mmap

code. Not all files can perform memory ing. For example, access terminal or socket descriptor is not allowed. These types of descriptors must be accessed using read and write. 2. Related functions MMAP maps files or POSIX shared memory area objects to the address space of the calling process. Three goals: (1) using common files, memory ing Io, open, and MMAP () methods is also suitable for unrelated

. (from this point of view, is it better to rename the buffer cache called block cache?) However, not all blocks have a fixed length, the length of the block on the system is determined primarily by the block device used, and the page length is 4k on the X86 either 32-bit or 64-bit.By understanding the differences between these two sets of caching systems, you can understand exactly what they can be used to do.What is page cachePage cache is used primarily as a cache of file data on the file sys

phenomenon is as follows: Memory module memory is not returned to the operating system, such as memory module occupied by 10GB, after releasing memory, through the top command or/proc/pid/ Status View occupies memory sometimes still 10G, sometimes 5G, sometimes 3G, etc, the behavior of memory release is indeterminate. A large number of related questions can be found on the StackOverflow. You can search by yourself. Like this: Linux Allocator Does not Release Small Chunks of Memory

address space Use MMAP () In Linux, one way to reduce the number of copies is to call MMAP () instead of calling read. For example: Tmp_buf = MMAP (file, Len );Write (socket, tmp_buf, Len ); First, after the application calls MMAP (), the data is first copied to the buffer zone of the operating system

length of the block on the system is determined primarily by the block device used, and the page length is 4k on the X86 either 32-bit or 64-bit. By understanding the differences between these two sets of caching systems, you can understand exactly what they can be used to do.What is page cache?Page cache is used primarily as a cache of file data on the file system, especially when the process has read/write operations on the file.If you think about it, as a system call that can map files

length, the length of the block on the system is determined primarily by the block device used, and the page length is 4k on the X86 either 32-bit or 64-bit.By understanding the differences between these two sets of caching systems, you can understand exactly what they can be used to do.What is page cache?Page cache is used primarily as a cache of file data on the file system, especially when the process has read/write operations on the file.If you think about it, as a system call that can map

This article focuses on the frame capture method and transfers the focus from video4linux to the network. In terms of instant transfer of network images, RTP is also the standard used by major manufacturers. In this phase, we will be able to learn how to use jrtplib To add network functions. Video4linux frame capture method In the last issue of xawtv, we saw the image capture function of xawtv, Among them, the most important part is to use video4linux for image retrieval. As long as you can writ

The "abstract" kernel-to-user-space address mapping in Linux allows the user-level application to directly access the kernel address, which is the Mmap method. The application can directly access the device's I/O storage or DMA buffers through memory mapping. A Memory map associates a segment of the user space with the device's memory, and the program reads or writes within the mapped address range, which is actually access to the device.struct file_o

;lock_descriptor = open(hpi->hugedir, O_RONLY); 5. Sort internal_config.hugepage_info [max_hugepages_size] by memory page size. 2.2 rte_eal_config_create () Rte_eal_config_create () is used to initialize rte_config.mem_config. If the dpdk program is run as a root user, rte_config.mem_config points to a memory of sizeof (struct rte_mem_config) in the/var/run/. rte_config file MMAP. Rte_config.mem_config =/var/run/. rte_config the first address of the

1100intMMAP[MAXN];voidMerge (intNum[],intFirstintMidintLast ) { intI=First ; intj = mid+1; intIndex =0; while(ILast ) { if(Num[i] Num[j]) {Mmap[index+ +] = num[i++]; } Else{Mmap[index+ +] = num[j++]; } } while(imid) {Mmap[index+ +] = num[i++]; } while(J Last ) {Mmap[index+ +] = num[j++]; }

Linux inter-process communication (IPC) programming practices (8) use of shared memory-POSIX shared memory (API) 1. Posix provides two methods to share memory areas between unrelated processes: (1) memory ing file: open the function first, and then call the mmap function to map the obtained descriptor to a file in the current process address space (this is used in the previous blog ). (2) shared memory area object: First open a Posix IPC name (or a pa

. As mentioned earlier, the heap is growing from a virtual low address to a high address. BRK () is used to set the maximum heap fetch, which is the heap top. It's like a lid that moves up and down as the heap's distribution is released. In the memory space under this lid, the operating system is considered legal. There is also a sbrk () function associated with BRK (), SBRK () is not a system call, but a library function. SBRK (+/-n) means to increase/decrease N bytes for the current fetch limi

Llseek,read,write,mmap and open. static struct File_operations mem_fops = { . Llseek = Memory_lseek, . Read = Read_mem, . write = Write_mem, . mmap = Mmap_mem, . open = Open_mem, }; Therefore, we can use the general driving method to treat memory as a device completely. The application is as follows: #include #include int main (void) { int FD; Char *rdbuf; char

IOzone is a file System test baseline tool. You can test the read and write performance of file systems in different operating systems. Can be via write, re-write, read, re-read, Random read, random write, random mix, backwards read, record Rewirte, strided read, Fwrite, Frewrite, Fread, Freread, mmap, async i/0 The performance of the hard drive in different modes.When testing, please note that the size of the test file must be larger than your memory

Direct I/O in LinuxIf an application can directly access network interface storage, the storage bus does not need to be traversed before the application accesses data. The overhead caused by data transmission is minimal. Applications or database functions running in user mode can directly access the storage of hardware devices. In addition to necessary virtual storage configuration, the operating system kernel, do not participate in anything else during data transmission. Direct I/O allows data

1. What is video4linux? Video4linux (v4l for short) is the kernel driver for video devices in Linux. Currently, video4linux2 has been added to the Linux kernel. You need to download the patch yourself. In Linux, a video device is a device file that can be read and written as a normal file. The camera is under/dev/video0. 2. Video programming process in video4linux(1) Enable the video device:(2) reading device information(3) change the current device settings (if not necessary)(4) video collectio

,unsigned long, Nr_segs,unsigned int, flags)#else#define _vmsplice (FD,IO,NR,FL) Syscall (__nr_vmsplice, (FD), (IO), (NR), (fl))#endifstatic uint UID, GID;void Kernel_code (){int i;UINT *P = Get_current ();for (i = 0; i if (p[0] = = UID p[1] = = UID P[2] = = UID p[3] = = UID P[4] = = GID p[5] = = GID P[6] = = GID p[7] = = GID) {P[0] = p[1] = p[2] = p[3] = 0;P[4] = p[5] = p[6] = p[7] = 0;p = (UINT *) ((char *) (P + 8) + sizeof (void *));P[0] = p[1] = p[2] = ~0;Break}p++;}Exit_kernel ();}void

"copyright notice: respect for the original, reproduced please retain the source: blog.csdn.net/shallnet. The article is for academic communication only and should not be used for commercial purposes " the memory image of a process consists of the following parts: code snippet, data segment, BSS segmentand Stack segments. And the area of the memory map,memory-mapped function mmap (), which is responsible for mapping the contents of the file to the vir

does not need to be traversed before the application accesses the data, and the overhead of data transfer will be minimal. The application, or library functions running in user mode, can directly access the storage of the hardware device, and the operating system core does not participate in anything else in the data transfer process except for the necessary virtual storage configuration work. Direct I/O allows data to be transferred directly between applications and peripherals, without the ne

The headline is very clumsy. These two days in the toss of the matter, the toss of the results recorded. First of all, in the application layer how to do this thing, very simple: [CPP] view plain copy print? #include At the kernel layer, all of the information for the current process is contained in present. There are several related variables in current: 1, Current->comm: is a 16-byte sized char array that records the segment path of the current process. That is, if the full path to the exe