? or with inb(0x150) return me state of I/O in this address? How can I known where is this I/O address in my map memory?
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Jun 26, 2010
I have a 32 bit Ubuntu installed and my Laptop has 4GB RAM, but only 3GB is considered by Linux. My question is: what is the reason for the upper limit on physical memory ?
Code:
dmesg | grep Memory [0.000000] Memory: 3052428k/3112960k available (4673k kernel code, 56364k reserved, 2121k data, 656k init, 2200904k highmem) I am familiar with the virtual memory concept where linux splits upper 1GB for kernel and lower 3GB for user processes. In total, linux 32bit can address 4GB virtual addresses. Does this meant that 1GB of physical memory is already mapped to 1GB of kernel space and Linux only shows the remaining 3GB physical memory left for the user in the above command.
I did some searching on the internet and found some articles related to this, but it only confused me further since some articles suggest 4GB is the upper limit with mentioning whether it's virtual or physical memory, some bring in the concept of PAE, etc. I'm relative new to Linux's memory management, so it'd be really helpful if someone could answer this.
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Apr 20, 2010
I am using malloc and frees a lot in my program. It shows its allocated but when i remove it doesnt show as the memory is removed(I am using the top command to view VIRT memory usage). If this continously grows what would happen to my program (Will it go out of memory?)
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Apr 6, 2011
I need a small shell based program that prints the mac address of physical ethernet adapter from it's firmware. I need this utility for license generation and appliance activation. I have tried several example but none of them is flawless, The easiest method I have found is to parse the output of "ifconfig" command but it has also some drawbacks.
1. Firstly program should differentiate between physical and virtual adapters. Physical means installed on board(wired or wireless) or installed additionally. Virtual adapters are those created by VPN or created by virtualization apps such as VirtualBox/VMWare etc. I am not interested in virtual ones.
2. In case of more them one physical adapters(wired and wireless), it should print the mac address and description(name & vendor) of both/all adapters.
3. If media is disconnected then also it should be able to read the mac address and description(name, vendor) of card.
4. This one is bit complex. I know that 'ethtool' can show you the universal mac address but it's limited to use only 2 types of drivers and won't work in all cases.
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Nov 18, 2009
I want to translate the virtual address to physical address in linux C application, how to do that?
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Jul 15, 2010
I am interested to know memory layout in linux os.What are the differences between physical address and virtual address?
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Oct 22, 2009
I allocated a chunk of memory using kmalloc in a Device Driver. Kmalloc provides a pointer to the allocated memory. This is one of my first few drivers.
I assume that the address returned is a Virtual address. I need to find the physical address of the memory location. I am working on an Intel 64 bit Fedora machine. I used the virt_to_phys() routine present in <asm/io_64.h>. I found that this routine returns an unsigned long value (32 bit) instead of an unsigned long long value (64 bit). Moreover, it seems that it simply returns the address - OFFSET instead of extracting the value in the page tables.
So is there any function / system call in Linux which will allow me to see the actual physical address on the Intel 64 arch.
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Jul 19, 2010
im REALLY new with linux and ive downloaded and installed Ubuntu...now heres the question.how do i set up WLAN internet use? ive tried using ipconfig/all on windows command but im not sure which info to use where save for the Physical Address going towards the MAC Address info
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May 18, 2010
I am trying to build and bring-up Linux (embedded) for a piece of hardware which have MIPS 74K proccessor 16MB Flash, 128MB DDR and network/usb support. How to configure/set into the kernel the exact addresses of the physical memory map? How does the kernel know where is the system ram, i/o memory, root FS? I have read some book and I found how the applications can go and read some special files like /proc/iomem to find out info about memory but what I need is how to set those addresses at the beginning when I build the kernel and FS in order to boot the kernel on my h/w.
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Jan 11, 2010
let me know how to clear cache memory ( RHEL 5.1 ) as it consumes almost 100% physical memory.
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Oct 20, 2010
I am monitoring physical memory in a server I administer, and my hardware provider told me they had increased physical memory size to 4Gb... However, using several tools (free -m; top; dmesg | grep Memory; grep MemTotal /proc/meminfo I discovered that I actually have 3Gb, not 4... But, my doubt comes from the fact that dmesg | grem Memory tells me I have 3103396k/4194304k available The first number is effectively 3Gb, but the second one, is 4! so, why I am looking at this two different numbers?
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Jul 11, 2011
Kernel 2.6.21.5, slackware 12.0
nasm 2.03.01
ld 2.17
GNU gdb 6.6
This GDB was configured as "i486-slackware-linux".
Code:
What could the cause of the message output by gdb possibly be? Reading some tutorials, I've learn the flat memory model is used in linux. So, in particular, I needn't care about the DS segment register.
Also, line 7 in the listing above, suggests nasm is assuming 32-bit addressing and so, I think it is using the flat memory model.
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Sep 12, 2010
When we want to setup a linux system, there is a common a suggestion like set the swap space as twice as big than your physical memory, I want to know why do we need this and how is this suggestion come from?
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Sep 3, 2010
I am doing a test to get the memory used by apache`s apache2 processes. I used a script to get VmSize and VmRss from /proc/pid/status, and loop through that to get the sum of VmSize and VmRss of all the apache2 processes.
I found the VmSize (about 4GB) and VmRss (about 3.4GB) are much larger than the physical memory (1GB) when apache server was saturated. It was said because of the multi-counted libiraries size used by many processes simultaneously. Then , how to get the physical memory used by apache2 processes? Or how to get a more reasonable memory data?
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May 17, 2010
One of the tasks I want to do is to read/write from/to any physical address. My question is how do I get a physical address on my Linux desktop. I was thinking of using some utility to dump my BIOS settings, and modify a "not so important" memory address there? Is this possible. Otherwise is there any other physical address I can read/write
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Feb 3, 2010
we found that if we use 'top' to show the memory usage of a server (SuSe Linux 10), we can get virtual memory usage as well as 'Resident memory' usage. For virtual mem or a particular process, it is around 1.1GB, which is large but for resident memory, it only consumes 300MB. Are there anyone who knows what the differences are? I would also like to know whether the difference (1.1GB - 300MB) = 800MB are actually available for use by other applications in the system.
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Jul 30, 2010
I need to deploy Windows Server 2008 R2 onto a server that is currently running Linux. Effectively, I want to restore a Windows disk image onto the Linux system hard disk.I don't have physical access to the machine, so I need to find a way to do everything remotely, using SSH (no KVM). And the Linux machine only has one hard disk - the one containing the OS. However, I might be able to create a partition in free space at the end of the hard disk to store the image (I might need some help with the Linux commands). Or perhaps the image file can be pulled via FTP.
I tried Acronis but was disappointed to find that it doesn't seem to allow me to overwrite the system partition (unlike the Windows version of Acronis, which is capable of doing this with a restart).
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Jun 9, 2011
We want to set up a Linux server (hosting Git or later SVN repositories) which should have all stored data strongly encrypted, so that if one steals the server the data cannot be read. For example, our notebooks have all important data stored on a "true-crypted" partition.
We plan to access it with SSH private keys and only after successful login should the data be readable. The server would be located in our office, shut down at night and not be connected to the Internet directly, but only accessible in our intranet.
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Jun 23, 2011
I have rented a server in a datawarehouse to host my mysql databases, subversion repositories, websites etc. I don't have physical access to this server (I don't even know the location of the data warehouse).
I connect over SSH (Putty) to this server.
When I login I get the message that new release "natty" is available (1104). Run "do-release-upgrade" to upgrade to it. I've never done an upgrade, so I'm afraid there has to be a reset during the upgrade process and a manual action on the machine itself to restart it.
Is it possible to do this upgrade without manual intervention, can somebody give me perhaps a pointer to a location of a good "howto"
For good understanding: I don't have a graphical user interface, just the command line through Putty. I've installed the utility "screen",
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Jan 23, 2011
I'd like to ask you how install new physical memory in my hp ml350 g6 server with linux redhat operating system>
i sugess it is easy like in windows operating system but there is frind told me you must make mount , i am new with linux os .
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Nov 22, 2009
I am writing an application that wants to access periphals registers outside the standard (allowed) memory area.
Doing so gets me "segmentation fault".
I know, this is natural behaviour.
One way of getting around this is writing the module which has to be loaded by linux. I will consider this some time later.
For now, I want to come to some quick result and allow linux or gcc compiler to write to those memory areas of periphals. Is there a direct way to do so?
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Feb 21, 2011
if i attach a shared memory to my process whch part of the address space it will add(like stack, heap, data, code...).
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Aug 30, 2010
I got the VMrss used by a process as about 2GB, but the physical memory of my computer is only 1G.
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Oct 24, 2010
I have a system with 2G of memory and swap memory of 4G.
This is the output from :
PHP Code:
How could they do to the memory cache to be used as much? Because, occasionally, swap is used and note that the system could use the memory cache does not swap ...
Slackware current 64 multilib.
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Dec 9, 2010
I am running a series of tests for an implementation of a remote pager that sends page faults to other computers in a network. Long story short, I was wondering if there is an easy way to force a process to use virtual memory as oppose to physical RAM so that I can better measure the performance of my implementation against how the system would perform while swapping to the hard drive.
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Aug 27, 2010
I have rhgel5.3 installed on IBM blade server having 16 GB of physical memory. But it showing only 4GB.
#cat /proc/meminfo
#free -m
#top
[code]...
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Jun 20, 2010
Why linux uses swap space, even if there are free physical memory available.
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