12-15-2018
Quote:
Originally Posted by
javanoob
Back to the reason on the post
- I have 3GB of swap disk used (in swap -l)
- I have 10GB+ of free physical RAM
- I have 0 scanrate and vmstat available swap = 37GB
Since i am 10G of physical ram and 0 SR - i am not short on ram
Since i have 37GB of virtual swap available - i am not short on virtual swap
What could have contributed to the 3GB swap disk ?
Three gigabytes of memory were used (i.e. read/written) sometime in the past by some process(es). They have not been accessed for a while so the kernel decided to put the data on disk, to keep the free RAM high.
Quote:
Could it be at some point of time, i am running low on physical ram and swap/paging need to be done ?
You need not to starve on RAM for paging to occur.
Quote:
When does physical space used in swapdisk be release ?
When the processes owning it will die.
Quote:
It is gradually increasing (slow.. but like 5-10MB more of swapdisk used per week) - that is the worrying part.
That might be just some optimization done by the kernel.
There might be a memory leak in a process, 10 MB per week is not among the fiercest ones.
There might be a growing file in /tmp or any tmpfs based file system. The storage area of tmpfs is virtual memory (not any process virtual memory but the OS virtual memory, i.e. RAM + SWAP as Bakunin wrote).
Note also the free memory might be actually used by the kernel, which isn't constrained by process virtual memory rules.
Solaris uses free memory as UFS and NFS cache, so this free memory contains actual data, but it is nevertheless reported as free by vmstat and similar commands, because it is immediately available for processes allocations.
Last edited by jlliagre; 12-15-2018 at 06:36 PM..
This User Gave Thanks to jlliagre For This Post:
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MD(4) BSD Kernel Interfaces Manual MD(4)
NAME
md -- memory disk
SYNOPSIS
device md
DESCRIPTION
The md driver provides support for four kinds of memory backed virtual disks:
malloc Backing store is allocated using malloc(9). Only one malloc-bucket is used, which means that all md devices with malloc backing
must share the malloc-per-bucket-quota. The exact size of this quota varies, in particular with the amount of RAM in the system.
The exact value can be determined with vmstat(8).
preload A file loaded by loader(8) with type 'md_image' is used for backing store. For backwards compatibility the type 'mfs_root' is also
recognized. If the kernel is created with option MD_ROOT the first preloaded image found will become the root file system.
vnode A regular file is used as backing store. This allows for mounting ISO images without the tedious detour over actual physical media.
swap Backing store is allocated from buffer memory. Pages get pushed out to the swap when the system is under memory pressure, otherwise
they stay in the operating memory. Using swap backing is generally preferable over malloc backing.
For more information, please see mdconfig(8).
EXAMPLES
To create a kernel with a ramdisk or MD file system, your kernel config needs the following options:
options MD_ROOT # MD is a potential root device
options MD_ROOT_SIZE=8192 # 8MB ram disk
makeoptions MFS_IMAGE=/h/foo/ARM-MD
options ROOTDEVNAME="ufs:md0"
The image in /h/foo/ARM-MD will be loaded as the initial image each boot. To create the image to use, please follow the steps to create a
file-backed disk found in the mdconfig(8) man page. Other tools will also create these images, such as NanoBSD.
SEE ALSO
disklabel(8), fdisk(8), loader(8), mdconfig(8), mdmfs(8), newfs(8), vmstat(8)
HISTORY
The md driver first appeared in FreeBSD 4.0 as a cleaner replacement for the MFS functionality previously used in PicoBSD and in the FreeBSD
installation process.
The md driver did a hostile takeover of the vn(4) driver in FreeBSD 5.0.
AUTHORS
The md driver was written by Poul-Henning Kamp <phk@FreeBSD.org>.
BSD
October 30, 2007 BSD