[PATCH 15/15] mm/swap: fix comment about swap extent

[Miaohe Lin <linmiaohe@huawei.com>]

Since commit 4efaceb1c5f8 ("mm, swap: use rbtree for swap_extent"), rbtree
is used for swap extent. Also curr_swap_extent is removed at that time.
Update the corresponding comment.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 include/linux/swap.h |  4 ++--
 mm/swapfile.c        | 15 ++++++---------
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8772132d21dc..e1f3201dec6f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -173,8 +173,8 @@ struct zone;
 
 /*
  * A swap extent maps a range of a swapfile's PAGE_SIZE pages onto a range of
- * disk blocks.  A list of swap extents maps the entire swapfile.  (Where the
- * term `swapfile' refers to either a blockdevice or an IS_REG file.  Apart
+ * disk blocks.  A rbtree of swap extents maps the entire swapfile (Where the
+ * term `swapfile' refers to either a blockdevice or an IS_REG file). Apart
  * from setup, they're handled identically.
  *
  * We always assume that blocks are of size PAGE_SIZE.
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 7ead5fb96d9d..b3f977d9c83e 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2225,8 +2225,8 @@ EXPORT_SYMBOL_GPL(add_swap_extent);
 
 /*
  * A `swap extent' is a simple thing which maps a contiguous range of pages
- * onto a contiguous range of disk blocks.  An ordered list of swap extents
- * is built at swapon time and is then used at swap_writepage/swap_readpage
+ * onto a contiguous range of disk blocks.  A rbtree of swap extents is
+ * built at swapon time and is then used at swap_writepage/swap_readpage
  * time for locating where on disk a page belongs.
  *
  * If the swapfile is an S_ISBLK block device, a single extent is installed.
@@ -2234,12 +2234,12 @@ EXPORT_SYMBOL_GPL(add_swap_extent);
  * swap files identically.
  *
  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
- * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
+ * extent rbtree operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
  * swapfiles are handled *identically* after swapon time.
  *
  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
- * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
- * some stray blocks are found which do not fall within the PAGE_SIZE alignment
+ * and will parse them into a rbtree, in PAGE_SIZE chunks.  If some stray
+ * blocks are found which do not fall within the PAGE_SIZE alignment
  * requirements, they are simply tossed out - we will never use those blocks
  * for swapping.
  *
@@ -2248,10 +2248,7 @@ EXPORT_SYMBOL_GPL(add_swap_extent);
  *
  * The amount of disk space which a single swap extent represents varies.
  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
- * extents in the list.  To avoid much list walking, we cache the previous
- * search location in `curr_swap_extent', and start new searches from there.
- * This is extremely effective.  The average number of iterations in
- * map_swap_page() has been measured at about 0.3 per page.  - akpm.
+ * extents in the rbtree. - akpm.
  */
 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 {
-- 
2.23.0