感谢支持
我们一直在努力

Linux平台上几个常见内核内存分配函数

  * kmalloc


  Prototype:


  #include <linux/slab.h>


  void *kmalloc(size_t size, int flags);


  Kmalloc分配一段未清0的连续物理内存页,并返回虚存地址。有点是快,并且可指定flag,如DMA内存,高地址区域内存等。缺点是不能分配大于128KB(处于跨平台考虑),几个重要的flag:


  GFP_ATOMIC


  Used to allocate memory from interrupt handlers and other code outside of a process context. Never sleeps.


  GFP_KERNEL


  Normal allocation of kernel memory. May sleep.


  GFP_USER


  Used to allocate memory for user-space pages; it may sleep.


  GFP_HIGHUSER


  Like GFP_USER, but allocates from high memory, if any. High memory is described in the next subsection.


  * slab allocator(lookaside cache)


  从Memcached的实现知道有这么一个内存管理策略,其显着特点是分配一组相同大小的内存块作为内存池,其实现对应于源代码中的<linux/slab.h>和mm/slab.c。


  Prototype:


  #include <linux/malloc.h>


  kmem_cache_t *kmem_cache_create(char *name, size_t size, size_t offset,


  unsigned long flags, constructor( ), destructor( ));


  int kmem_cache_destroy(kmem_cache_t *cache);


  /proc/slabinfo


  A virtual file containing statistics on slab cache usage.


  *__get_free_pages


  Prototype:


  _ _get_free_pages(unsigned int flags, unsigned int order);

  返回2^order个未清0连续物理页面,flags与kmalloc中flags一致,允许的最大order值为10或者11(根据体系结构不同)


  *alloc_pages


  Prototype:


  struct page *alloc_pages_node(int nid, unsigned int flags,


  unsigned int order);


  Kernel中页分配器实现,__get_free_pages即调用alloc_pages实现的


  The real core of the Linux page allocator is a function called alloc_pages_node:


  *vmalloc


  分配地址连续虚存,而不保证物理地址连续,大部分情况下适合“软件”,而不是驱动程序。相对而言,kmalloc和__get_free_pages虚存map到物理内存只需要增减一个偏移,而使用vmalloc分配需要修改页表,故vmalloc的开销较大,分配少数几个页面的效率太低。


  *per-cpu variables


  Each cpu hold an independant copy in their respective processor’s caches, so there is no lock required and improve better performance, implemented as a linux 2.6 feature. Defined in <linux/percpu.h>.


  DEFINE_PER_CPU(type, name);


  get_cpu_var(sockets_in_use)++;


  put_cpu_var(sockets_in_use);

赞(0) 打赏
转载请注明出处:服务器评测 » Linux平台上几个常见内核内存分配函数
分享到: 更多 (0)

听说打赏我的人,都进福布斯排行榜啦!

支付宝扫一扫打赏

微信扫一扫打赏