__alloc_pages

2470 /*
2471  * This is the 'heart' of the zoned buddy allocator.
2472  */
/* 参数理解： */
/* GFP = Get Free Pages ? */
/* 098 typedef struct { DECLARE_BITMAP(bits, MAX_NUMNODES); } nodemask_t; */
/* #define DECLARE_BITMAP(name,bits) 
    unsigned long name[BITS_TO_LONGS(bits)] */
/* typedef struct { unsigned long bits[ BITS_TO_LONGS( MAX_NUMNODES) ]; } nodemask_t */
/* #define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long)) */
/* #define BITS_PER_BYTE 8 */
/* #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d)) */
/* d表示一个数据类型有多少bit， n表示要存储多少位， 现在计算要多少个这样的数据类型 */
/* order 表示 2^order 个页 */
/ zonelist 表示zone的链表 */
2473 struct page *
2474 __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
2475                         struct zonelist *zonelist, nodemask_t *nodemask)
2476 {
2477         enum zone_type high_zoneidx = gfp_zone(gfp_mask);
/* 

0247 static inline enum zone_type gfp_zone(gfp_t flags)
0248 {
0249         enum zone_type z;
0250         int bit = (__force int) (flags & GFP_ZONEMASK); /* 过滤这些标志位吗 ？ */
0251 
0252         z = (GFP_ZONE_TABLE >> (bit * ZONES_SHIFT)) &
0253                                          ((1 << ZONES_SHIFT) - 1);
0254         VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
0255         return z;
0256 }
*/

/*
0219 #define GFP_ZONE_TABLE ( 
0220         (ZONE_NORMAL << 0 * ZONES_SHIFT)                                      
0221         | (OPT_ZONE_DMA << ___GFP_DMA * ZONES_SHIFT)                          
0222         | (OPT_ZONE_HIGHMEM << ___GFP_HIGHMEM * ZONES_SHIFT)                  
0223         | (OPT_ZONE_DMA32 << ___GFP_DMA32 * ZONES_SHIFT)                      
0224         | (ZONE_NORMAL << ___GFP_MOVABLE * ZONES_SHIFT)                       
0225         | (OPT_ZONE_DMA << (___GFP_MOVABLE | ___GFP_DMA) * ZONES_SHIFT)       
0226         | (ZONE_MOVABLE << (___GFP_MOVABLE | ___GFP_HIGHMEM) * ZONES_SHIFT)   
0227         | (OPT_ZONE_DMA32 << (___GFP_MOVABLE | ___GFP_DMA32) * ZONES_SHIFT)   
0228 )
*/
/* #define GFP_ZONEMASK (__GFP_DMA|__GFP_HIGHMEM|__GFP_DMA32|__GFP_MOVABLE) */
/*

0319 #if MAX_NR_ZONES < 2
0320 #define ZONES_SHIFT 0
0321 #elif MAX_NR_ZONES <= 2
0322 #define ZONES_SHIFT 1
0323 #elif MAX_NR_ZONES <= 4
0324 #define ZONES_SHIFT 2
*/
/* 这么多就是要获取zone的下标 */

2478         struct zone *preferred_zone;
2479         struct page *page = NULL;
/* Convert GFP flags to their corresponding migrate type */
2480         int migratetype = allocflags_to_migratetype(gfp_mask);
2481         unsigned int cpuset_mems_cookie;
2482 

0373 /*
0374  * gfp_allowed_mask is set to GFP_BOOT_MASK during early boot to restrict what
0375  * GFP flags are used before interrupts are enabled. Once interrupts are
0376  * enabled, it is set to __GFP_BITS_MASK while the system is running. During
0377  * hibernation, it is used by PM to avoid I/O during memory allocation while
0378  * devices are suspended.
0379  */

2483         gfp_mask &= gfp_allowed_mask;
2484 
2485         lockdep_trace_alloc(gfp_mask);
2486 
/*
0169 #define might_sleep_if(cond) do { if (cond) might_sleep(); } while (0)
*/
2487         might_sleep_if(gfp_mask & __GFP_WAIT);
2488 
2489         if (should_fail_alloc_page(gfp_mask, order))
2490                 return NULL;
2491 
2492         /*
2493          * Check the zones suitable for the gfp_mask contain at least one
2494          * valid zone. It's possible to have an empty zonelist as a result
2495          * of GFP_THISNODE and a memoryless node
2496          */
2497         if (unlikely(!zonelist->_zonerefs->zone))
2498                 return NULL;
2499 
2500 retry_cpuset:
2501         cpuset_mems_cookie = get_mems_allowed();
2502 
2503         /* The preferred zone is used for statistics later */
2504         first_zones_zonelist(zonelist, high_zoneidx,
2505                                 nodemask ? : &cpuset_current_mems_allowed,
2506                                 &preferred_zone);
2507         if (!preferred_zone)
2508                 goto out;
2509 
/*
1779  * get_page_from_freelist goes through the zonelist trying to allocate
1780  * a page.
1781  */ 
1782 static struct page *
1783 get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
1784                 struct zonelist *zonelist, int high_zoneidx, int alloc_flags,
1785                 struct zone *preferred_zone, int migratetype){ ... }
*/

2510         /* First allocation attempt */
2511         page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
2512                         zonelist, high_zoneidx, ALLOC_WMARK_LOW|ALLOC_CPUSET,
2513                         preferred_zone, migratetype);
2514         if (unlikely(!page)) /* 很少失败 */
2515                 page = __alloc_pages_slowpath(gfp_mask, order,
2516                                 zonelist, high_zoneidx, nodemask,
2517                                 preferred_zone, migratetype);
2518 
2519         trace_mm_page_alloc(page, order, gfp_mask, migratetype);
2520 
2521 out:
2522         /*
2523          * When updating a task's mems_allowed, it is possible to race with
2524          * parallel threads in such a way that an allocation can fail while
2525          * the mask is being updated. If a page allocation is about to fail,
2526          * check if the cpuset changed during allocation and if so, retry.
2527          */
2528         if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
2529                 goto retry_cpuset;
2530 
2531         return page;
2532 }