Cache memory is free memory with benefits. Having nearly 100% memory as cache means you have nearly 100% memory free.
If you're dropping caches all the time in linux you're throwing away your disk cache all the time, forcing your disk to be read again to get them back into memory when needed.
Last edited by Corona688; 02-05-2013 at 01:46 PM..
@Corona688:
... provided the Linux VM would be perfect.
Do continues I/O until the buffer cache is near 100%, and while doing further I/O start a big Java application. It will take AGES, even an OOM can occur. At least on some Linux kernels.
Do the drop_caches trick, and the Java application will start FAST.
I'm a little late to this thread, but what kind of file system(s) are being used on the servers?
Oracle DB processes tend to request large memory pages, while the ZFS ARC uses small memory pages.
When memory gets tight - such as the servers in question - the kernel spends an inordinate amount of time coalescing large pages for Oracle then breaking them apart for ZFS.
Over and over and over.
Try running this dtrace script when things are slow:
That will tell you where your kernel is spending it's time. If you see lots of "coalesce" in the output after you break a running copy of that script, that's your problem.
Free up some memory - lower your Oracle SGA, severely limit your ZFS ARC size, etc.
Do continues I/O until the buffer cache is near 100%, and while doing further I/O start a big Java application. It will take AGES, even an OOM can occur. At least on some Linux kernels.
Sounds like it's time to upgrade your kernel, then.
And this has nothing to do with it refusing to drop cache. It's because java is not in cache; other activity has gradually cleaned it out, and everything must be reloaded from disk, while the disk is already busy.
Quote:
Do the drop_caches trick, and the Java application will start FAST.
Relying on these tricks is a bad idea. Something more fundamental is out of whack.
Last edited by Corona688; 02-12-2013 at 05:10 PM..
If I understand your question correctly, you are asking for an explanation of Solaris memory manager. You'd better ask Oracle that question because you are talking about Solaris kernel internals.
The operating system kernel has no reason to kick a process's memory set out of real memory until... (4 Replies)
Hi guys.
I've a question, if we are using a syscall that receives a string allocated dynamicaly to a determined size, or NUL and it will allocate the apropriate size. We should free the memory or the OS will do it for us?
If a function returns a pointer we should free that poiter when we are done... (7 Replies)
I was running a program and it stopped and showed "Out of Memory!". at that time, the RAM used by this process is around 4G and the free memory size of the machine is around 30G. Does anybody know what maybe the reason? this program is written with Perl. the OS of the machine is Solaris U8. And I... (1 Reply)
hi, I have done the below, but am confused as to how much memory is "free"
please help
thanks
$ free
total used free shared buffers cached
Mem: 132033488 48827536 83205952 0 1007696 45404632
-/+ buffers/cache: 2415208 ... (7 Replies)
Hi all,
Could please let me know how to get the more memory free space (not added the RAM) in local zone.
-bash-3.00# vmstat 2 5
kthr memory page disk faults cpu
r b w swap free re mf pi po fr de sr s0 s1 s1 s1 in sy cs us sy... (3 Replies)
Hi,
Im working on Solaris 9 on SPARC-32 bit running on an Ultra-80, and I have to find out the following:-
1. Total Physical Memory in the system(total RAM).
2. Available Physical Memory(i.e. RAM Usage)
3. Total (Logical) Memory in the system
4. Available (Logical) Memory.
I know... (4 Replies)
HI
I'm a rookie in C programming and I'm working in Monta Vista Linux. I have to write a program that displays free memory. I have memtester(allready written by someone else) and now I have to type how much amount of memory tester will test and I want that memtester finds out himself how much of... (11 Replies)
For example if i have the piece of code as follows:
CountryName = (char *)malloc((strlen(CountryName)+1)*sizeof(char));
memset(CountryName, 0, strlen(CountryName)+1);
CountryName = SOME VALUE
Now how do i free the memory after use of this code???? :confused: (3 Replies)