View source for Linux memory



= Links =

*[http://www.linuxatemyram.com/ Linux ate my RAM!] 
*[https://www.thegeekdiary.com/understanding-proc-meminfo-file-analyzing-memory-utilization-in-linux/ Understanding /proc/meminfo]
*[https://www.tecmint.com/clear-ram-memory-cache-buffer-and-swap-space-on-linux/ How to Clear RAM Memory Cache, Buffer and Swap Space on Linux] 
*[http://serverfault.com/questions/377617/how-to-interpret-output-from-linux-top-command How to interpret output from Linux 'top' command?] 
*[https://linuxhint.com/understanding_vm_swappiness/ Understanding VM swappiness]
*[https://www.howtogeek.com/449691/what-is-swapiness-on-linux-and-how-to-change-it/ What is swappiness on Linux]
*https://www.kernel.org/doc/html/latest/filesystems/proc.html The /proc Filesystem]
*[https://www.fosslinux.com/47145/swappiness-linux.htm Swappiness in Linux: Everything you need to know]
*[https://serverfault.com/questions/85470/meaning-of-the-buffers-cache-line-in-the-output-of-free https://serverfault.com/questions/85470/meaning-of-the-buffers-cache-line-in-the-output-of-free] 
       
*[https://web.archive.org/web/20120520221529/http://emilics.com/blog/article/mconsumption.html Memory Consumption in Linux]
*[https://www.studytonight.com/operating-system/difference-between-paging-and-swapping Difference between Paging and Swapping]
*[https://unix.stackexchange.com/questions/2658/why-use-swap-when-there-is-more-than-enough-free-space-in-ram Why is system using swap when there is enough free space in ram?]
*[https://www.thomas-krenn.com/en/wiki/Linux_Page_Cache_Basics Linux page cache basics]

= Documentation =

 man 5 proc

see /proc/meminfo

== total ==

Is MemTotal in /proc/meminfo

Total usable ram (i.e. physical ram minus a few reserved bits and the kernel binary code)

== used ==

 total - free - buffers - cache

== unused ==

MemFree

== RSS ==

'''Resident Set Size'''

[https://stackoverflow.com/questions/7880784/what-is-rss-and-vsz-in-linux-memory-management RSS and VSZ in Linux memory management]

"memory is allocated to that process and is in RAM. It does not include memory that is swapped out. It does include memory from shared libraries as long as the pages from those libraries are actually in memory. It does include all stack and heap memory."

== VSZ / VmSize==
'''Virtual Memory Size'''
It includes all memory that the process can access, including memory that is swapped out, memory that is allocated, but not used, and memory that is from shared libraries.
*[https://www.baeldung.com/linux/resident-set-vs-virtual-memory-size RSS vs VmSize]


==ZFS and arc==
===Tools===
*arc_summary

===Links===
*[https://superuser.com/questions/1137416/how-can-i-determine-the-current-size-of-the-arc-in-zfs-and-how-does-the-arc-rel Determine arc usage]
*[https://pve.proxmox.com/wiki/ZFS_on_Linux Proxmox: ZFS on Linux]
*[https://openzfs.org/wiki/Documentation/DnodeSync arc dnode]


===Changing arc sizes in runtime===
 #in bytes
 echo 1024 > /sys/module/zfs/parameters/zfs_arc_min
 echo 2048 > /sys/module/zfs/parameters/zfs_arc_max
===Changing arc settings===
In /etc/modprobe.d/zfs.conf: 
 options zfs zfs_arc_max=4294967296
 options zfs zfs_arc_min=1073741824


'''If root on ZFS''' (really?)
 update-initramfs -u -k all

= FAQ =

== What is using all my memory? ==

 smem -r -s swap| head -n3


==What is using all my swap? ==
https://www.cyberciti.biz/faq/linux-which-process-is-using-swap/

 for file in /proc/*/status ; do awk '/VmSwap|Name/{printf $2 " " $3}END{ print ""}' $file; done | sort -k 2 -n -r | less
or to just list top 3
 for file in /proc/*/status ; do awk '/VmSwap|Name/{printf $2 " " $3}END{ print ""}' $file; done | sort -k 2 -n -r | head -n 3


==Watch buffer/cache activity==
https://www.heroix.com/blog/linux-memory-use/
 sar -B


==What is in buffer/cache?==
===Tools===
*[https://github.com/brendangregg/perf-tools perf-tools]
*https://www.brendangregg.com/blog/2014-12-31/linux-page-cache-hit-ratio.html

== Clear buffer/cache ==

 sync; echo 3 > /proc/sys/vm/drop_caches