Subject: [PATCH V6 1/4] mm: frontswap: swap data structure changes

From: Dan Magenheimer
Date: Mon Aug 08 2011 - 16:46:56 EST

From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: [PATCH V6 1/4] mm: frontswap: swap data structure changes

This first patch of four in the frontswap series makes available core
swap data structures (swap_lock, swap_list and swap_info) that are
needed by frontswap.c but we don't need to expose them to the dozens
of files that include swap.h so we create a new swapfile.h just to
extern-ify these.

Also add frontswap-related elements to swap_info_struct. Frontswap_map
points to vzalloc'ed one-bit-per-swap-page metadata that indicates
whether the swap page is in frontswap or in the device and frontswap_pages
counts how many pages are in frontswap. We don't tie these to
CONFIG_FRONTSWAP to avoid unnecessary clutter around various frontswap

[v6: rebase to 3.0-rc1]
[v5: no change from v4]
[v4: rebase to 2.6.39]
Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Reviewed-by: Konrad Wilk <konrad.wilk@xxxxxxxxxx>
Acked-by: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx>
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
Cc: Matthew Wilcox <matthew@xxxxxx>
Cc: Chris Mason <chris.mason@xxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxxxx>
Cc: Rik Riel <riel@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

--- linux/include/linux/swapfile.h 1969-12-31 17:00:00.000000000 -0700
+++ frontswap/include/linux/swapfile.h 2011-08-08 08:59:03.951694506 -0600
@@ -0,0 +1,13 @@
+ * these were static in swapfile.c but frontswap.c needs them and we don't
+ * want to expose them to the dozens of source files that include swap.h
+ */
+extern spinlock_t swap_lock;
+extern struct swap_list_t swap_list;
+extern struct swap_info_struct *swap_info[];
+extern int try_to_unuse(unsigned int, bool, unsigned long);
+#endif /* _LINUX_SWAPFILE_H */
--- linux/include/linux/swap.h 2011-08-08 08:19:25.880690134 -0600
+++ frontswap/include/linux/swap.h 2011-08-08 08:59:03.952691415 -0600
@@ -194,6 +194,8 @@ struct swap_info_struct {
struct block_device *bdev; /* swap device or bdev of swap file */
struct file *swap_file; /* seldom referenced */
unsigned int old_block_size; /* seldom referenced */
+ unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
+ unsigned int frontswap_pages; /* frontswap pages in-use counter */

struct swap_list_t {
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