New on LowEndTalk? Please Register and read our Community Rules.
All new Registrations are manually reviewed and approved, so a short delay after registration may occur before your account becomes active.
All new Registrations are manually reviewed and approved, so a short delay after registration may occur before your account becomes active.
Xen PV wrong memory amount
Hello all,
I've bought a Xen PV VPS with 512 MB of RAM and 512 MB of Swap, but when I execute free -m I see:
total used free shared buffers cached
Mem: 497 46 451 0 1 22
-/+ buffers/cache: 21 475
Swap: 511 0 511
Is reserved by the kernel or what?
I haven't had this problem with others Xen VPS.
But if I reload the VPS using the CentOS 5 i386 template I get 512 MB of RAM...
The CentOS 5 template is the only that "works".
Is something that I can fix?
Comments
What is the problem?
Where are the remaining 15 MB of memory?
Im guessing its because the VPS shows 497MB of RAM, when he should have 512MB.
I believe that is caused by PyGrub, if you use a 64bit OS you should have more available RAM than a 32bit OS. I didn't test this extensively but I think that's the reason.
You can also use PAE to address the full memory amount.
I get even less memory with CentOS 6 x86_64
total used free shared buffers cachedMem: 489 67 422 0 1 22
-/+ buffers/cache: 43 446
Swap: 511 0 511
Can I ask why are you using 64 bits on a 512MB VPS ?
No PyGrub should result in more available memory. Guess I was wrong.
The kernel uses some of your RAM.
I have an 80MB xen box and when I switch from Debian 5 to Debian 6 with pygrub (both 32 bit) the RAM dropped to 73MB. pygrub uses more memory.
Sometimes the RAM is reserved by certain things.
Give the output of cat /proc/iomem
That will tell us what's exactly using your memory.
total used free shared buffers cached
Mem: 489 67 422 0 1 22
512MB = 488MiB :-)
Wouldn't 512 Megabytes be 4096 Megabits?
MB = Megabyte
MiB = Mebibyte
Mb = Megabit
Why binary?
Sometimes the RAM is reserved by certain things.
Give the output of cat /proc/iomem
That will tell us what's exactly using your memory.
This is from the 80MB box that shows 73MB total with pygrub. It doesn't mean anything to me.
it's likely the 'video card' eating some of it.
Francisco
@efball it simply shows what memory address's are being used for.
Here's some more data. All are using Debian 6:
So the pygrub xen boxes aren't any worse than KVM.
My Xen PV VPS have 2GB RAM but showing only 1.83GB RAM. What seems to be the problem?
Xen does not always report memory correctly through free -m
Run: cat /proc/meminfo
Near the bottom you should see: driectmap 4k, that is how much ram your VPS can actually use, if you see the wrong number in there then you have a problem but I suspect everything will be in order
Thanks.
On a KVM with 128mb memory:
I added the 2 numbers up and got 127.99mb.
@dmmcintyre3 not sure what that means in KVM as you dont get a dedicated memory allocation, you dont need to do anything special in KVM to vastly oversell ram so I guess what I said is only applicable on XenPV.
At a guess I would say that the total you see is what you have in use as that is all the host node needs to allocate to you at the time?
Just wondering, it actually reserved for what?