深入理解linux内存管理之 页框管理结构page |
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物理内存被划分成固定大小的块，称为页帧，kernel会为每一个页帧都创建struct page管理结构，保存在全局数组mem_map中。 内核应该注意保持page结构尽量小，因为对于现代计算机，物理内存包含大量的页帧，即便是增加page一点点空间，都会导致保存所有页帧page结构多占用大量物理内存。 所以我们可以在page结构的设计中，看到为了减小page结构尺寸所做的努力。 struct page /* * 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, though if it is a pagecache page, rmap structures can tell us * who is mapping it. */ struct page { unsigned long flags; /* Atomic flags, some possibly * updated asynchronously */ atomic_t _count; /* Usage count, see below. */ union { atomic_t _mapcount; /* Count of ptes mapped in mms, * to show when page is mapped * & limit reverse map searches. */ struct { /* SLUB */ u16 inuse; u16 objects; }; }; 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 USE_SPLIT_PTLOCKS spinlock_t ptl; #endif struct kmem_cache *slab; /* SLUB: Pointer to slab */ struct page *first_page; /* Compound tail pages */ }; union { pgoff_t index; /* Our offset within mapping. */ void *freelist; /* SLUB: freelist req. slab lock */ }; struct list_head lru; /* Pageout list, eg. active_list * protected by zone->lru_lock ! */ /* * On machines where all RAM is mapped into ker |
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