mmap

Because the project requires, you need to access the actual physical address in Linux userspace. i) User space can be accessed directly by opening the/DEV/MEM device file and then mmap () innuendo static int Read_type () { void * map_base; FILE *f; int type,fd; #define READ_REG32 (REG) (* (volatile int *) (reg)) #define alloc_size (1024) fd = open ("/ Dev/mem ", O_RDWR | O_sync); if (FD) { printf ("Success to Open/dev/mem fd=%08x\n", F

therefore do not occupy any disk space. (No call to malloc or mmap) Cached : The allocated page in the physical store is currently slow to exist. (already called malloc and Mmap, which is being referenced in the program) Not cached : the allocated pages in physical storage are not slow to exist. (already called malloc and mmap, not yet referenced in the program)

system in the source program compiled according to the nature of the information. [3] The page system address space is one-dimensional, that is, a single linear address space, the programmer can only use an identifier to represent an address. Segmentation of the job address space is two-dimensional, the programmer in the identification of an address, both the need to give the paragraph name, but also to give a paragraph within the address. (3) malloc under what circumstances to invoke

Enumv4l2_memory memory; V4l2_memory_mmap or V4l2_memory_userptr __u32 reserved[2]; }; Get and record the cached physical space Using Vidioc_reqbufs, we get the Req.count cache, the next step is to get the cached address by invoking the VIDIOC_QUERYBUF command, and then using the Mmap function to convert to an absolute address in the application, and finally putting this cache into the cache queue: typedef structvideobuffer{ Void*start; size_t length

some complexity. To reduce overhead, we can start by eliminating the duplication between the kernel buffer and the user buffer.One way to eliminate replication is to change the read system call to MMAP system calls, for example:Tmp_buf = mmap (file, Len);Write (socket, tmp_buf, Len);For a better understanding of the operation of this design, see Figure 2. The context-switching section is consistent with Fi

its cache if the memory is managed with page allocation. Of course, not all of the memory is managed by pages (page), and many are managed against blocks (block), which are used in buffer cache if the cache function is to be used. (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-b

1) Socket: Often encountered, not spoken2) Signal: Use Kill to send signals, Signal,settimer and other system calls can send a signal to another process, to achieve the purpose of inter-process communication.Kill (p1,16); / * Send interrupt signal to process number P1 process 16*/Signal (SIGINT,GO); / * After receiving the SIGINT signal, go to the GO function to process it * /3) Shared Memory: The use of mmap system calls to do the shared memory,

kernel module needs to include structUio_info {Char*name;Char*version;structUio_mem Mem[max_uio_maps];LongIrq UnsignedLongIrq_flags;void*priv; Irqreturn_t (*handler) (intIrqstructUio_info *dev_info);int(*mmap) (structUio_info *info,structVm_area_struct *VMA);int(*open) (structUio_info *info,structInode *inode);int(*release) (structUio_info *info,structInode *inode);/ * Internal Stuff omitted * /};In the structure above, name is the name of the device

The previous section described opening a memory-mapped file by the Open function, and then mapping the resulting descriptor to the current process address space by the MMAP function. This section describes another similar shared memory approach, where the Shm_open function opens a posix.1 IPC name (perhaps a path name in the filesystem), and the returned descriptor is mapped by the function mmap to the curr

Proc_none Page not accessible Flags Description Map_shared The change is shared Map_private The change is private. Map_fixed Explain the addr parameter exactly, and if you do not specify this parameter, it will be aligned with memory of 4 K size Map_anonymous Create an anonymous map area that does not involve files Mmap

the package name, you can use the PS command to get all the running programs, including the PID. Take your own browser for example: Copy Code code as follows: LIUHX@UC ~ $ adb shell Dumpsys meminfo com.android.browser Applications Memory Usage (KB): uptime:23140065 realtime:23140065 * * Meminfo in PID 939 [com.android.browser] * *Shared Private Heap Heap HeapPss Dirty Dirty Size Alloc Free------ ------ ------ ------ ------ ------Native 7111 748 7048 8964 8634 329Dalvik 7338 509

practical reference meaning of the three parameters of Virt, res and SHR in the top command. The last part introduces the format of the Smaps file, By analyzing the Smaps file we can learn more about the usage of process physical memory, such as how much space the Mmap file occupies, how much space is consumed by dynamic memory, how much space the function call stack consumes, and so on. Two concepts about memory To understand the output of the top c

text segment to not allow it to read or modify any kernel code and data structures that do not allow it to read or write to other processes that are not allowed to modify virtual pages that are shared with other processes unless all the sharer is shown to allow it to do so 5. Missing pages Interrupt process After a missing pages break, those operations are performed. When a process occurs with a missing fault, the process falls into the kernel state and performs the following actions: 1. C

Label:First, data persistence Diydb is a document-based database (not an in-memory database), and he needs to persist the data, and read and write data on disk. How is it more efficient to read and write data on disk? The current approach to Linux is to use Mmap, the memory-mapping mechanism. Why do you say mmap is efficient? We know that when we read a file in the process, it is generally necessary to firs

Lighting mdb (lmdb) is a high performance mmap KV database, basic introduction and documentation see Symas official website, this article will try to analyze its source code structure to understand the key technology of database design. This series of articles will attempt to analyze from the following aspects. System Architecture (This article) Mmap Mapping (series 2) B+tree operation (Se

void *mmap (void *addr,size_t len,int prot,int flags, int fd,off_t offset); Prot: Protection method Prot_read: Page readable Prot_write: Page writable Prot_exec: Prot_none: Fiags: Map_shared: Map_private: The change is private Map_fixed: Accurate explanation of addr Map_anonymous: Set up anonymous mappings, no files involved Mmap is to r

code.Char [] Maccode = {0x, 0x8b, 0x);The Maccode corresponding assembly instructions are:mov (%rdi),%raxIn fact, it can be seen that the machine code is bitstream, so it is not difficult to load it into memory. And the question is how it should be done.All right. Let's simulate the process of executing the newly generated machine code. Assuming that the JIT has compiled a new machine code for us, it is a machine code for the SUM function:Long (long num) {return1;} // the corresponding mac

normally call, the objects we create are assigned here, and bitmap are allocated directly on native, and the limit for memory is Native+dalvik cannot exceed the maximum limit.Use the following command to view the memory usage of the program:adb shell Dumpsys meminfo $package _name or $pid//Use the program's package name or process IDView memory usage of the Shrimp Music appadb shell Dumpsys meminfo fm.xiami.mainApplications Memory Usage (KB):uptime:71696500 realtime:98283758* * Meminfo in PID 1

(pthread_mutex_unlock (PM) = 0 );\ } While (0) [CPP] View plaincopyprint? Check_xh_lock (watch_mutex ); Check_xh_lock (request_mutex ); Check_xh_lock (reply_mutex ); Cout Xs_unwatch (pthis-> XH, pthis-> path. c_str (), map_path ("watch", pthis-> path). c_str ()); Check_xh_lock (watch_mutex ); Check_xh_lock (request_mutex ); Check_xh_lock (reply_mutex ); Cout Xs_close (pthis-> XH ); Pthis-> XH = 0; The test is as follows: [Plain] View plaincopyprint? Viktor @ buxiang-OptiP

I have already talked about how the kernel manages physical memory. But the fact is that the kernel is the core of the operating system, not only managing its own memory, but also managing the address space of the process. The Linux operating system uses the virtual memory technology. All processes share the memory in a virtual way. The process address space is composed of linear address zones in each process, and more importantly, the kernel allows the process to use the addresses in the space.