What is the difference between buffer and cache memory in Linux?

To me it's not clear what's the difference between the two Linux memory concepts : buffer and cache. I've read through this post and it seems to me that the difference between them is the expiration policy:

1. buffer's policy is first-in, first-out
2. cache's policy is Least Recently Used.

Am I right?

In particular, I'm looking at the two commands: free and vmstat

james@utopia:~$ vmstat -S M
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
5  0      0    173     67    912    0    0    19    59   75 1087 24  4 71  1
james@utopia:~$ free -m
             total       used       free     shared    buffers     cached
Mem:          2007       1834        172          0         67        914
-/+ buffers/cache:        853       1153
Swap:         2859          0       2859

Solution 1:

Buffers are associated with a specific block device, and cover caching of filesystem metadata as well as tracking in-flight pages. The cache only contains parked file data. That is, the buffers remember what's in directories, what file permissions are, and keep track of what memory is being written from or read to for a particular block device. The cache only contains the contents of the files themselves.

quote link

Solution 2:

Cited answer (for reference):

Short answer: Cached is the size of the page cache. Buffers is the size of in-memory block I/O buffers. Cached matters; Buffers is largely irrelevant.

Long answer: Cached is the size of the Linux page cache, minus the memory in the swap cache, which is represented by SwapCached (thus the total page cache size is Cached + SwapCached). Linux performs all file I/O through the page cache. Writes are implemented as simply marking as dirty the corresponding pages in the page cache; the flusher threads then periodically write back to disk any dirty pages. Reads are implemented by returning the data from the page cache; if the data is not yet in the cache, it is first populated. On a modern Linux system, Cached can easily be several gigabytes. It will shrink only in response to memory pressure. The system will purge the page cache along with swapping data out to disk to make available more memory as needed.

Buffers are in-memory block I/O buffers. They are relatively short-lived. Prior to Linux kernel version 2.4, Linux had separate page and buffer caches. Since 2.4, the page and buffer cache are unified and Buffers is raw disk blocks not represented in the page cache—i.e., not file data. The Buffers metric is thus of minimal importance. On most systems, Buffers is often only tens of megabytes.

Solution 3:

"Buffers" represent how much portion of RAM is dedicated to cache disk blocks. "Cached" is similar like "Buffers", only this time it caches pages from file reading.

quote from:

• https://web.archive.org/web/20110207101856/http://www.linuxforums.org/articles/using-top-more-efficiently_89.html