mirror of
https://github.com/gatieme/LDD-LinuxDeviceDrivers.git
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297 lines
12 KiB
C
297 lines
12 KiB
C
enum zone_type {
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#ifdef CONFIG_ZONE_DMA
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/*
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* ZONE_DMA is used when there are devices that are not able
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* to do DMA to all of addressable memory (ZONE_NORMAL). Then we
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* carve out the portion of memory that is needed for these devices.
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* The range is arch specific.
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*
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* Some examples
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*
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* Architecture Limit
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* ---------------------------
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* parisc, ia64, sparc <4G
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* s390 <2G
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* arm Various
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* alpha Unlimited or 0-16MB.
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*
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* i386, x86_64 and multiple other arches
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* <16M.
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*/
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ZONE_DMA,
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#endif
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#ifdef CONFIG_ZONE_DMA32
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/*
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* x86_64 needs two ZONE_DMAs because it supports devices that are
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* only able to do DMA to the lower 16M but also 32 bit devices that
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* can only do DMA areas below 4G.
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*/
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ZONE_DMA32,
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#endif
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/*
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* Normal addressable memory is in ZONE_NORMAL. DMA operations can be
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* performed on pages in ZONE_NORMAL if the DMA devices support
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* transfers to all addressable memory.
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*/
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ZONE_NORMAL,
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#ifdef CONFIG_HIGHMEM
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/*
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* A memory area that is only addressable by the kernel through
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* mapping portions into its own address space. This is for example
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* used by i386 to allow the kernel to address the memory beyond
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* 900MB. The kernel will set up special mappings (page
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* table entries on i386) for each page that the kernel needs to
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* access.
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*/
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ZONE_HIGHMEM,
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#endif
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ZONE_MOVABLE,
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#ifdef CONFIG_ZONE_DEVICE
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ZONE_DEVICE,
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#endif
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__MAX_NR_ZONES
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};
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struct zone {
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/* Read-mostly fields */
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/* zone watermarks, access with *_wmark_pages(zone) macros */
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unsigned long watermark[NR_WMARK];
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unsigned long nr_reserved_highatomic;
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/*
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* We don't know if the memory that we're going to allocate will be
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* freeable or/and it will be released eventually, so to avoid totally
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* wasting several GB of ram we must reserve some of the lower zone
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* memory (otherwise we risk to run OOM on the lower zones despite
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* there being tons of freeable ram on the higher zones). This array is
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* recalculated at runtime if the sysctl_lowmem_reserve_ratio sysctl
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* changes.
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* 分别为各种内存域指定了若干页
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* 用于一些无论如何都不能失败的关键性内存分配。
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*/
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long lowmem_reserve[MAX_NR_ZONES];
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#ifdef CONFIG_NUMA
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int node;
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#endif
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/*
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* The target ratio of ACTIVE_ANON to INACTIVE_ANON pages on
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* this zone's LRU. Maintained by the pageout code.
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* 不活动页的比例,
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* 接着是一些很少使用或者大部分情况下是只读的字段：
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* wait_table wait_table_hash_nr_entries wait_table_bits
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* 形成等待列队，可以等待某一页可供进程使用 */
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unsigned int inactive_ratio;
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/* 指向这个zone所在的pglist_data对象 */
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struct pglist_data *zone_pgdat;
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/*/这个数组用于实现每个CPU的热/冷页帧列表。内核使用这些列表来保存可用于满足实现的“新鲜”页。但冷热页帧对应的高速缓存状态不同：有些页帧很可能在高速缓存中，因此可以快速访问，故称之为热的；未缓存的页帧与此相对，称之为冷的。*/
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struct per_cpu_pageset __percpu *pageset;
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/*
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* This is a per-zone reserve of pages that are not available
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* to userspace allocations.
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* 每个区域保留的不能被用户空间分配的页面数目
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*/
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unsigned long totalreserve_pages;
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#ifndef CONFIG_SPARSEMEM
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/*
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* Flags for a pageblock_nr_pages block. See pageblock-flags.h.
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* In SPARSEMEM, this map is stored in struct mem_section
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*/
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unsigned long *pageblock_flags;
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#endif /* CONFIG_SPARSEMEM */
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#ifdef CONFIG_NUMA
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/*
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* zone reclaim becomes active if more unmapped pages exist.
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*/
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unsigned long min_unmapped_pages;
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unsigned long min_slab_pages;
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#endif /* CONFIG_NUMA */
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/* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT
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* 只内存域的第一个页帧 */
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unsigned long zone_start_pfn;
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/*
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* spanned_pages is the total pages spanned by the zone, including
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* holes, which is calculated as:
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* spanned_pages = zone_end_pfn - zone_start_pfn;
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*
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* present_pages is physical pages existing within the zone, which
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* is calculated as:
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* present_pages = spanned_pages - absent_pages(pages in holes);
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*
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* managed_pages is present pages managed by the buddy system, which
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* is calculated as (reserved_pages includes pages allocated by the
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* bootmem allocator):
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* managed_pages = present_pages - reserved_pages;
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*
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* So present_pages may be used by memory hotplug or memory power
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* management logic to figure out unmanaged pages by checking
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* (present_pages - managed_pages). And managed_pages should be used
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* by page allocator and vm scanner to calculate all kinds of watermarks
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* and thresholds.
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*
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* Locking rules:
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*
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* zone_start_pfn and spanned_pages are protected by span_seqlock.
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* It is a seqlock because it has to be read outside of zone->lock,
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* and it is done in the main allocator path. But, it is written
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* quite infrequently.
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*
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* The span_seq lock is declared along with zone->lock because it is
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* frequently read in proximity to zone->lock. It's good to
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* give them a chance of being in the same cacheline.
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*
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* Write access to present_pages at runtime should be protected by
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* mem_hotplug_begin/end(). Any reader who can't tolerant drift of
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* present_pages should get_online_mems() to get a stable value.
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*
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* Read access to managed_pages should be safe because it's unsigned
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* long. Write access to zone->managed_pages and totalram_pages are
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* protected by managed_page_count_lock at runtime. Idealy only
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* adjust_managed_page_count() should be used instead of directly
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* touching zone->managed_pages and totalram_pages.
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*/
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unsigned long managed_pages;
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unsigned long spanned_pages; /* 总页数，包含空洞 */
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unsigned long present_pages; /* 可用页数，不包哈空洞 */
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/* 指向管理区的传统名字, "DMA", "NROMAL"或"HIGHMEM" */
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const char *name;
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#ifdef CONFIG_MEMORY_ISOLATION
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/*
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* Number of isolated pageblock. It is used to solve incorrect
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* freepage counting problem due to racy retrieving migratetype
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* of pageblock. Protected by zone->lock.
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*/
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unsigned long nr_isolate_pageblock;
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#endif
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#ifdef CONFIG_MEMORY_HOTPLUG
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/* see spanned/present_pages for more description */
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seqlock_t span_seqlock;
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#endif
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/*
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* wait_table -- the array holding the hash table
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* wait_table_hash_nr_entries -- the size of the hash table array
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* wait_table_bits -- wait_table_size == (1 << wait_table_bits)
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*
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* The purpose of all these is to keep track of the people
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* waiting for a page to become available and make them
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* runnable again when possible. The trouble is that this
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* consumes a lot of space, especially when so few things
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* wait on pages at a given time. So instead of using
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* per-page waitqueues, we use a waitqueue hash table.
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*
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* The bucket discipline is to sleep on the same queue when
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* colliding and wake all in that wait queue when removing.
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* When something wakes, it must check to be sure its page is
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* truly available, a la thundering herd. The cost of a
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* collision is great, but given the expected load of the
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* table, they should be so rare as to be outweighed by the
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* benefits from the saved space.
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*
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* __wait_on_page_locked() and unlock_page() in mm/filemap.c, are the
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* primary users of these fields, and in mm/page_alloc.c
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* free_area_init_core() performs the initialization of them.
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*/
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/* 进程等待队列的散列表, 这些进程正在等待管理区中的某页 */
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wait_queue_head_t *wait_table;
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/* 等待队列散列表中的调度实体数目 */
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unsigned long wait_table_hash_nr_entries;
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/* 等待队列散列表数组大小, 值为2^order */
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unsigned long wait_table_bits;
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ZONE_PADDING(_pad1_)
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/* free areas of different sizes
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页面使用状态的信息，以每个bit标识对应的page是否可以分配
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是用于伙伴系统的，每个数组元素指向对应阶也表的数组开头
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以下是供页帧回收扫描器(page reclaim scanner)访问的字段
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scanner会跟据页帧的活动情况对内存域中使用的页进行编目
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如果页帧被频繁访问，则是活动的，相反则是不活动的，
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在需要换出页帧时，这样的信息是很重要的： */
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struct free_area free_area[MAX_ORDER];
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/* zone flags, see below 描述当前内存的状态, 参见下面的enum zone_flags结构 */
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unsigned long flags;
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/* Write-intensive fields used from the page allocator, 保存该描述符的自旋锁 */
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spinlock_t lock;
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ZONE_PADDING(_pad2_)
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/* Write-intensive fields used by page reclaim */
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/* Fields commonly accessed by the page reclaim scanner */
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spinlock_t lru_lock; /* LRU(最近最少使用算法)活动以及非活动链表使用的自旋锁 */
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struct lruvec lruvec;
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/*
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* When free pages are below this point, additional steps are taken
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* when reading the number of free pages to avoid per-cpu counter
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* drift allowing watermarks to be breached
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* 在空闲页的数目少于这个点percpu_drift_mark的时候
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* 当读取和空闲页数一样的内存页时，系统会采取额外的工作，
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* 防止单CPU页数漂移，从而导致水印被破坏。
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*/
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unsigned long percpu_drift_mark;
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#if defined CONFIG_COMPACTION || defined CONFIG_CMA
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/* pfn where compaction free scanner should start */
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unsigned long compact_cached_free_pfn;
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/* pfn where async and sync compaction migration scanner should start */
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unsigned long compact_cached_migrate_pfn[2];
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#endif
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#ifdef CONFIG_COMPACTION
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/*
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* On compaction failure, 1<<compact_defer_shift compactions
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* are skipped before trying again. The number attempted since
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* last failure is tracked with compact_considered.
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*/
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unsigned int compact_considered;
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unsigned int compact_defer_shift;
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int compact_order_failed;
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#endif
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#if defined CONFIG_COMPACTION || defined CONFIG_CMA
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/* Set to true when the PG_migrate_skip bits should be cleared */
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bool compact_blockskip_flush;
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#endif
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bool contiguous;
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ZONE_PADDING(_pad3_)
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/* Zone statistics 内存域的统计信息, 参见后面的enum zone_stat_item结构 */
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atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
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} ____cacheline_internodealigned_in_smp;
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enum zone_flags
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{
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ZONE_RECLAIM_LOCKED, /* prevents concurrent reclaim */
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ZONE_OOM_LOCKED, /* zone is in OOM killer zonelist */
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ZONE_CONGESTED, /* zone has many dirty pages backed by
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* a congested BDI
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*/
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ZONE_DIRTY, /* reclaim scanning has recently found
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* many dirty file pages at the tail
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* of the LRU.
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*/
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ZONE_WRITEBACK, /* reclaim scanning has recently found
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* many pages under writeback
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*/
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ZONE_FAIR_DEPLETED, /* fair zone policy batch depleted */
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}; |