Linux 内核 内存管理物理分配页 ④ ( __alloc_pages_nodemask 函数源码分析 | 快速路径 | 慢速路径 | get_page_from_freelist 源码 )

Posted 2022-04-28 韩曙亮

文章目录

• 一、__alloc_pages_nodemask 函数源码分析 ( 快速路径 | 慢速路径 )
• 二、get_page_from_freelist 快速路径 调用函数 完整源码

在 【Linux 内核 内存管理】物理分配页 ② ( __alloc_pages_nodemask 函数参数分析 | __alloc_pages_nodemask 函数分配物理页流程 ) 博客中 , 分析了 __alloc_pages_nodemask 函数分配物理页流程如下 :

首先 , 根据 gfp_t gfp_mask 分配标志位 参数 , 得到 " 内存节点 “ 的 首选 ” 区域类型 " 和 " 迁移类型 " ;

然后 , 执行 " 快速路径 " , 第一次分配 尝试使用 低水线分配 ;

如果上述 " 快速路径 " 分配失败 , 则执行 " 慢速路径 " 分配 ;

上述涉及到了 " 快速路径 " 和 " 慢速路径 " $2$ 种物理页分配方式 ;

一、__alloc_pages_nodemask 函数源码分析 ( 快速路径 | 慢速路径 )

---

在 __alloc_pages_nodemask 函数中 , 先调用 get_page_from_freelist 函数 , 尝试使用 " 快速路径 " 分配内存 , 如果内存分配失败 , 再跳转到 out 处 , 使用 " 慢速路径 " 分配内存 ;

	/* First allocation attempt */
	page = get_page_from_freelist(alloc_mask, order, alloc_flags, &ac);
	if (likely(page))
		goto out;

源码路径 : linux-4.12\\mm\\page_alloc.c#4019

out 标号的代码如下 , 下面是 " 慢速路径 " 分配内存的源码 ;

out:
	if (memcg_kmem_enabled() && (gfp_mask & __GFP_ACCOUNT) && page &&
	    unlikely(memcg_kmem_charge(page, gfp_mask, order) != 0)) 
		__free_pages(page, order);
		page = NULL;
	

	if (kmemcheck_enabled && page)
		kmemcheck_pagealloc_alloc(page, order, gfp_mask);

	trace_mm_page_alloc(page, order, alloc_mask, ac.migratetype);

	return page;

源码路径 : linux-4.12\\mm\\page_alloc.c#4041

__alloc_pages_nodemask 函数完整源码参考 【Linux 内核 内存管理】物理分配页 ① ( 分区伙伴分配器物理分配页核心函数 __alloc_pages_nodemask | __alloc_pages_nodemask 函数完整源码 ) 博客 ;

二、get_page_from_freelist 快速路径 调用函数 完整源码

---

快速路径 调用函数 get_page_from_freelist 函数定义在 Linux 内核源码的 linux-4.12\\mm\\page_alloc.c#3017 位置 ;

/*
 * get_page_from_freelist goes through the zonelist trying to allocate
 * a page.
 */
static struct page *
get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
						const struct alloc_context *ac)

	struct zoneref *z = ac->preferred_zoneref;
	struct zone *zone;
	struct pglist_data *last_pgdat_dirty_limit = NULL;

	/*
	 * Scan zonelist, looking for a zone with enough free.
	 * See also __cpuset_node_allowed() comment in kernel/cpuset.c.
	 */
	for_next_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
								ac->nodemask) 
		struct page *page;
		unsigned long mark;

		if (cpusets_enabled() &&
			(alloc_flags & ALLOC_CPUSET) &&
			!__cpuset_zone_allowed(zone, gfp_mask))
				continue;
		/*
		 * When allocating a page cache page for writing, we
		 * want to get it from a node that is within its dirty
		 * limit, such that no single node holds more than its
		 * proportional share of globally allowed dirty pages.
		 * The dirty limits take into account the node's
		 * lowmem reserves and high watermark so that kswapd
		 * should be able to balance it without having to
		 * write pages from its LRU list.
		 *
		 * XXX: For now, allow allocations to potentially
		 * exceed the per-node dirty limit in the slowpath
		 * (spread_dirty_pages unset) before going into reclaim,
		 * which is important when on a NUMA setup the allowed
		 * nodes are together not big enough to reach the
		 * global limit.  The proper fix for these situations
		 * will require awareness of nodes in the
		 * dirty-throttling and the flusher threads.
		 */
		if (ac->spread_dirty_pages) 
			if (last_pgdat_dirty_limit == zone->zone_pgdat)
				continue;

			if (!node_dirty_ok(zone->zone_pgdat)) 
				last_pgdat_dirty_limit = zone->zone_pgdat;
				continue;
			
		

		mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
		if (!zone_watermark_fast(zone, order, mark,
				       ac_classzone_idx(ac), alloc_flags)) 
			int ret;

			/* Checked here to keep the fast path fast */
			BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);
			if (alloc_flags & ALLOC_NO_WATERMARKS)
				goto try_this_zone;

			if (node_reclaim_mode == 0 ||
			    !zone_allows_reclaim(ac->preferred_zoneref->zone, zone))
				continue;

			ret = node_reclaim(zone->zone_pgdat, gfp_mask, order);
			switch (ret) 
			case NODE_RECLAIM_NOSCAN:
				/* did not scan */
				continue;
			case NODE_RECLAIM_FULL:
				/* scanned but unreclaimable */
				continue;
			default:
				/* did we reclaim enough */
				if (zone_watermark_ok(zone, order, mark,
						ac_classzone_idx(ac), alloc_flags))
					goto try_this_zone;

				continue;
			
		

try_this_zone:
		page = rmqueue(ac->preferred_zoneref->zone, zone, order,
				gfp_mask, alloc_flags, ac->migratetype);
		if (page) 
			prep_new_page(page, order, gfp_mask, alloc_flags);

			/*
			 * If this is a high-order atomic allocation then check
			 * if the pageblock should be reserved for the future
			 */
			if (unlikely(order && (alloc_flags & ALLOC_HARDER)))
				reserve_highatomic_pageblock(page, zone, order);

			return page;
		
	

	return NULL;

源码路径 : linux-4.12\\mm\\page_alloc.c#3017