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?
View 4 RepliesWhy linux uses swap space, even if there are free physical memory available.
View 4 Replies View RelatedAs 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?
I have a system with 2G of memory and swap memory of 4G.
This is the output from :
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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.
clarify me with ulimit output and memory limit?
ulimit -a output:
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) 1572864
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Logical Memory Space of 4GB is divided in to 3GB User Space and 1GB Kernel Space. Always. Correct?
1. How can we change it? (just changing value of PAGE_OFFSET is okay?)
2. If system have only 256MB of memory (embedded system) and suppose Kernel Modules eat away all the memory during boot. User space will be left will no memory. Is this case possible?
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.
View 3 Replies View Relatedlet me know how to clear cache memory ( RHEL 5.1 ) as it consumes almost 100% physical memory.
View 3 Replies View RelatedI 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?)
View 4 Replies View RelatedI 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?
View 1 Replies View RelatedI 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?
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.
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 ?
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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.
RAM for older machines like I use is fairly cheap these days. But flash memory is just as cheap or cheaper. So I'd like to ask about the feasibility of expanding my system's memory using flash memory. And about whether creating a partition for swap on the flash memory, or whether a swap file on the flash device, is the better way to go.
By flash memory I have in mind mainly USB sticks or what are sometimes called "pen drives." But I do also have CF and SD cards that, with the proper cheap adapter (one of which I already own for adapting CF) could be used to create extra swap space. So, what is the current consensus on the feasibility/advisability of using flash memory for swap? I've read about the limited write cycles of flash being an argument against using it for swap. But recent reading indicates to me that the limited write cycles problem applies mostly to older, smaller-capacity flash memory. Some will come out and say that, for larger-capacity flash memory, the life of the device is likely to exceed the amount of time your current computer will be useful (I think I've seen estimates in the range of 3-4 years life--minimum--for newer, higher-capacity flash memory).
A more persuasive argument I've heard against using flash memory for swap is that access times for these devices can be much slower than SATA, and maybe even IDE, hard drives. That would certainly dictate against using flash memory for swap.
So, how about some input on this issue? Anyone using flash memory for swap? If so, what kind (e.g., usb stick or SD/CF)? Are you using a swap file or a swap partition? How's system performance? Likewise, has anyone had flash-memory-used-as-swap die on them? The consequences would undoubtedly be dire. Also, has anyone measured flash memory access times to confirm or refute claims about slow access times? Are some types of flash memory better/worse than others in terms of access times?
Lucid on an Acer Travelmate800.Can anyone tell me why I have 0k for swap space? I allocated swap which I can see in my Disk Utility's 'volumes' display.
View 5 Replies View RelatedThere are plenty of tools for umounting/mounting/automounting usb flash/pen drives/dongles/hard drives. There's the Device Notifier on kde 4, for example.
But what about other devices like headphones, mice, keyboards, modems, etc? A tool for doing this would be very handy.
I came across this article, which I found to be very interesting and thought share it with you all.
Graphics CardMemory as swap space or RAM disk.
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a friend of mine recently installed Ubuntu in his Laptop however is running really slow. It's Dell 1520 so I don't think the computer is that slow. I think what the problem is that he doesn't have a swap space. ok, I could use GPARTED to resize the HD and create SWAP space but how can I tell the system to permanently use that space?
View 14 Replies View RelatedI have a rel 5.6 system that we just added more memory to.
1. What is the correct or best way to increase swap?
2. Can I remove the swap space later on?
3. How do you remove it when done?
Our rootvg only has 8G available to it and I want to be sure if i allocate anything out to it I can reclaim when done without having to rebuild the system.
We have to do a lot of data moves so we allocated extra memory to this VM system and now we need to increase swap. I did see several articles in google but they describe using a new swap partition, a swap file and increasing an existing swap space. I am still not sure what is the best way to go knowing this is a temp situation.
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How can I figure out which programs are using up swap space? My current memory usage is 2.9GiB out of 3.0GiB used(and I though I had 4GB, I need to check into that) and 1.3Gib of swap used.
View 1 Replies View RelatedI have a linux server top reports about 9GB of swap used:But I cannot figure where's it use swap, some google results said that top - O commad follow by p will show swap usage by process. But as shown in the above image, taking a brief sum of the SWAP column shows that > 10GB of swap is used, so where does the 9GB figure for swap usage come from? Top reports that about 96492kb of ram is used by buffers. Is there anything I can do to utilize this, instead of using swap?
View 1 Replies View RelatedI run a memory-hungry process (mkcromfs) which consumes more memory than I have physical memory on my latop, so it is paging and swappin and thrashing all the time and loadavg is about 2 (compcache is already in use with usual swap partition as well), but slowly moving forward (Although I afraid it will finally try to allocate >2GB and crash draining 2 days of thrashing).
When I want to use the laptop for something else, I stop the process, start X server, firefox and other programs. The problem is that when I start Firefox the loadavg jumps to 10 and the system becomes almost unresponsive at all (long time to turn on/off caps lock, slow mouse cursor position updates, slow switching from X server to Linux console, slow login).
The stopped mkcromfs still holds a lot of memory (464.8 MiB and slowly falling) and moves it to swap only when more memory is needed for some other program, which results in a great slowdown.
How to tell the Linux to swap out this process entirely (e.g. I'm not intending to resume it in short term), possibly waking from swap other data? Also it will be useful to be able to specify the exact swap device to swap the given process out (for example, mkcromfs's memory is useless in ramzswap).
Update: Now I just write a 400-600M of data from /dev/erandom to tmpfs and it makes mkcromfs to shrink. Is there more proper way?
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but 'top' shows 2GB of swap...
top - 18:38:42 up 4:22, 5 users, load average: 0.54, 0.61, 0.64
Tasks: 369 total, 1 running, 368 sleeping, 0 stopped, 0 zombie
Cpu(s): 7.4%us, 1.4%sy, 0.0%ni, 86.9%id, 3.4%wa, 0.0%hi, 0.9%si, 0.0%st
Mem: 33265832k total, 24859468k used, 8406364k free, 379892k buffers
Swap: 2031608k total, 0k used, 2031608k free, 2030328k cached
Why is that?
We're load testing some of our larger servers (16GB+ RAM), and when memory starts to run low they are kicking off the oomkiller instead of swapping. I've checked swapon -s (which says we're using 0 bytes out of 16GB of swap), I've checked swappiness (60), I've tried upping the swap to 32GB, all to no avail. If we pull some RAM, and configure the box with 8GB of physical ram and 16 (or more) GB of swap, sure enough it dips into it and is more stable than a 16GB box with 16 or 32GB of swap.
View 6 Replies View RelatedClosest analogy I can compare what I want to, is like the `sync` command, which writes out all stuff in the disk buffers, freeing the buffers.Instead of disk buffers, I want to 'clean out' my RAM and SWAP of any/all junk that's accumulated in there over the time my PC has been up. I've long wondered about this, but never asked, though I recall searching around several times..When I first boot it cold and log in, the memory usage bar on my desktop is near zero, and the swap is empty. But after a week or 2 or 3 or more of uptime, and with Firefox always running with a dozen tabs or so at any given time, I end up with all the memory full or 'filled with cached stuff', and the swap space is filled to capacity.Curiousity: I blame Firefox for leaking memory, but even if that's still the case today (historically it was) can this all be blamed on Firefox? Or what-all causes this, besides Firefox- just..Everything?
Here's current stats:
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sasha@reactor: uptime
21:21:42 up 30 days, 10:07, 3 users, load average: 0.02, 0.05, 0.01
sasha@reactor: free
total used free shared buffers cached
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So, 3.8 of 4 Gib of RAM is occupied, and the 1 Gib swap space is jammed full 100%. This must slow things down to some degree, yes? I mean, the kernel does have to keep track of this, right?Of course closing all the applications doesn't make a difference (not an appreciable one anyhow) and the only way I have found to start fresh is to reboot.
Wish a script which would delete cache content and remove additional files which have been downloaded via the internet and saved voluntarily by the user and files any thing other than those used by the OS in linux.Need a command which could make the execution of the above script possible before the shut down command is passed.
View 1 Replies View RelatedWhile booting Linux it takes ages for 'enabling swap space'
I have allocated swap space twice that of the RAM.
Is there a way to fix it? What should I do to avoid this in the future installs?
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 .
How can I get the physical address corresponding to a virtual address in linux by using /proc file system
View 1 Replies View RelatedI got the VMrss used by a process as about 2GB, but the physical memory of my computer is only 1G.
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