一个详细介绍CPU & Memory & Kernel的博客

本文探讨了软件插图在现代设计中的应用趋势,包括如何使用插图增强用户体验,提高软件产品的吸引力,并提供了几种流行的软件插图风格和创作技巧。
### Kernel Dynamic Memory Management Allocation and Deallocation Techniques Kernel dynamic memory management involves the allocation and deallocation of memory in the kernel space, which is critical for the efficient operation of operating systems. The techniques used are designed to manage memory efficiently while minimizing fragmentation and ensuring timely allocation and deallocation. #### Allocation Techniques 1. **Buddy System**: This technique divides memory into blocks that are powers of two. When a request for memory is made, the system finds the smallest block that can satisfy the request. If the block is too large, it is split into smaller blocks until the appropriate size is reached. This method helps reduce fragmentation but can lead to internal fragmentation if the requested sizes do not align well with the power-of-two sizes [^1]. 2. **Slab Allocation**: Slab allocation is designed to improve performance by preallocating chunks of memory (slabs) for specific data structures. Each slab contains multiple objects of the same type and size. This reduces the overhead associated with allocating and deallocating memory for frequently used data structures, such as inodes or file descriptors [^1]. 3. **Zone-Based Allocation**: Memory is divided into zones based on physical addresses. Different zones may have different characteristics, such as DMA-capable memory or high-memory regions. This allows the kernel to allocate memory that meets specific hardware requirements [^1]. 4. **Per-CPU Caches**: To reduce contention and improve performance on multi-processor systems, per-CPU caches are used. These caches store recently freed memory objects, allowing them to be quickly reused without the need for global locks [^1]. #### Deallocation Techniques 1. **Reference Counting**: Objects in memory often maintain a reference count indicating how many parts of the system are using them. When an object's reference count drops to zero, it is safe to deallocate the memory [^1]. 2. **Garbage Collection**: While not commonly used in kernel space due to real-time constraints, some systems implement limited forms of garbage collection. Region-based memory management can help track and release memory that is no longer needed [^3]. 3. **Deferred Freeing**: In some cases, memory is not immediately returned to the free pool upon deallocation. Instead, it is placed in a deferred freeing queue, where it can be processed asynchronously to avoid blocking the current execution context [^1]. 4. **Memory Compaction**: Over time, memory fragmentation can become an issue. Memory compaction involves moving allocated pages to consolidate free space, making larger contiguous blocks available for allocation [^1]. ### Example Code: Simple Slab Allocator The following example demonstrates a simple slab allocator implementation in C: ```c #include <stdio.h> #include <stdlib.h> #include <string.h> #define SLAB_SIZE 1024 #define OBJECT_SIZE 32 typedef struct { void* memory; int num_objects; int free_count; void** free_list; } Slab; Slab* create_slab(int num_objects) { Slab* slab = (Slab*)malloc(sizeof(Slab)); if (!slab) return NULL; slab->memory = malloc(num_objects * OBJECT_SIZE); if (!slab->memory) { free(slab); return NULL; } slab->num_objects = num_objects; slab->free_count = num_objects; slab->free_list = (void**)malloc(num_objects * sizeof(void*)); if (!slab->free_list) { free(slab->memory); free(slab); return NULL; } for (int i = 0; i < num_objects; i++) { slab->free_list[i] = (char*)slab->memory + i * OBJECT_SIZE; } return slab; } void* allocate_object(Slab* slab) { if (slab->free_count == 0) return NULL; void* obj = slab->free_list[--slab->free_count]; return obj; } void free_object(Slab* slab, void* obj) { if (slab->free_count < slab->num_objects) { slab->free_list[slab->free_count++] = obj; } } void destroy_slab(Slab* slab) { free(slab->free_list); free(slab->memory); free(slab); } int main() { Slab* slab = create_slab(10); if (!slab) { printf("Failed to create slab\n"); return 1; } void* obj1 = allocate_object(slab); void* obj2 = allocate_object(slab); printf("Allocated objects: %p, %p\n", obj1, obj2); free_object(slab, obj1); free_object(slab, obj2); destroy_slab(slab); return 0; } ``` This code defines a simple slab allocator that manages a fixed number of objects of a specified size. It includes functions for creating a slab, allocating an object, freeing an object, and destroying the slab. ###
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