What is mem in linux

In Linux, mem is physical memory; when the physical memory is about to overflow, the infrequently used memory in the memory will be transferred to SWAP, and will be transferred back after the physical memory is free and the SWAP memory is active.

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

What is mem in linux

mem is physical memory. When the physical memory is about to overflow, the infrequently used memory in the memory will be transferred to SWAP until the physical memory is free, and the swap memory Transfer it back after it becomes active

Linux mem/swap/buffers/cached difference

The free command provides a more concise view of system memory usage compared to top:

# free -m

mem: Indicates physical memory statistics

buff/cache: Indicates cache statistics of physical memory

swap: Indicates the usage of the swap partition on the hard disk

The currently available memory of the system is not marked by free in the first line. It only represents unallocated memory.

The buffer/cache column is too high

## What is the main purpose of #buff/cache?

Linux has an advanced caching mechanism, which will target dentry (used in VFS-virtual file system to accelerate the conversion of file path names to inodes), buffer cache (for reading and writing disk blocks) and page cache ( Perform caching operations for file inode reading and writing to improve reading and writing efficiency. However, after a large number of file operations are performed, the cache will basically use up the memory resources. Although the file reading efficiency is improved, the physical memory will be gradually used up.

It turns out that the system performs frequent file reading and writing operations, but why does the operating system not actively recycle? It turns out that the default parameter setting of drop_caches is not to release.

The value of drop_caches can be a number between 0-3, representing different meanings:

0: Do not release (system default value)

1: Release the page cache

2: Release dentries and inodes

3: Release all caches

Modification:

# echo 1 > /proc/sys/vm/drop_caches

Interlude

When Linux physics When the memory is about to be exhausted, the system will transfer the memory occupied by some processes to the swap area. When part of the physical memory is released, some memory occupation in the swap area slowly returns to the mem area, but the mem area is no longer the same as before. At full load, there is a part of free memory!

[Summary]

1) When the physical memory is almost exhausted, the system does not crash, but uses swap as temporary memory. When both are exhausted, the system OutofMemory

2) The physical memory reaches the peak, and the memory occupied by some uncommon processes in the system is mentioned in the swap area

3) When the resources in the Men area are released, the memory moved to the swap area does not Will all come back, and will slowly return to the men area as the system or program wakes up

4) swap is the memory virtualized by the disk when the memory is not enough. The disk is mainly an I/O level operation, and It is not a system kernel level operation, and the processing speed is not at the same level as the mem area

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