An active RHEL system should be using almost all of the free physical memory for cache and buffers. Once you start doing application I/O, you'll see the memory get "used" by the OS quickly. Remember, the memory "used" for cache/buffers is actually free and the kernel can reclaim it very quickly if memory demand for processes increases. The "free" command shows you the difference between "used" memory with and without including the cache/buffers.
Older versions of Linux did have a penalty for very large memory because the algorithms used to manage memory pages were primitive. Many of those problems were addressed in later RHEL 4 releases and by the time we got to RHEL 5 and 6, those issues have been completely resolved. Many of our servers run 256 or 512GB of RAM. For a BL460c with maybe 8 cores, 32GB seems to me to be about right. If it's a BL460cG6 with 16 cores, 32GB seems small. It all depends on what applications or databases you're running on it.
Here's an example from a mid range system with 48 cores:
At first glance it looks like this system has no free memory. But the actual memory used by processes is actually only 24GB - the other 226GB is cache/buffers.
With very large amounts of RAM on certain hardware you can encounter NUMA issues, but as a general rule, you can never have too much memory. RHEL will find a way to use it.
Hello,
I need explanations about physical disks and physical volumes. What is the difference between these 2 things?
In fact, i am trying to understand what the AIX lspv2command does.
Thank you in advance. (2 Replies)
I was in smit, checking on disc space, etc. and it appears that one of our physical volumes that is part of a large volume group, has no free physical partitions. The server is running AIX 5.1. What would be the advisable step to take in this instance? (9 Replies)
Hi All,
I am trying to find the physical memory usage by each process/users.
Can you please let me know how to get the memory usage?.
Thanks,
bsraj. (12 Replies)
Hello All,
Can anybody please tell me what is the maximum limit of Physical IBM Power Machine which can be handled by single HMC at a single point of time?
Thanks,
Jenish (1 Reply)
I have a Sun T5120, and I want to programmatically determine how much RAM it has.
# uname -a
SunOS myhost 5.10 Generic_141444-09 sun4v sparc SUNW,SPARC-Enterprise-T5120
The box has 64Gb; I tried prtdiag and prtconf, but they give me bogus info
prtconf gives me:
# prtconf |grep -i... (12 Replies)
After a memory upgrade all network interfaces are misconfigued. How do i resolve this issue. Below are some out puts.thanks.
ifconfig: plumb: SIOCLIFADDIF: eg000g0:2: no such interface
# ifconfig eg1000g0:2 plumb
ifconfig: plumb: SIOCLIFADDIF: eg1000g0:2: no such interface
# ifconfig... (2 Replies)
Hi,
I am new to unix. I am working on Red Hat Linux and side by side on AIX also. After reading the concepts of Storage, I am now really confused regarding the terminologies
1)Physical Volume
2)Volume Group
3)Logical Volume
4)Physical Partition
Please help me to understand these concepts. (6 Replies)
Hi,
kstat -p -m zfs -n arcstats -s size returns
zfs:0:arcstats:size 8177310584
this values is approx (7.61 GB)
but my Physical Memory size is only 6144 Megabytes.
Can this happen ?
if yes, then how can I find free memory on the system.
BTW, I ran the kstat commands from a Non... (2 Replies)
Discussion started by: sapre_amit
2 Replies
LEARN ABOUT OPENSOLARIS
bcopy
bcopy(9F) Kernel Functions for Drivers bcopy(9F)NAME
bcopy - copy data between address locations in the kernel
SYNOPSIS
#include <sys/types.h>
#include <sys/sunddi.h>
void bcopy(const void *from, void *to, size_t bcount);
INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI).
PARAMETERS
from Source address from which the copy is made.
to Destination address to which copy is made.
bcount The number of bytes moved.
DESCRIPTION
The bcopy() function copies bcount bytes from one kernel address to another. If the input and output addresses overlap, the command exe-
cutes, but the results may not be as expected.
Note that bcopy() should never be used to move data in or out of a user buffer, because it has no provision for handling page faults. The
user address space can be swapped out at any time, and bcopy() always assumes that there will be no paging faults. If bcopy() attempts to
access the user buffer when it is swapped out, the system will panic. It is safe to use bcopy() to move data within kernel space, since
kernel space is never swapped out.
CONTEXT
The bcopy() function can be called from user, interrupt, or kernel context.
EXAMPLES
Example 1 Copying data between address locations in the kernel:
An I/O request is made for data stored in a RAM disk. If the I/O operation is a read request, the data is copied from the RAM disk to a
buffer (line 8). If it is a write request, the data is copied from a buffer to the RAM disk (line 15). bcopy() is used since both the RAM
disk and the buffer are part of the kernel address space.
1 #define RAMDNBLK 1000 /* blocks in the RAM disk */
2 #define RAMDBSIZ 512 /* bytes per block */
3 char ramdblks[RAMDNBLK][RAMDBSIZ]; /* blocks forming RAM
/* disk
...
4
5 if (bp->b_flags & B_READ) /* if read request, copy data */
6 /* from RAM disk data block */
7 /* to system buffer */
8 bcopy(&ramdblks[bp->b_blkno][0], bp->b_un.b_addr,
9 bp->b_bcount);
10
11 else /* else write request, */
12 /* copy data from a */
13 /* system buffer to RAM disk */
14 /* data block */
15 bcopy(bp->b_un.b_addr, &ramdblks[bp->b_blkno][0],
16 bp->b_bcount);
SEE ALSO copyin(9F), copyout(9F)
Writing Device Drivers
WARNINGS
The from and to addresses must be within the kernel space. No range checking is done. If an address outside of the kernel space is
selected, the driver may corrupt the system in an unpredictable way.
SunOS 5.11 16 Jan 2006 bcopy(9F)