April 2011 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Re: Missing 1GB RAM, where is it? - SUMMARY
by Andrzej Kardas April 18, 2011

April 18, 2011

On 14.04.2011 19:30, Wick wrote: > Hi, Andrzej Kardas: > > You're very close now. I think i got it now :) > To ensure that kernel detected your 4GB RAM, we need to check the stats: > wick:~$ dmesg | grep Memory > [ 0.000000] Memory: 3716784k/4718592k available (5940k kernel code, > 787332k absent, 214476k reserved, 5017k data, 956k init) in my case: dmesg | grep Memory [ 0.000000] Memory: 3013732k/3136000k available (4692k kernel code, 120780k reserved, 2213k data, 576k init, 2224648k highmem) after few hours of digging this topic i think this amount of RAM is correct, as almost everybody from this list suggested :). Here are results of my investigation: At early start, when kernel boots and still working in real mode, actual memory map is taken from BIOS with use interruptINT 15h, AX=E820h. Result of this interrupt is dumped into ring buffer, so we can read this by dmsg. In my case: [ 0.000000] BIOS-provided physical RAM map: [ 0.000000] BIOS-e820: 0000000000000000 - 000000000009f800 (usable) [ 0.000000] BIOS-e820: 000000000009f800 - 00000000000a0000 (reserved) [ 0.000000] BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved) [ 0.000000] BIOS-e820: 0000000000100000 - 00000000bf680000 (usable) [ 0.000000] BIOS-e820: 00000000bf680000 - 00000000bf700000 (ACPI NVS) [ 0.000000] BIOS-e820: 00000000bf700000 - 00000000c0000000 (reserved) [ 0.000000] BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved) [ 0.000000] BIOS-e820: 00000000fec00000 - 00000000fec10000 (reserved) [ 0.000000] BIOS-e820: 00000000fed00000 - 00000000fed00400 (reserved) [ 0.000000] BIOS-e820: 00000000fed14000 - 00000000fed1a000 (reserved) [ 0.000000] BIOS-e820: 00000000fed1c000 - 00000000fed90000 (reserved) [ 0.000000] BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved) [ 0.000000] BIOS-e820: 00000000ff000000 - 0000000100000000 (reserved) As we can see there are still 'holes' in addresses, similar to /proc/iomem. These holes are result of INT 15h, AX=E820h, this call return map of memory but with some limitations http://www.uruk.org/orig-grub/mem64mb.html) * 1.* The BIOS will return address ranges describing base board memory and ISA or PCI memory that is contiguous with that baseboard memory.* 2.* The BIOS WILL NOT return a range description for the memory mapping of PCI devices, ISA Option ROM's, and ISA plug & play cards. This is because the OS has mechanisms available to detect them.* 3.* The BIOS will return chipset defined address holes that are not being used by devices as reserved.* 4.* Address ranges defined for base board memory mapped I/O devices (for example APICs) will be returned as reserved.* 5.* All occurrences of the system BIOS will be mapped as reserved. This includes the area below 1 MB, at 16 MB (if present) and at end of the address space (4 gig).* 6.* Standard PC address ranges will not be reported. Example video memory at A0000 to BFFFF physical will not be described by this function. The range from E0000 to EFFFF is base board specific and will be reported as suits the bas board.* 7.* All of lower memory is reported as normal memory. It is OS's responsibility to handle standard RAM locations reserved for specific uses, for example: the interrupt vector table(0:0) and the BIOS data area(40:0). So thats why there is a hole for example: 00000000000a0000 - 00000000000e0000 (point 6. Standard PC address range for VGA) and 00000000c0000000 -00000000e0000000 (point 2. mapped PCI devices). The main goal for OS is _NOT_ use memory ranges _NOT_ reported (holes) and reported memory ranges different than usable. When it comes about so many RAM unavailable, about 1 GB in my case, the answer is in documentation (http://www.intel.com/design/mobile/datashts/309219.htm) of my northbridge chipset: and@lpt:~$ lspci 00:00.0 Host bridge: Intel Corporation Mobile 945GM/PM/GMS, 943/940GML and 945GT Express Memory Controller Hub (rev 03) It is not very sophisticated unit, because it is not able to remap memory from PCI range above 4 GB region. According to documentation: "Addressing of memory ranges larger than 4 GB is _NOT_ supported." So even my CPU is supporting 36bit physical addresses and PAE, memory controller is not able to remap memory from PCI range above 4GB range as other, more advanced chipset do with help of PAE. I've also found: "The (G)MCH does not remap APIC or any other memory spaces above TOLUD (Top of Low Usable DRAM). The TOLUD register is set to the appropriate value by BIOS." So each access to memory above TOLUD is transfered to Southbridge or PCI express (which is directly connected to northbridge) or to the internal graphics device, TOLUD in my OS is 0xbf67ffffh = 3211263999 bytes, everything above it is unavailable for usage as RAM. >> On 14.04.2011 17:09, Adrian Cornish wrote: >> >> Just a thought - lower end graphic cards use system RAM as their own >> dont they Yes, in my case internal graphic controller's RAM is situated above TOLUD: and@lpt:~$ lspci -v -s 00:02.0 | grep Memory Memory at f0000000 (32-bit, non-prefetchable) [size=512K] Memory at d0000000 (32-bit, prefetchable) [size=256M] Memory at f0300000 (32-bit, non-prefetchable) [size=256K] On 14.04.2011 19:30, Wick wrote: > And about the memory hole in the /proc/iomem, I think it's related to > kernel's resource management. Dig it in kernel source codes :) Now i can say :) that, this regions (holes) are simply not available for system because they are above TOLUD and additionally not assigned to any device because I haven't particular device in PC for example bluetooth: I have space for it, but in my version of notebook was not available in standard equipment. Many thanks everybody for suggestions and help with this, now I can assume that total RAM in my PC is correct. I also learned that documentation is standard point that I should aways start digging, it can save some time:) -- regards Andrzej Kardas http://www.linux.mynotes.pl

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FW: Kernelnewbies Digest, Vol 5, Issue 20
by ashutosh mishra April 18, 2011

April 18, 2011

>hi all.. >i have been working on char device driver. >i need a good document on advance char device driver..? > From: kernelnewbies-request(a)kernelnewbies.org > Subject: Kernelnewbies Digest, Vol 5, Issue 20 > To: kernelnewbies(a)kernelnewbies.org > Date: Thu, 14 Apr 2011 12:00:01 -0400 > > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. Re: Missing 1GB RAM, where is it? (Andrzej Kardas) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 14 Apr 2011 17:43:05 +0200 > From: Andrzej Kardas <andrzej-kardas(a)o2.pl> > Subject: Re: Missing 1GB RAM, where is it? > To: Adrian Cornish <adrianc(a)cqg.com> > Cc: kernelnewbies(a)kernelnewbies.org > Message-ID: <4DA71609.5070800(a)o2.pl> > Content-Type: text/plain; charset="iso-8859-1" > > > > On 14.04.2011 17:09, Adrian Cornish wrote: > > Just a thought - lower end graphic cards use system RAM as their own > > dont they > You right, devices like graphic card, ethernet cards etc. are mapped > into memory, what cause some amount RAM is not available for system use. > But as i've wrote before, i'm wondering why addresses in /proc/iomem > (where the map of memory is) are not contiguous. I think, there should > be info about what region of memory is mapped where (BIOS, PCI bus, for > system use etc)*for whole 4GB *(Am I right??) address space (for 32bit > OS). Instead of that, there are small "holes" in addresses and the total > size of this holes (in my case) is about 400MB. So i wonder where that > memory is. >

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How to retrieve page pointer from vm_area_struct?
by Park Chan ho April 17, 2011

April 17, 2011

Hi all, I want to retrieve "struct page" pointer from vm_area_struct. How do I write code below example? ------------example code------------ struct task_struct *p; struct vm_area_struct *vma; struct page *page; for_each_process(p) { if (!p->mm) continue; for (vma = p->mm->mmap; vma; vma = vma->vm_next) { for (i = vma->vm_start; i < vma->vm_end; i += PAGE_SIZE) { /* How to get page pointer? */ page = ??? } } }

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Unable to remove kernel module showing permanent using lsmod
by sakthi selvam April 17, 2011

April 17, 2011

Dear All, Need your assistance: Currently I am using Wind River Linux distribution OS with kernel version 2.6.27.39 and Wind River version pne-3. After loading of my kernel module, I found it was permanent in the kernel using lsmod (for ex see below Ref 1). When I tried to remove, it was displaying as “ERROR: Removing 'hsl_module': Device or resource busy”. For your information, the same module is working fine with the Wind River pne-2 Linux Distribution OS with kernel version 2.6.21. >From the kernel source, I came to know that only possibility of showing permanent is “if there is non-availability of cleanup_module and with the availability of init_module”. But in my case, cleanup module also available in memory, after loading the module. I used to check using the file in /proc/kallsyms for the availability of cleanup module in memory. Thanks for reading. Prompt reply is expected to identify the root cause. Ref 1: Module Size Used by hsl_module 530454 0 [permanent] Thanks, Sakthi Selvam

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task snapshot mechanism
by Tharindu Rukshan Bamunuarachchi April 17, 2011

April 17, 2011

hi all, has anyone heard about or used task snapshot mechanism for Linux ? what i mean by process hibernation ... stop process , take snapshot of current state and later start/continue from the point of snapshot. (in case of failure of original process) __ Tharindu "R" Bamunuarachchi.

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Distributed Computing
by Rigved Rakshit April 17, 2011

April 17, 2011

Hi, I need help with a couple of things. I will ask them one by one. I want to "catch" a newly started process, transfer it to a remote machine, execute this process on the remote machine and then return the result to the original machine. Can anyone guide me with regard to this? Maybe if anyone could point me to the relevant documentation, then also that would be great. One possible method that I thought of is something like this: 1. Process A has just been scheduled to execute for the first time on machine A. 2. I send a suspend signal to Process A, mostly a SIGSTOP. 3. Then I copy Process A's PCB to machine B. 4. On machine B, I send the continue signal to Process A, mostly a SIGCONT. 5. Whenever Process A needs user input or needs to output something, I cause a trap, mostly with a SIGTRAP (or I could use SIGSTOP here again). I transfer this I/O request to machine A and let the user interact. I send the interaction back to Process A on machine B. I resume Process A on machine B. 6. I continue these steps till Process A has completed execution. I do not know how to do any of these (but I do know how to transfer files between two computer using rsync and how to send messages using TCP/UDP). If someone could point me in the right direction, it would be of great help to me. Thanks in advance. Regards, Rigved Rakshit

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question about alloc_bootmem
by javaweb zhang April 16, 2011

April 16, 2011

Hello, everyone. I use alloc_bootmem() in profile.c to allocate a big memory at function profile_init(), how I know whether it is success? The following is my code: // at kernel/profile.c ctxsw_A = (struct ctxsw_rec *)alloc_bootmem(sizeof(struct ctxsw_rec)*CTXSW); ctxsw_rec is a struct which declared in include/linux/profile.h, CTXSW = 4>>10

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Enabling Signals in kernel
by Vijay Ram Chitrapu April 16, 2011

April 16, 2011

Hi experts, I am using MVL6.0 in my project and have customized the kernel as per the requirement. However, i am facing a problem where the Ctrl+C signal doesn't get caught (or not sure if it is even generated) on the target platform. I have tried using the "trap" at the shell to capture the signal but the signal just doesn't get caught. Below is what i have done to try the trap way trap " " INT echo "Catching Ctrl+C signal" trap INT sleep 5 Putting this piece of code into a script doesn't catch the signal SIGINT (ctrl+c). To understand if it was a problem with the shell, i wrote a C code to register my own signal handler for SIGINT signal. To verify the correctness of the code, i executed the C code on the HOST server and it works well there (signal handler gets invoked when ctrl+c is pressed). Whereas, the same C code doesn't catch the Ctr+C signal in the target platform. Can someone tell me if there is any specific way to identify is there a way or rather is there a need to enable the signals explicitly while creating the config file for the kernel? Below is the output of "stty -a" command at the shell where i need to catch the Ctrl+C signal. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ / # stty -a speed 115200 baud; rows 24; columns 80; intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0; -parenb -parodd cs8 hupcl -cstopb cread clocal crtscts -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc -ixany -imaxbel opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Regards, Vijay

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Problem with booting using qemu
by Minwoo Lee April 16, 2011

April 16, 2011

Hi, all. I want to study kernel, so I tried booting my custom compiled kernel on qemu with '-kernel' and '-initrd' option. First, I installed ubuntu 10.10 with cdrom, no LVM. $ qemu disk.img -cdrom ubuntu-10.10-server-i386.iso -vnc :1 After installation, I tried booting my custom compiled kernel(but not modified, just compiled). $ sudo qemu -m 512 -enable-kvm disk.img -nographic -append "console=ttyS0 root=/dev/sda1 ro" -kernel bzImage -initrd initrd.img-2.6.37 And I got result like this. [ 2.687558] EXT4-fs (sda1): INFO: recovery required on readonly filesystem [ 2.688085] EXT4-fs (sda1): write access will be enabled during recovery [ 2.691679] EXT4-fs (sda1): recovery complete [ 2.944387] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null) Begin: Running /scripts/local-bottom ... done. done. Begin: Running /scripts/init-bottom ... done. [ 2.988413] e1000 0000:00:03.0: eth0: (PCI:33MHz:32-bit) 52:54:00:12:34:56 [ 2.988871] e1000 0000:00:03.0: eth0: Intel(R) PRO/1000 Network Connection After that, the machine just stopped and I don't know the cause. What is the cause, or how to find the cause? The whole log is in this url. https://gist.github.com/916961 Thank you for reading.

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Netfilter and Tcpdump
by Sowmya Sridharan April 14, 2011

April 14, 2011

Hi, I was analyzing some tcpdump data, and noticed that it also captured packets mangled by Netfilter hooks. Theoretically I know that the pcap library takes off the packets from ethernet driver level and with the help of the dynamic filters set by userspace, we are able to see those packets via tcpdump. But aren't netfilter hooks attached at a higher level, namely the network stack? If so, then how is the pcap library able to sniff those packets as well? Is it like the pcap library just holds a reference to the packets it takes from the driver, or does it maintain a separate copy for displaying? Any answers/clarifications would be much appreciated. Thanks, Sowmya =====-----=====-----===== Notice: The information contained in this e-mail message and/or attachments to it may contain confidential or privileged information. If you are not the intended recipient, any dissemination, use, review, distribution, printing or copying of the information contained in this e-mail message and/or attachments to it are strictly prohibited. If you have received this communication in error, please notify us by reply e-mail or telephone and immediately and permanently delete the message and any attachments. Thank you

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