From: Paolo 'Blaisorblade' Giarrusso <[EMAIL PROTECTED]>
Add some more comments about page->mapping and swapper_space, explaining their
(historical and current) relationship. Such material can be extracted from the
old GIT history (which I used for reference), but having it in the source is
more useful.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <[EMAIL PROTECTED]>
---
linux-2.6.git-paolo/./mm/swap_state.c | 5 +++++
1 files changed, 5 insertions(+)
diff -puN ./mm/swap_state.c~swap-cache-mapping-comment ./mm/swap_state.c
--- linux-2.6.git/./mm/swap_state.c~swap-cache-mapping-comment 2005-08-11
11:12:57.000000000 +0200
+++ linux-2.6.git-paolo/./mm/swap_state.c 2005-08-11 11:12:57.000000000
+0200
@@ -21,6 +21,11 @@
* swapper_space is a fiction, retained to simplify the path through
* vmscan's shrink_list, to make sync_page look nicer, and to allow
* future use of radix_tree tags in the swap cache.
+ *
+ * In 2.4 and until 2.6.6 pages in the swap cache also had page->mapping ==
+ * &swapper_space (this was the definition of PageSwapCache), but this is no
+ * more true. Instead, we use page->flags for that, and page->mapping is
+ * *ignored* here. However, also take a look at page_mapping().
*/
static struct address_space_operations swap_aops = {
.writepage = swap_writepage,
_
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