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Subject[PATCH 9/9] swap_info: reorder its fields
Reorder (and comment) the fields of swap_info_struct, to make better
use of its cachelines: it's good for swap_duplicate() in particular
if unsigned int max and swap_map are near the start.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
---
include/linux/swap.h | 26 +++++++++++++-------------
1 file changed, 13 insertions(+), 13 deletions(-)
--- si8/include/linux/swap.h 2009-10-14 21:27:07.000000000 +0100
+++ si9/include/linux/swap.h 2009-10-14 21:27:14.000000000 +0100
@@ -167,21 +167,21 @@ struct swap_info_struct {
signed short prio; /* swap priority of this type */
signed char type; /* strange name for an index */
signed char next; /* next type on the swap list */
- struct file *swap_file;
- struct block_device *bdev;
- struct swap_extent first_swap_extent;
- struct swap_extent *curr_swap_extent;
- unsigned char *swap_map;
- unsigned int lowest_bit;
- unsigned int highest_bit;
+ unsigned int max; /* extent of the swap_map */
+ unsigned char *swap_map; /* vmalloc'ed array of usage counts */
+ unsigned int lowest_bit; /* index of first free in swap_map */
+ unsigned int highest_bit; /* index of last free in swap_map */
+ unsigned int pages; /* total of usable pages of swap */
+ unsigned int inuse_pages; /* number of those currently in use */
+ unsigned int cluster_next; /* likely index for next allocation */
+ unsigned int cluster_nr; /* countdown to next cluster search */
unsigned int lowest_alloc; /* while preparing discard cluster */
unsigned int highest_alloc; /* while preparing discard cluster */
- unsigned int cluster_next;
- unsigned int cluster_nr;
- unsigned int pages;
- unsigned int max;
- unsigned int inuse_pages;
- unsigned int old_block_size;
+ struct swap_extent *curr_swap_extent;
+ struct swap_extent first_swap_extent;
+ struct block_device *bdev; /* swap device or bdev of swap file */
+ struct file *swap_file; /* seldom referenced */
+ unsigned int old_block_size; /* seldom referenced */
};

struct swap_list_t {

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