The above process is easier said than done. Some memory is allocated and recycled statically in advance, while others are dynamically allocated and recycled on demand. From the above, we can see that the address that the process can operate directly is virtual address. truncate range of pages specified by start & end byte offsets, — Vmalloc allocated kernel virtual memory and kmalloc / get_ free_ The kernel virtual memory allocated by page is located in different intervals and does not overlap. When users execute MMAP system call, this method will be called to access memory through file. Here is a small program to help you recognize the above several distribution functions corresponding to the region. Along with this clue, the main problems we have studied focus on the following issues. Many device drivers use memory mapping function to associate a segment of address in user space to device memory. Haven’t you heard of the architecture yet? The driver is responsible for mapping a certain length of kernel virtual address (allocated by vmalloc) to the device file. The following steps are required for the transformation: a) Find the page table corresponding to vmalloc virtual memory, and find the corresponding page table entry. Our example here hopes to use memory mapping to map a part of virtual memory in the system kernel to user space for application to read. MMU translates physical memory addresses to linear addresses used by the operating system, and requests a page fault interrupt, when the CPU tries to access memory that it is not entitled to. Therefore, vmalloc must update the kernel page table when allocating kernel virtual address, while kmalloc or get_ free_ Page does not need to update the kernel page table because of the contiguous memory allocated. called when min_free_kbytes changes or when memory is hot-{added|removed}, — For example, memory used in DMA transmission must be allocated continuously because it does not involve page mechanism. Its basic function is to manage the memory hierarchy of RAM and secondary memory devices. release old fs-specific metadata on a page, — truncate *all* the pages from an offset, — However, the management methods of these memories are different due to different memory uses. As a result, you can see the content of the kernel virtual address (OK! The user process can only access the virtual address of user space, but not the virtual address of kernel space. The situation here is very similar to the virtual memory allocated by user space. O module, see makefile for specific parameters, 1 find map under / proc / devices_ Device name and device number of driver: grep mapdrv / proc / devices, 2 create device file mknod mapfile C 254 0 (in my system, the device number is 254). map an array of pages into virtually contiguous space, — If you want to see the memory area occupied by a process, you can get it by using the command cat / proc / < PID > / maps (PID is the process number, you can run the example given above -. Memory management services in Li… Memory management has always been the focus of all operating system books, whether on the market or online are full of a large number of teaching materials and materials related to memory management. The method or scheme of managing memory depends upon its hardware design. On this basis, it gradually goes deep into the kernel to discuss the system physical memory management and the use of kernel memory. Add an arbitrary waiter to a page's wait queue, — You should know that the address in the physical memory mapping area corresponds to the kernel page table in an orderly manner. But in either case, do_ The mmap() function adds an address range to the process’s address space whether it’s expanding an existing memory area or creating a new one. — b) Gets the page pointer corresponding to the page table entry, c) Get the corresponding address of the kernel physical memory mapping area through the page。. — But these data are static statistics of program compilation, and the above shows the dynamic values of process runtime, but the two are corresponding. read into page cache, using specified page allocation flags. For a better understanding of the request page mechanism, take a look at the Book Understanding the Linux kernel in depth. mentioned above. In order to meet the needs of internal check, a technology called slab allocator is adopted in Linux system. map pages linearly into kernel virtual address (vmalloc space), — For example, if you execute the size example, you will get. The data format of each row is as follows: (memory area) start end access rights offset primary device number: secondary device number I node file. The benefit of the request page is to save the free memory and improve the system throughput. 2. Our example program will demonstrate the whole process of mapping the kernel virtual address allocated by vmalloc to the user address space. Each vmalloc allocated kernel virtual memory corresponds to a VM_ Struct structure (May and VM_ area_ Different kernel virtual addresses are separated by 4K free area to prevent cross boundary. Let’s take a look at the conversion relationship between the process address space and the physical page by borrowing a picture from the Linux device driver. — find the next hole (not-present entry), — — Return number of page frames in holes within a range, — We use a small example (the original form is taken from user level memory management) to show the differences and locations of various memory areas mentioned above. - tries to allocate given range of pages, — destroys a pool of dma memory blocks. In this sense, we can think of the stack as a memory area to store and exchange temporary data.
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