Linux Slab分配器(六)--創建slab和銷毀slab

在滿足以下兩個條件時，slab分配器將為高速緩存創建新的slab

1.請求分配對象，但本地高速緩存沒有空閒對象可以分配，需要填充

2.kmem_list3維護的鏈表中沒有slab或者所有的slab都處於FULL鏈表中

這時，調用cache_grow()創建slab增大緩存容量

相關閱讀：

Linux Slab分配器(一)--概述 http://www.linuxidc.com/Linux/2012-06/62965.htm
Linux Slab分配器(二)--初始化 http://www.linuxidc.com/Linux/2012-06/62966.htm
Linux Slab分配器(三)--創建緩存 http://www.linuxidc.com/Linux/2012-06/63109.htm
Linux Slab分配器(四)--分配對象 http://www.linuxidc.com/Linux/2012-06/63138.htm

下圖給出了cache_grow()的代碼流程

1. static int cache_grow(struct kmem_cache *cachep,
2. gfp_t flags, int nodeid, void *objp)
3. {
4. struct slab *slabp;
5. size_t offset;
6. gfp_t local_flags;
7. struct kmem_list3 *l3;
9. /*
10. * Be lazy and only check for valid flags here, keeping it out of the
11. * critical path in kmem_cache_alloc().
12. */
13. BUG_ON(flags & GFP_SLAB_BUG_MASK);
14. local_flags = flags & (GFP_CONSTRAINT_MASK|GFP_RECLAIM_MASK);
16. /* Take the l3 list lock to change the colour_next on this node */
17. check_irq_off();
18. l3 = cachep->nodelists[nodeid];
19. spin_lock(&l3->list_lock);
21. /* Get colour for the slab, and cal the next value. */
22. /*確定待創建的slab的顏色編號*/
23. offset = l3->colour_next;
24. /*更新下一個slab的顏色編號*/
25. l3->colour_next++;
26. /*顏色編號必須小於顏色數*/
27. if (l3->colour_next >= cachep->colour)
28. l3->colour_next = 0;
29. spin_unlock(&l3->list_lock);
31. /*確定待創建的slab的顏色*/
32. offset *= cachep->colour_off;
34. if (local_flags & __GFP_WAIT)
35. local_irq_enable();
37. /*
38. * The test for missing atomic flag is performed here, rather than
39. * the more obvious place, simply to reduce the critical path length
40. * in kmem_cache_alloc(). If a caller is seriously mis-behaving they
41. * will eventually be caught here (where it matters).
42. */
43. kmem_flagcheck(cachep, flags);
45. /*
46. * Get mem for the objs. Attempt to allocate a physical page from
47. * 'nodeid'.
48. */
49. if (!objp)
50. /*從伙伴系統分配頁框，這是slab分配器與伙伴系統的接口*/
51. objp = kmem_getpages(cachep, local_flags, nodeid);
52. if (!objp)
53. goto failed;
55. /* Get slab management. */
56. /*分配slab管理區*/
57. slabp = alloc_slabmgmt(cachep, objp, offset,
58. local_flags & ~GFP_CONSTRAINT_MASK, nodeid);
59. if (!slabp)
60. goto opps1;
62. /*建立頁面到slab和cache的映射，以便於根據obj迅速定位slab描述符和cache描述符*/
63. slab_map_pages(cachep, slabp, objp);
65. /*初始化對象*/
66. cache_init_objs(cachep, slabp);
68. if (local_flags & __GFP_WAIT)
69. local_irq_disable();
70. check_irq_off();
71. spin_lock(&l3->list_lock);
73. /* Make slab active. */
74. /*將新創建的slab添加到free鏈表*/
75. list_add_tail(&slabp->list, &(l3->slabs_free));
76. STATS_INC_GROWN(cachep);
77. l3->free_objects += cachep->num;
78. spin_unlock(&l3->list_lock);
79. return 1;
80. opps1:
81. kmem_freepages(cachep, objp);
82. failed:
83. if (local_flags & __GFP_WAIT)
84. local_irq_disable();
85. return 0;
86. }