[v5][PATCH 2/6] mm: swap: make 'struct page' and swp_entry_t variants of swapcache_free().

Dave Hansen
2013-06-03T20:02:10Z

From: Dave Hansen <dave.hansen@linux.intel.com>

swapcache_free() takes two arguments:

void swapcache_free(swp_entry_t entry, struct page *page)

Most of its callers (5/7) are from error handling paths haven't
even instantiated a page, so they pass page=NULL. Both of the
callers that call in with a 'struct page' create and pass in a
temporary swp_entry_t.

Now that we are deferring clearing page_private() until after
swapcache_free() has been called, we can just create a variant
that takes a 'struct page' and does the temporary variable in the
helper.

That leaves all the other callers doing

swapcache_free(entry, NULL)

so create another helper for them that makes it clear that they
need only pass in a swp_entry_t.

One downside here is that delete_from_swap_cache() now calls
swap_address_space() via page_mapping() instead of calling
swap_address_space() directly. In doing so, it removes one more
case of the swap cache code being special-cased, which is a good
thing in my book. But it does cost us a function call.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Minchan Kin <minchan@kernel.org>
---

linux.git-davehans/drivers/staging/zcache/zcache-main.c | 2 +-
linux.git-davehans/include/linux/swap.h | 3 ++-
linux.git-davehans/mm/shmem.c | 2 +-
linux.git-davehans/mm/swap_state.c | 15 +++++----------
linux.git-davehans/mm/swapfile.c | 15 ++++++++++++++-
linux.git-davehans/mm/vmscan.c | 5 +----
6 files changed, 24 insertions(+), 18 deletions(-)

diff -puN drivers/staging/zcache/zcache-main.c~make-page-and-swp_entry_t-variants drivers/staging/zcache/zcache-main.c
--- linux.git/drivers/staging/zcache/zcache-main.c~make-page-and-swp_entry_t-variants 2013-06-03 12:41:30.590715114 -0700
+++ linux.git-davehans/drivers/staging/zcache/zcache-main.c 2013-06-03 12:41:30.602715646 -0700
@@ -961,7 +961,7 @@ static int zcache_get_swap_cache_page(in
* add_to_swap_cache() doesn't return -EEXIST, so we can safely
* clear SWAP_HAS_CACHE flag.
*/
- swapcache_free(entry, NULL);
+ swapcache_free_entry(entry);
/* FIXME: is it possible to get here without err==-ENOMEM?
* If not, we can dispense with the do loop, use goto retry */
} while (err != -ENOMEM);
diff -puN include/linux/swap.h~make-page-and-swp_entry_t-variants include/linux/swap.h
--- linux.git/include/linux/swap.h~make-page-and-swp_entry_t-variants 2013-06-03 12:41:30.591715158 -0700
+++ linux.git-davehans/include/linux/swap.h 2013-06-03 12:41:30.602715646 -0700
@@ -385,7 +385,8 @@ extern void swap_shmem_alloc(swp_entry_t
extern int swap_duplicate(swp_entry_t);
extern int swapcache_prepare(swp_entry_t);
extern void swap_free(swp_entry_t);
-extern void swapcache_free(swp_entry_t, struct page *page);
+extern void swapcache_free_entry(swp_entry_t entry);
+extern void swapcache_free_page_entry(struct page *page);
extern int free_swap_and_cache(swp_entry_t);
extern int swap_type_of(dev_t, sector_t, struct block_device **);
extern unsigned int count_swap_pages(int, int);
diff -puN mm/shmem.c~make-page-and-swp_entry_t-variants mm/shmem.c
--- linux.git/mm/shmem.c~make-page-and-swp_entry_t-variants 2013-06-03 12:41:30.593715247 -0700
+++ linux.git-davehans/mm/shmem.c 2013-06-03 12:41:30.603715690 -0700
@@ -872,7 +872,7 @@ static int shmem_writepage(struct page *
}

mutex_unlock(&shmem_swaplist_mutex);
- swapcache_free(swap, NULL);
+ swapcache_free_entry(swap);
redirty:
set_page_dirty(page);
if (wbc->for_reclaim)
diff -puN mm/swapfile.c~make-page-and-swp_entry_t-variants mm/swapfile.c
--- linux.git/mm/swapfile.c~make-page-and-swp_entry_t-variants 2013-06-03 12:41:30.595715336 -0700
+++ linux.git-davehans/mm/swapfile.c 2013-06-03 12:41:30.604715734 -0700
@@ -637,7 +637,7 @@ void swap_free(swp_entry_t entry)
/*
* Called after dropping swapcache to decrease refcnt to swap entries.
*/
-void swapcache_free(swp_entry_t entry, struct page *page)
+static void __swapcache_free(swp_entry_t entry, struct page *page)
{
struct swap_info_struct *p;
unsigned char count;
@@ -651,6 +651,19 @@ void swapcache_free(swp_entry_t entry, s
}
}

+void swapcache_free_entry(swp_entry_t entry)
+{
+ __swapcache_free(entry, NULL);
+}
+
+void swapcache_free_page_entry(struct page *page)
+{
+ swp_entry_t entry = { .val = page_private(page) };
+ __swapcache_free(entry, page);
+ set_page_private(page, 0);
+ ClearPageSwapCache(page);
+}
+
/*
* How many references to page are currently swapped out?
* This does not give an exact answer when swap count is continued,
diff -puN mm/swap_state.c~make-page-and-swp_entry_t-variants mm/swap_state.c
--- linux.git/mm/swap_state.c~make-page-and-swp_entry_t-variants 2013-06-03 12:41:30.596715380 -0700
+++ linux.git-davehans/mm/swap_state.c 2013-06-03 12:41:30.605715778 -0700
@@ -174,7 +174,7 @@ int add_to_swap(struct page *page, struc

if (unlikely(PageTransHuge(page)))
if (unlikely(split_huge_page_to_list(page, list))) {
- swapcache_free(entry, NULL);
+ swapcache_free_entry(entry);
return 0;
}

@@ -200,7 +200,7 @@ int add_to_swap(struct page *page, struc
* add_to_swap_cache() doesn't return -EEXIST, so we can safely
* clear SWAP_HAS_CACHE flag.
*/
- swapcache_free(entry, NULL);
+ swapcache_free_entry(entry);
return 0;
}
}
@@ -213,19 +213,14 @@ int add_to_swap(struct page *page, struc
*/
void delete_from_swap_cache(struct page *page)
{
- swp_entry_t entry;
struct address_space *address_space;

- entry.val = page_private(page);
-
- address_space = swap_address_space(entry);
+ address_space = page_mapping(page);
spin_lock_irq(&address_space->tree_lock);
__delete_from_swap_cache(page);
spin_unlock_irq(&address_space->tree_lock);

- swapcache_free(entry, page);
- set_page_private(page, 0);
- ClearPageSwapCache(page);
+ swapcache_free_page_entry(page);
page_cache_release(page);
}

@@ -370,7 +365,7 @@ struct page *read_swap_cache_async(swp_e
* add_to_swap_cache() doesn't return -EEXIST, so we can safely
* clear SWAP_HAS_CACHE flag.
*/
- swapcache_free(entry, NULL);
+ swapcache_free_entry(entry);
} while (err != -ENOMEM);

if (new_page)
diff -puN mm/vmscan.c~make-page-and-swp_entry_t-variants mm/vmscan.c
--- linux.git/mm/vmscan.c~make-page-and-swp_entry_t-variants 2013-06-03 12:41:30.598715468 -0700
+++ linux.git-davehans/mm/vmscan.c 2013-06-03 12:41:30.606715822 -0700
@@ -490,12 +490,9 @@ static int __remove_mapping(struct addre
}

if (PageSwapCache(page)) {
- swp_entry_t swap = { .val = page_private(page) };
__delete_from_swap_cache(page);
spin_unlock_irq(&mapping->tree_lock);
- swapcache_free(swap, page);
- set_page_private(page, 0);
- ClearPageSwapCache(page);
+ swapcache_free_page_entry(page);
} else {
void (*freepage)(struct page *);

_