Re: [OT]What is "buffers" and "cached" memory in Linux system box?

in reply to [OT]What is "buffers" and "cached" memory in Linux system box?

What should I think of the "buffers" and "cached" memory? should I think they are part of free memory?

This is a verbatim copy of what I wrote down when I had this same question:

             total       used       free     shared    buffers     cac
+hed
Mem:       1034332     983572      50760          0     149028     530
+132
-/+ buffers/cache:     304412     729920
Swap:       131064       9856     121208

Mem:             A          B          C          D          E        
+  F
-/+ buffers/cache:          G          H

G+H = A
E+F+G = B   ## probably D+E+F+G
C+E+F = H   ## probably C+D+E+F
[download]

--
David Serrano

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Re^2: [OT]What is "buffers" and "cached" memory in Linux system box? by sunshine_august (Scribe) on Sep 20, 2008 at 03:33 UTC
I try to rearrange the expression to make it more clear: `A = B + C = G + H G = B - E - F H = C + E + F` [download] It seems that: Mem: 1034332 983572 50760 0 149028 530132 shows "buffers" and "cached" as part of "used" memory. But -/+ buffers/cache: 304412 729920 shows "buffers" and "cached" as part of "free" memory The -/+ buffers/cache line shows how much memory is used and free from the perspective of the applications. --- from http://gentoo-wiki.com/FAQ_Linux_Memory_Management#The_difference_between_buffers_and_cache And I do a test on my box, it shows that when the "free" memory is going to be exhausted, the kernel will take back all the "buffers" memory, but still left some "cached"memory. Following is the output by "free -m -s 1" when I increasingly created threads to consume the memory: `total used free shared buffers cac +hed Mem: 7973 68 7904 0 8 + 27 -/+ buffers/cache: 33 7939 Swap: 2047 0 2047 total used free shared buffers cac +hed Mem: 7973 106 7866 0 8 + 27 -/+ buffers/cache: 71 7902 Swap: 2047 0 2047` [download] Read more... (4 kB)	[reply] [d/l] [select]

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Re^2: [OT]What is "buffers" and "cached" memory in Linux system box?
by sunshine_august (Scribe) on Sep 20, 2008 at 03:33 UTC

A = B + C = G + H
G = B - E - F
H = C + E + F
[download]

Mem: 1034332 983572 50760 0 149028 530132
shows "buffers" and "cached" as part of "used" memory.

But -/+ buffers/cache: 304412 729920
shows "buffers" and "cached" as part of "free" memory

The -/+ buffers/cache line shows how much memory is used and free from the perspective of the applications.
--- from http://gentoo-wiki.com/FAQ_Linux_Memory_Management#The_difference_between_buffers_and_cache

And I do a test on my box, it shows that when the "free" memory is going to be exhausted, the kernel will take back all the "buffers" memory, but still left some "cached"memory. Following is the output by "free -m -s 1" when I increasingly created threads to consume the memory:

             total       used       free     shared    buffers     cac
+hed
Mem:          7973         68       7904          0          8        
+ 27
-/+ buffers/cache:         33       7939
Swap:         2047          0       2047

             total       used       free     shared    buffers     cac
+hed
Mem:          7973        106       7866          0          8        
+ 27
-/+ buffers/cache:         71       7902
Swap:         2047          0       2047
[download]