What does all the RAM information in overview page mean?

Dear all,

I am completely confused by to displayed information in the overview page.

There are total available, used, buffered, cached. What does these all mean?

Thank you!

https://man7.org/linux/man-pages/man1/free.1.html

Thanks.

In the page you linked, it says
used Used memory (calculated as total - free - buffers - cache)

But I got 97% used, 11% buffered, 76% cached.

If "total - free - buffer - cache = used" , it just does not add up

Please compare the figures with calling free via ssh, I think "Used" might aggregate the actually used RAM with buffers and cache.

OK will do later today.

I just feel the current luci overview of RAM is completely a mess.

2 Likes
  • total available - Available RAM (MemAvailable) as reported by /proc/meminfo - this is the kernel's estimate of RAM actually available to applications. This figure also includes some buffer and cache memory because such memory would be given to applications under memory pressure (see also longer explanation at https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773)
  • used - This is MemTotal - MemFree basically the total addressable system RAM minus the amount of ram the kernel considers to be untouched
  • buffers - Memory used for disk buffering (might be absent on some devices)
  • cached - Memory used for filesystem caching

These values are not supposed to add up, they rather provide different indications about memory utilization:

  • available - this is usually what you need to look at to see if your applications and services have memory to work with, it includes free and untouched ram as well as ram that would be reclaimed by the kernel and made available to applications even if it is in use right now for disk buffering, inode caching etc.
  • used - gives an indication about how much ram is "touched" right now by the system, regardless of whether it is reclaimable or permanently in use (MemTotal - MemFree)
  • buffers - Outlines the amount of ram used for block device caching, if this number is high you do have a lot of IO activity on slow disks
  • cached - Outlines the amount of ram used for filesystem caching. If this number is high you do have a lot of random access IO activity and high application memory usage might steal away this cache memory, impacting average filesystem access performance
8 Likes

Thank you so much for this write-up!

Your elaborated explanation benefits a lot of people like me, who is having trouble figuring out the exact meaning of it.

In my case, I have transmission running in the background uploading torrents, which explains the high "cached" count. I guess if any other application claims those RAM, it will impact the filesystem performance like you mentioned.

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