mmap mindmap

Access to files on disk, you must consolidate and move files into memory according to certain rules, and then access this file. The order in which the pages of the files to be accessed are arranged intoRadix tree. Assuming that the file is small and there is no memory writeback and access to the entire file, the logically linear organization of this file page is in memoryhas been transformed into a tree-like arrangement--radix tree (which is very important). But the actual

, this will improve performance, but will reduce performance. Let's put this problem in the first place.Some people say that I do not want to fwrite+fflush this combination, I want to write directly to page cache. This is our common file IO call read/write function.These functions are basically a function that corresponds to a system call, such as Sys_read/sys_write. The write function is called to copy data from the application layer to the kernel layer directly from the system call, copying fr

When writing a device driver, if you want to map the device memory to the user space, you need to implement MMAP. by reading the ldd3 introduction above, you have a little understanding of MMAP implementation. This article describes how to use Int remap_pfn_range (struct vm_area_struct * VMA, unsigned long effec_addr, Unsigned long PFN, unsigned long size, pgprot_t prot) function or Int io_remap_page_range

Solemnly declare: This article is written by the author based on my personal understanding. errors are inevitable. Please be prepared! You can reprint, modify, and indicate the source when reprinting! When you run sudo apt-Get update, the system prompts: E: Dynamic MMAP has no space. Increase the size of APT: cache-limit. Current Value: 25165824. (MAN 5 apt. conf), E: Error Handling libsvg-ruby1.8 (newfilever1), E: Problem with mergelist/var/lib/AP

1. An error is reported when ORACLE software is installed to 86%. The figure is missing. The log is as follows: /Oracle/u01/app/oracle/product/11.2.0/INFO: db_1/lib/sysliblist '-R/opt/SUNWcluster/lib-R/export/home/oracle/u01/app/oracle/product/11.2.0/db_1/lib-R/opt /ORCLcluster/lib/-y p, :/opt/SUNWcluster/lib:/opt/ORCLcluster/lib/:/usr/ccs/lib/amd64: /usr/lib/amd64-Qy-lm/export/home/oracle/u01/app/oracle/product/11.2.0/db_1/lib/prod/lib/amd64/crtn. o-lpthread INFO: ld: fatal:

"Dynamic MMap has no space. Please increase the resolution of APT: Cache-Limit... ". when updating the software in javastun, the following error occurs: Java code jiyj @ ubuntu :~ $ Sudo apt-get install firefox [sudo] password for jiyj: Sorry, try again. [sudo] password for jiyj: www.2cto.com is reading the package list... An error occurred! E: Dynamic MMap has no space. Increase the size of APT: Cache-Limi

Best references: 1. Master from the Internet. 2. UNP V2 posix ipc chapter 12. 3. Linux man command. Article 1: MMAP function Purpose 1. Map common files to the process memory space for memory ing Io. 2. Map special files to the process memory space for anonymous memory ing Io. 3. Map shm_open to open the POSIX shared memory zone to the memory space of the process, which can provide data sharing and IO among unrelated processes. # Include V

The video application can apply for a buffer from the v4l2 driver in two ways. 1. userptr, as the name implies, refers to the user space pointer. the application layer allocates the required memory space and passes it to the v4l2 driver layer as a pointer, the v4l2 driver saves the content of capture to the space indicated by the pointer. In general, the application layer needs to ensure that the memory space is physically consecutive (the IPU processing unit is required), and the Android syst

(n_buffers = 0; n_buffers {Struct v4l2_buffer Buf; // one frame in the driverClear (BUF );Buf. type = v4l2_buf_type_video_capture;Buf. Memory = v4l2_memory_mmap;Buf. Index = n_buffers; If (-1 = IOCTL (FD, vidioc_querybuf, BUF) // map the user spacePrintf ("vidioc_querybuf error \ n "); Buffers [n_buffers]. Length = Buf. length;Buffers [n_buffers]. Start =MMAP (null/* start anywhere */, // establishes a ing through MMAPBuf. length,Prot_read | prot_wr

Copy_to_user needs to check the validity of the pointer during each copy, that is, the pointer to the address of the user space is indeed the address of the process itself, instead of pointing to the location that does not belong to it, in addition, data is copied once each time, and memory is frequently accessed. Because the virtual address is continuous, the physical address may not necessarily be consecutive, resulting in frequent cache failures of the CPU, thus reducing the speed.MMAP only c

Dynamically passes the physical address and size of the kernel space to user space. This article also demonstrates two common methods that can be used for communication between kernel space and user space: Proc file system and Mmap shared memory.The entire kernel module, when the module inserts, establishes the proc file, allocates the memory. When the module is unloaded, the content written by the user space is printed.Here is the code for the kernel

View MySQL LogsInnodb:initializing buffer pool, size =128.0MInnodb:mmap (137363456bytes) failed; Errno Ainnodb:completed Initialization of buffer poolinnodb:fatal Error:cannot allocate memory forThe buffer Pool[error] Plugin'InnoDB'Initfunctionreturned error. [ERROR] Plugin'InnoDB'registration as a STORAGE ENGINE failed. [ERROR] Unknown/Unsupported storage engine:innodb[error] abortingToo few caches. free-m total used free shared buffers Cachedmem: 11

I. overview memory ing: in short, you can map a memory area of your space to the kernel space. After the ing is successful, your modifications to this memory area can be directly reflected in the kernel space. On the contrary, modifications made to

Recently in doing video output related things, for reserved for framebuffer memory use is not very clear, now find some information to tidy up, in case of use.For a system, there will be a lot of peripherals, then the management of these peripherals

Overview of Shared memory The shared memory area is the fastest form of IPC, where data delivery is no longer related to the kernel, in other words, processes no longer pass data to each other by executing system calls into the kernel. That is,

Shared memory can be said to be the most useful interprocess communication and the fastest form of IPC because processes can read and write directly to memory without requiring any copy of the data. For communication like pipelines and Message

I. overview memory ing: in short, you can map a memory area of your space to the kernel space. after the ING is successful, your modifications to this memory area can be directly reflected in the kernel space. On the contrary, modifications made to

    Ffi = require 'ffi' ffi. cdef [[ int open (const char * file, int flag); void * mmap (void * _ addr, int _ len, int _ prot, int _ flags, int _ fd, int _ offset); # pragma pack (1) typedef struct { char name [21]; unsigned short age;

Note: This example uses the form of shared file ing. The write end writes data and the read end reads data. Write end: /*-------------map_normalfile1.c-----------*/#include #include #include #include #include #include typedef struct{ char name[4];

is new communication, the shared memory area is re-established. Instead, keep the shared area until the communication is complete. In this way, the data content is stored in the shared memory and not written back to the file. The content in the shared memory is often written back to the file when the ing is removed. Therefore, the efficiency of communication with shared memory is very high. Linux 2.2.x kernel supports multiple memory sharing modes, such as