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memory management

This is a mind map about memory management. The main contents include: swapping and overwriting, continuous allocation storage management method, program loading and linking, and memory hierarchy.

Edited at 2024-10-24 00:28:27

JackTyler·881

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memory management

JackTyler·881

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memory management

memory hierarchy

CPU internal storage unit

Fastest access

Used to store temporary data and intermediate results

Cache

Located between CPU and main memory

Used to reduce the latency of CPU access to main memory

Divided into different levels such as L1, L2, L3 etc.

Main memory (RAM)

random access memory

Used to store operating systems, applications and data

Volatile storage, data is lost after power outage

Auxiliary storage (hard disk, SSD)

non-volatile storage

For long-term storage of data and programs

Slower than main memory, larger capacity

disk cache

Program loading and linking

Program compilation

precompiled

Processing preprocessing directives

compile

Translate preprocessed files into assembly language

compilation

Convert assembly language into machine language and generate target code

Program link

link process

Link the compiled object module and the required library functions together to form a total load module

Link method

static link

definition

Before running the program, link each target module and required library functions into a complete load module, which will not be disassembled later.

Features

The resulting executable is larger, but runs without additional loading and linking steps.

advantage

Improve program execution speed and reduce compatibility

Dynamic linking on load

definition

When the program is loaded into memory, it is linked while loading. That is, when an external module is found to be called, the module is immediately loaded and linked.

Features

Facilitates modification and updating of modules in the program without reopening the entire loaded module.

Dynamic linking at runtime‌

definition

Links to certain target modules are only performed when the module is needed during program execution.

Features

Memory space can be saved because only the currently needed modules are loaded.

Program loading

absolute mount mode

Definition‌: At compile time, if the specific location in memory where the program will reside is known, the compiler will produce object code with an absolute address.

Features‌: The logical address in the program is exactly the same as the actual memory address, without address conversion.

Applicable scenarios‌: single-program environment, memory usage is simple and clear.

Relocatable load mode

Definition‌: Load the load module into the appropriate location in memory, and relocate (i.e. modify) the address in the module when loading.

‌Features‌: Allows the program to be loaded into any location in the memory, but the address is fixed when loading and cannot be moved during operation.

‌Applicable scenarios‌: Multi-programming environment, where the final location of the program loaded into memory cannot be predicted during compilation.

Dynamic runtime loading mode‌

‌Definition‌: After the program is loaded into the memory, the address translation is not performed immediately, but the address translation is performed when the program is actually executed.

Features‌: Allows the program's location in memory to dynamically change, requiring the support of a relocation register.

Applicable scenarios‌: Scenarios that require programs to move frequently in memory, such as systems that support the swap function.

Address binding and memory protection

logical address

physical address

memory protection

Continuous allocation storage management method

definition

Allocate a contiguous memory space to the user process to ensure that the logical addresses in the program are also adjacent in physical memory.

Main distribution methods

single contiguous allocation

‌Features‌: The simplest memory management method, suitable for single-programming environments. The memory is divided into system area and user area. The user area has only a separate partition for user programs to use.

Advantages and Disadvantages‌: Advantages: Simple and easy to implement, no external debris. Disadvantages: It can only be used in single-user, single-task operating systems, with low memory utilization and large internal fragmentation.

Fixed partition allocation

Memory partitioning

Divide the user memory space into several fixed-size partitions. Only one job can be mounted per partition.

Partition size

Equal size: suitable for controlling multiple identical objects, but lacks flexibility. Different sizes: improve flexibility and divide into multiple small partitions, an appropriate number of medium partitions, and a small number of large partitions.

Advantages and Disadvantages

Advantages: Can be used in multiprogramming systems, no external fragmentation. Disadvantages: Large internal fragmentation, low storage space utilization, and lack of flexibility.

Dynamic partition allocation

Advantages and Disadvantages

Advantages and Disadvantages‌: Advantages: Improved memory utilization and high flexibility. Disadvantages: prone to external fragmentation and requiring complex memory management strategies.

Swapping and overwriting

swap

Definition‌: Swap usually refers to the exchange of positions or states between two or more elements.

characteristic: Bidirectionality: An exchange involves movement or change in two directions. Reversibility: The swapped state can be restored to the original state by swapping again.

cover

Definition‌: Covering means that one element or set is replaced or obscured by another element or set.

characteristic: Unidirectionality: Overwriting is usually a one-way process, where a new element or collection replaces an old one. Irreversibility: Once overwriting occurs, the original state may not be fully restored.