Shulou(Shulou.com)05/31 Report--

Today, the editor will share with you the relevant knowledge points about how to configure the basic memory pool initialization in Nginx. The content is detailed and the logic is clear. I believe most people still know too much about this knowledge, so share this article for your reference. I hope you can get something after reading this article.

Initialization of ngx_cycle

In the whole initialization process, the most important thing is the initialization of the global variable nginx_cycle. Many variables are initialized in this process.

Nginx_cycle is initialized by two local variables, init_cycle and cycle.

In fact, log initialization can also be regarded as initialization of nginx_cyle, because what happens next in the code is an assignment.

Ngx_memzero (& init_cycle, sizeof (ngx_cycle_t)); init_cycle.log = log;ngx_cycle = & init_cycle;// create memory pool 1kbinit_cycle.pool = ngx_create_pool (1024, log); if (init_cycle.pool = = null) {return 1;} / Save call parameters to global variables, init_cycle is only used to provide log parameters if (ngx_save_argv (& init_cycle, argc, argv)! = ngx_ok) {return 1 } / / Save configuration file path, program running path, call parameters to init_cycleif (ngx_process_options (& init_cycle)! = ngx_ok) {return 1;} / / get operating system information, cpu information, maximum number of connections, support for non-blocking connections and other if (ngx_os_init (log)! = ngx_ok) {return 1 } / * * ngx_crc32_table_init () requires ngx_cacheline_size set in ngx_os_init () * / / an alignment check table if (ngx_crc32_table_init ()! = ngx_ok) {return 1;} / / get information about all inherited connection fd if (ngx_add_inherited_sockets (& init_cycle)! = ngx_ok) {return 1;}

Memory pool

Nginx manages resources through centralized resource management, that is, opening all soon-to-be-used resources for access at any time, whether files or memory

The advantage of this is that it avoids the performance consumption caused by each creation and opening of resources.

Therefore, there is a memory pool module, which is used to centrally apply for memory resources and manage and allocate memory resources.

Memory pool structure:

/ / struct ngx_pool_data_t// memory pool block structure {{typedef struct {u_char * last; / / end location of current memory allocation u_char * end; / / end location of memory pool ngx_pool_t * next; / / next memory pool ngx_uint_t failed; / / memory allocation failure count} ngx_pool_data_t / / struct ngx_pool_s// memory pool structure {{struct ngx_pool_s {memory d; / memory pool block size_t max; / / memory to be allocated ngx_pool_t * current; / / points to the current memory pool start location ngx_chain_t * chain; ngx_pool_large_t * large / / point to ngx_pool_cleanup_t * cleanup; / / destructor ngx_log_t * log; / / log related to memory allocation}; / /}}

In this function, an encapsulated function ngx_memalign is used, which encapsulates the function of allocating memory according to data alignment in the system, which is implemented in different ways in different systems. Through macro definition, the adaptation of the operating system is realized, which is a beautiful skill.

# if (ngx_have_posix_memalign) / / void * ngx_memalign (size_t alignment, size_t size, ngx_log_t * log) / / memory allocation {{void * ngx_memalign (size_t alignment, size_t size, ngx_log_t * log) {void * p; int err; / / size units are byte instead of bit err = posix_memalign (& p, alignment, size) If (err) {ngx_log_error (ngx_log_emerg, log, err, "posix_memalign (% uz,% uz) failed", alignment, size); p = null;} ngx_log_debug3 (ngx_log_debug_alloc, log, 0, "posix_memalign:% p:%uz @% uz", p, size, alignment); return p } / /}} # elif (ngx_have_memalign) / / void * ngx_memalign (size_t alignment, size_t size, ngx_log_t * log) / / memory allocation using data alignment {{void * ngx_memalign (size_t alignment, size_t size, ngx_log_t * log)

The encapsulation of all system call functions related to memory allocation is defined in the ngx_alloc.c file

Posix_memalign system call is used here, and the memory allocated by this system call is aligned by default according to the size of the second parameter, so that when reading and writing data, cpu can read and write the whole block of data periodically, which greatly saves cpu time.

The memory allocated by this system call also exists in heap memory and can be freed using the free function, but the memory allocated by malloc is also aligned by default, and its only advantage over malloc is that it can specify the default alignment size.

Function completes the preliminary allocation of the memory pool, and takes the value of pool after execution:

$23 = (ngx_pool_t *) 0x80fe9f0 (gdb) p * init_cycle.pool$24 = {d = {last = 0x80fea18, end = 0x80fedf0, next = 0x0, failed = 0}, max = 984, current = 0x80fe9f0, chain = 0x0, large = 0x0, cleanup = 0x0, log = 0x80e3020}

As shown in the following figure:

These are all the contents of the article "how to configure basic memory Pool initialization in Nginx". Thank you for reading! I believe you will gain a lot after reading this article. The editor will update different knowledge for you every day. If you want to learn more knowledge, please pay attention to the industry information channel.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.