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1
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0answers
426 views

Where does the Linux kernel reside in memory ?

From some book I have, I have in my notes that the Linux kernel resides at 0xc00000000 on 32-bit systems, and is mapped into user space for performance reasons. Is this accurate ? How can I verify ...
3
votes
2answers
288 views

Misleading explanation of Virtual Memory in TLDP

I'm completely confused about explanation of virtual memory in TLDP: http://www.tldp.org/LDP/tlk/kernel/processes.html#tthFtNtAAB They say: Each individual process runs in its own virtual ...
0
votes
1answer
835 views

What does m represents in VIRT column using TOP command

When we run top command it shows all the processes information. But under VIRT column there is m written against some values what does that m represents, is it MB . If yes then why it is only showing ...
4
votes
3answers
124 views

What is contained in these addresses?

I am working on MUlti-processor record-replay feature of a virtual machine. I have a log of non-deterministic memory access done in the virtual machine by virtual CPUs. A very high proportion of these ...
1
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1answer
1k views

Drop_caches doesn't drop caches?

Sometimes I see my swap file is a bit bigger then usual. I tried sync && echo 3 > /proc/sys/vm/drop_caches to no avail. But when I tried swapoff -a it takes a bit longer but the swap file ...
-1
votes
2answers
540 views

What would be a light weight, memory non-intensive distro for virtual server use?

I have come across several posts talking about light weight distros from a general context, but none of them are really hitting the nail on the head for me. Specifically, I have PHP script that I run ...
2
votes
1answer
1k views

How to debug Linux kernel panic?

I am trying to debug a kernel panic. Panic message says unable to handle kernel paging request for address 40025694. At the time of panic it was executing ldreq r10, [lr, #-4] @ get SWI instruction. ...
7
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2answers
1k views

An oom killer thats baffling me

I am not able to understand why would kernel issue this oom killer when I see enough memory is available: Also why are there so many kernel cache pages allocated? I say enough memory is available ...
3
votes
1answer
489 views

Rationale for making user space text segment start at 0x8048000

I read somewhere that (at least since Linux v. 2.6) all user-space code is placed at load address 0x8048000 in the virtual memory address space. My own observations confirm this. I have done a cat ...
1
vote
2answers
261 views

Sudden burst in free memory

I'm experiencing some strange memory management behaviour on Squeeze with Kernel 2.6. I'm trying to get to the bottom of this with nmon. Sometimes this will freeze up the system for 30 seconds to 5 ...
3
votes
0answers
593 views

How extended (4MB) and regular (4KB) paging coexist?

On x86 architecture, "Extended paging" allows page frames (physical memory) to be 4 MB instead of 4 KB. The book "Understanding the Linux Kernel, 3rd" at chapter 2 "Memory Addressing", sub-chapter ...
2
votes
1answer
151 views

Memory Management: Faulting virtual addresses

I came across the following on http://tldp.org/LDP/tlk/mm/memory.html If the faulting virtual address is invalid this means that the process has attempted to access a virtual address that it ...
1
vote
2answers
489 views

NAND flash memory wear & virtual memory page swap

For a linux kernel with virtual memory and disk storage, pages are swapped back and forth into swap area. But embedded systems generally use NAND flash instead of disk. A NAND flash has a limited ...
3
votes
2answers
911 views

How much RAM can an application allocate on 64-bit x86 Linux systems?

Is it true that a single application can not allocate more than 2 GiBs even if the system has GiBs more free memory when using a 32-bit x86 PAE Linux kernel? Is this limit loosened by 64-bit x86 Linux ...
2
votes
1answer
938 views

How often is PSS value updated for a given process in /proc/pid/smaps

So if n processes are sharing a library L with size M then the contribution to their PSS is M/n. Now imagine one of the process terminates. So the contribution would be M/(n-1). Q1: My question is ...
18
votes
1answer
13k views

Getting information about a process' memory usage from /proc/pid/smaps

For a given process in /proc/<pid>/smaps, for a given mapping entry what are: Shared_Clean Shared_Dirty Private_Clean Private_Dirty Is Shared_Clean + Shared_Dirty the amount of memory that ...
0
votes
1answer
282 views

Reading virtual memory

Is it possible to read virtual memory even if /dev/kmem is not available? I know that I can recompile kernel to allow this file, but that's not the solution I'm looking for. Is there some tricky way I ...
3
votes
1answer
631 views

tmpfs and vm.swappiness

I have started tuning a bit Linux VM performance on my system (yes. I know that vm.swappiness=0 will kill kittens but I found 30-40 as much better for me as it improved my latency - probably at cost ...
6
votes
1answer
867 views

User Kernel split in 64bit Linux

What is the default user/kernel split in the 64bit linux ? I read Documentation/x86_64/mm.txt (which someone pointed out), but I could not make out. Can somebody provide a direct answer (something ...
3
votes
1answer
1k views

Solaris swap allocation with mlocked shared memory

I'm having a hard time understanding how Solaris 10 x86 swap allocations work in the presence of mlocked share memory. I wrote a small program that: Gets a 1G SHM segment (shmget) Attaches it to ...
10
votes
1answer
10k views

Setting /proc/sys/vm/drop_caches to clear cache

As part of doing some cold cache timings, I'm trying to free the OS cache. The kernel documentation says: drop_caches Writing to this will cause the kernel to drop clean caches, dentries and inodes ...
6
votes
3answers
2k views

How to set up properly zram and swap

I'm configuring & compiling new 3.0 kernel. One of the goodies I planned to use for some time (by patching) that was merged into 3.0 is zram. Is it possible to set both hdd swap and zram swap so ...
9
votes
1answer
4k views

Unable to handle kernel paging request?

[Disclaimer: I was initially a little nervous about posting this here, so I asked on Meta if discussing homebrew / modding was acceptable. Based on the response I've gotten from several veteran ...
2
votes
3answers
2k views

How is paging managed in the absence of swapping?

How is paging managed in the absence of swapping. If that is the case, how will a page fault be managed? What I meant is, if there is no availability for swapping, then how is Paging managed. I ...