swap: make each swap partition have one address_space
When I use several fast SSD to do swap, swapper_space.tree_lock is
heavily contended. This makes each swap partition have one
address_space to reduce the lock contention. There is an array of
address_space for swap. The swap entry type is the index to the array.
In my test with 3 SSD, this increases the swapout throughput 20%.
[akpm@linux-foundation.org: revert unneeded change to __add_to_swap_cache]
Signed-off-by: Shaohua Li <shli@fusionio.com>
Cc: Hugh Dickins <hughd@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 0cb36fb..8d6644c5 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -36,12 +36,12 @@
.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
};
-struct address_space swapper_space = {
- .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
- .tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
- .a_ops = &swap_aops,
- .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
- .backing_dev_info = &swap_backing_dev_info,
+struct address_space swapper_spaces[MAX_SWAPFILES] = {
+ [0 ... MAX_SWAPFILES - 1] = {
+ .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
+ .a_ops = &swap_aops,
+ .backing_dev_info = &swap_backing_dev_info,
+ }
};
#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
@@ -53,9 +53,19 @@
unsigned long find_total;
} swap_cache_info;
+unsigned long total_swapcache_pages(void)
+{
+ int i;
+ unsigned long ret = 0;
+
+ for (i = 0; i < MAX_SWAPFILES; i++)
+ ret += swapper_spaces[i].nrpages;
+ return ret;
+}
+
void show_swap_cache_info(void)
{
- printk("%lu pages in swap cache\n", total_swapcache_pages);
+ printk("%lu pages in swap cache\n", total_swapcache_pages());
printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
swap_cache_info.add_total, swap_cache_info.del_total,
swap_cache_info.find_success, swap_cache_info.find_total);
@@ -70,6 +80,7 @@
static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
{
int error;
+ struct address_space *address_space;
VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(PageSwapCache(page));
@@ -79,14 +90,16 @@
SetPageSwapCache(page);
set_page_private(page, entry.val);
- spin_lock_irq(&swapper_space.tree_lock);
- error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
+ address_space = swap_address_space(entry);
+ spin_lock_irq(&address_space->tree_lock);
+ error = radix_tree_insert(&address_space->page_tree,
+ entry.val, page);
if (likely(!error)) {
- total_swapcache_pages++;
+ address_space->nrpages++;
__inc_zone_page_state(page, NR_FILE_PAGES);
INC_CACHE_INFO(add_total);
}
- spin_unlock_irq(&swapper_space.tree_lock);
+ spin_unlock_irq(&address_space->tree_lock);
if (unlikely(error)) {
/*
@@ -122,14 +135,19 @@
*/
void __delete_from_swap_cache(struct page *page)
{
+ swp_entry_t entry;
+ struct address_space *address_space;
+
VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(!PageSwapCache(page));
VM_BUG_ON(PageWriteback(page));
- radix_tree_delete(&swapper_space.page_tree, page_private(page));
+ entry.val = page_private(page);
+ address_space = swap_address_space(entry);
+ radix_tree_delete(&address_space->page_tree, page_private(page));
set_page_private(page, 0);
ClearPageSwapCache(page);
- total_swapcache_pages--;
+ address_space->nrpages--;
__dec_zone_page_state(page, NR_FILE_PAGES);
INC_CACHE_INFO(del_total);
}
@@ -195,12 +213,14 @@
void delete_from_swap_cache(struct page *page)
{
swp_entry_t entry;
+ struct address_space *address_space;
entry.val = page_private(page);
- spin_lock_irq(&swapper_space.tree_lock);
+ address_space = swap_address_space(entry);
+ spin_lock_irq(&address_space->tree_lock);
__delete_from_swap_cache(page);
- spin_unlock_irq(&swapper_space.tree_lock);
+ spin_unlock_irq(&address_space->tree_lock);
swapcache_free(entry, page);
page_cache_release(page);
@@ -263,7 +283,7 @@
{
struct page *page;
- page = find_get_page(&swapper_space, entry.val);
+ page = find_get_page(swap_address_space(entry), entry.val);
if (page)
INC_CACHE_INFO(find_success);
@@ -290,7 +310,8 @@
* called after lookup_swap_cache() failed, re-calling
* that would confuse statistics.
*/
- found_page = find_get_page(&swapper_space, entry.val);
+ found_page = find_get_page(swap_address_space(entry),
+ entry.val);
if (found_page)
break;