Linux+page+cache+里的几个函数的源码分析

page cache 在linux vfs 中是比较重要的一层，其功能就不详细介绍了。主要介绍了几个关键性函数，容易帮助了解page cache里的整体逻辑和流程先看一下page 的结构体

/*
* Each physical page in the system has a struct page associated with
* it to keep track of whatever it is we are using the page for at the
* moment. Note that we have no way to track which tasks are using
* a page.
*/
struct page {
unsigned long flags; /* Atomic flags, some possibly
* updated asynchronously */
atomic_t _count; /* Usage count, see below. */
atomic_t _mapcount; /* Count of ptes mapped in mms,
* to show when page is mapped
* & limit reverse map searches.
*/
union {
struct {
unsigned long private; /* Mapping-private opaque data:
* usually used for buffer_heads
* if PagePrivate set; used for
* swp_entry_t if PageSwapCache;
* indicates order in the buddy
* system if PG_buddy is set.
*/
struct address_space *mapping; /* If low bit clear, points to
* inode address_space, or NULL.
* If page mapped as anonymous
* memory, low bit is set, and
* it points to anon_vma object:
* see PAGE_MAPPING_ANON below.
*/
};
#if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
spinlock_t ptl;
#endif
};
pgoff_t index; /* Our offset within mapping. */
struct list_head lru; /* Pageout list, eg. active_list
* protected by zone->lru_lock ！
*/
/*
* On machines where all RAM is mapped into kernel address space,
* we can simply calculate the virtual address. On machines with
* highmem some memory is mapped into kernel virtual memory
* dynamically, so we need a place to store that address.
* Note that this field could be 16 bits on x86 ... ;）
*
* Architectures with slow multiplication can define
* WANT_PAGE_VIRTUAL in asm/page.h
*/
#if defined（WANT_PAGE_VIRTUAL）
void *virtual; /* Kernel virtual address （NULL if
not kmapped, ie. highmem） */
#endif /* WANT_PAGE_VIRTUAL */
};

page_cache_get（）主要是调用函数get_page

static inline void get_page（struct page *page）
{
if （unlikely（PageCompound（page）））
page = （struct page *）page_private（page）;
atomic_inc（&page->_count）;
}

主要page里的计数器+1，表示page引用的reference 次数 page_cache_release（）的核心函数 put_page_testzero

static inline int put_page_testzero（struct page *page）
{
BUG_ON（atomic_read（&page->_count） == 0）;
return atomic_dec_and_test（&page->_count）;
}

显然是page的计数器-1, page的引用被释放

Linux RAMDisk 源码分析Linux Tmpfs 源码分析相关资讯 Linux基础教程

Linux基础教程：对文件打包压缩（03月08日）
基础教程：Linux 新手应该知道的（09/06/2015 21:17:20）
Linux基础教程：find 与 xargs （04/05/2015 10:20:11）

Linux基础教程：tar 命令使用介绍（12/03/2015 13:19:47）
Linux基础教程（1）操作系统基础（08/15/2015 20:44:01）
Linux基础教程：从源码安装软件（04/05/2015 10:14:45）

本文评论查看全部评论（0）