Commit ff351f4b authored by Miaohe Lin's avatar Miaohe Lin Committed by Andrew Morton
Browse files

mm/swap: fix comment about swap extent 

Since commit 4efaceb1 ("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.

Link: https://lkml.kernel.org/r/20220509131416.17553-16-linmiaohe@huawei.com


Signed-off-by: default avatarMiaohe Lin <linmiaohe@huawei.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: NeilBrown <neilb@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 133d2743

include/linux/swap.h

+2 −2
Original line number Diff line number Diff line
@@ -168,8 +168,8 @@ 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.

mm/swapfile.c

+6 −9
Original line number Diff line number Diff line
@@ -2208,8 +2208,8 @@ 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.
@@ -2217,12 +2217,12 @@ 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.

 *
@@ -2231,10 +2231,7 @@ 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)

{