Add missing diagram from 12.4.1.

lorenzo-stoakes · May 9, 2016 · 4bad9d4 · 4bad9d4
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commit 4bad9d4
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diff --git a/12.md b/12.md
@@ -353,6 +353,56 @@ shmem_swp_alloc
 #define SHMEM_MAX_INDEX  (SHMEM_NR_DIRECT + (ENTRIES_PER_PAGEPAGE/2) * (ENTRIES_PER_PAGE+1))
 ```
 
+* Looking at how indirect blocks are traversed, diagrammatically:
+
+```
+                                                     double-
+                                                 indirect block
+                                                      pages
+                                            /--->--------------- /------>---------------
+                                            |    | swp_entry_t | |       | swp_entry_t |
+                                            |    |-- - -- - -- | |       |-- - -- - -- |
+                                            |    | swp_entry_t | |       | swp_entry_t |
+                                            |    |-- - -- - -- | |       |-- - -- - -- |
+                                            |    | swp_entry_t | |       | swp_entry_t |
+           ---------------------            |    |-- - -- - -- | |       |-- - -- - -- |
+           | inode->i_indirect |            |    | swp_entry_t | |       | swp_entry_t |
+           ---------------------            |    --------------- |       ---------------
+                     |                      |                    |
+                     |                      | /->--------------- | /---->---------------
+                     v indirect block page  | |  | swp_entry_t | | |     | swp_entry_t |
+                     ---------------------- | |  |-- - -- - -- | | |     |-- - -- - -- |
+                   ^ |                   ---/ |  | swp_entry_t | | |     | swp_entry_t |
+ENTRIES_PER_PAGE/2 | |-- - -- - -- - -- - |   |  |-- - -- - -- | | |     |-- - -- - -- |
+                   v |                   -----/  | swp_entry_t | | |     | swp_entry_t |
+                     |--------------------|      |-- - -- - -- | | |     |-- - -- - -- |
+                   ^ |                   -----\  | swp_entry_t | | |     | swp_entry_t |
+ENTRIES_PER_PAGE/2 | |-- - -- - -- - -- - |   |  --------------- | |     ---------------
+                   v |                   ---\ |                  | |
+                     ---------------------- | |      triple-     | |  /->---------------
+                                            | |  indirect block  | |  |  | swp_entry_t |
+                                            | |       pages      | |  |  |-- - -- - -- |
+                                            | \->--------------- | |  |  | swp_entry_t |
+                                            |    |            ---/ |  |  |-- - -- - -- |
+                                            |    |-- - -- - -- |   |  |  | swp_entry_t |
+                                            |    |            -----/  |  |-- - -- - -- |
+                                            |    |-- - -- - -- |      |  | swp_entry_t |
+                                            |    |            --------/  ---------------
+                                            |    |-- - -- - -- |
+                                            |    |            ---------->---------------
+                                            |    ---------------         | swp_entry_t |
+                                            |                            |-- - -- - -- |
+                                            \--->---------------         | swp_entry_t |
+                                                 |            --->       |-- - -- - -- |
+                                                 |-- - -- - -- |         | swp_entry_t |
+                                                 |            --->       |-- - -- - -- |
+                                                 |-- - -- - -- |         | swp_entry_t |
+                                                 |            --->       ---------------
+                                                 |-- - -- - -- |
+                                                 |            --->
+                                                 ---------------
+```
+
 ### 12.4.2 Writing Pages to Swap
 
 * The function [shmem_writepage()][shmem_writepage] is the function registered