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-rw-r--r--include/linux/swap.h3
-rw-r--r--include/linux/swapfile.h2
-rw-r--r--mm/frontswap.c6
-rw-r--r--mm/swapfile.c145
4 files changed, 97 insertions, 59 deletions
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8bb85d6d65f0..9155bcdcce12 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -214,7 +214,8 @@ struct percpu_cluster {
struct swap_info_struct {
unsigned long flags; /* SWP_USED etc: see above */
signed short prio; /* swap priority of this type */
- struct list_head list; /* entry in swap list */
+ struct plist_node list; /* entry in swap_active_head */
+ struct plist_node avail_list; /* entry in swap_avail_head */
signed char type; /* strange name for an index */
unsigned int max; /* extent of the swap_map */
unsigned char *swap_map; /* vmalloc'ed array of usage counts */
diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
index 2eab382d593d..388293a91e8c 100644
--- a/include/linux/swapfile.h
+++ b/include/linux/swapfile.h
@@ -6,7 +6,7 @@
* want to expose them to the dozens of source files that include swap.h
*/
extern spinlock_t swap_lock;
-extern struct list_head swap_list_head;
+extern struct plist_head swap_active_head;
extern struct swap_info_struct *swap_info[];
extern int try_to_unuse(unsigned int, bool, unsigned long);
diff --git a/mm/frontswap.c b/mm/frontswap.c
index fae11602e8a9..c30eec536f03 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -331,7 +331,7 @@ static unsigned long __frontswap_curr_pages(void)
struct swap_info_struct *si = NULL;
assert_spin_locked(&swap_lock);
- list_for_each_entry(si, &swap_list_head, list)
+ plist_for_each_entry(si, &swap_active_head, list)
totalpages += atomic_read(&si->frontswap_pages);
return totalpages;
}
@@ -346,7 +346,7 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
unsigned long pages = 0, pages_to_unuse = 0;
assert_spin_locked(&swap_lock);
- list_for_each_entry(si, &swap_list_head, list) {
+ plist_for_each_entry(si, &swap_active_head, list) {
si_frontswap_pages = atomic_read(&si->frontswap_pages);
if (total_pages_to_unuse < si_frontswap_pages) {
pages = pages_to_unuse = total_pages_to_unuse;
@@ -408,7 +408,7 @@ void frontswap_shrink(unsigned long target_pages)
/*
* we don't want to hold swap_lock while doing a very
* lengthy try_to_unuse, but swap_list may change
- * so restart scan from swap_list_head each time
+ * so restart scan from swap_active_head each time
*/
spin_lock(&swap_lock);
ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6c95a8c63b1a..beeeef8a1b2d 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -61,7 +61,22 @@ static const char Unused_offset[] = "Unused swap offset entry ";
* all active swap_info_structs
* protected with swap_lock, and ordered by priority.
*/
-LIST_HEAD(swap_list_head);
+PLIST_HEAD(swap_active_head);
+
+/*
+ * all available (active, not full) swap_info_structs
+ * protected with swap_avail_lock, ordered by priority.
+ * This is used by get_swap_page() instead of swap_active_head
+ * because swap_active_head includes all swap_info_structs,
+ * but get_swap_page() doesn't need to look at full ones.
+ * This uses its own lock instead of swap_lock because when a
+ * swap_info_struct changes between not-full/full, it needs to
+ * add/remove itself to/from this list, but the swap_info_struct->lock
+ * is held and the locking order requires swap_lock to be taken
+ * before any swap_info_struct->lock.
+ */
+static PLIST_HEAD(swap_avail_head);
+static DEFINE_SPINLOCK(swap_avail_lock);
struct swap_info_struct *swap_info[MAX_SWAPFILES];
@@ -594,6 +609,9 @@ checks:
if (si->inuse_pages == si->pages) {
si->lowest_bit = si->max;
si->highest_bit = 0;
+ spin_lock(&swap_avail_lock);
+ plist_del(&si->avail_list, &swap_avail_head);
+ spin_unlock(&swap_avail_lock);
}
si->swap_map[offset] = usage;
inc_cluster_info_page(si, si->cluster_info, offset);
@@ -645,57 +663,63 @@ swp_entry_t get_swap_page(void)
{
struct swap_info_struct *si, *next;
pgoff_t offset;
- struct list_head *tmp;
- spin_lock(&swap_lock);
if (atomic_long_read(&nr_swap_pages) <= 0)
goto noswap;
atomic_long_dec(&nr_swap_pages);
- list_for_each(tmp, &swap_list_head) {
- si = list_entry(tmp, typeof(*si), list);
+ spin_lock(&swap_avail_lock);
+
+start_over:
+ plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) {
+ /* requeue si to after same-priority siblings */
+ plist_requeue(&si->avail_list, &swap_avail_head);
+ spin_unlock(&swap_avail_lock);
spin_lock(&si->lock);
if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
+ spin_lock(&swap_avail_lock);
+ if (plist_node_empty(&si->avail_list)) {
+ spin_unlock(&si->lock);
+ goto nextsi;
+ }
+ WARN(!si->highest_bit,
+ "swap_info %d in list but !highest_bit\n",
+ si->type);
+ WARN(!(si->flags & SWP_WRITEOK),
+ "swap_info %d in list but !SWP_WRITEOK\n",
+ si->type);
+ plist_del(&si->avail_list, &swap_avail_head);
spin_unlock(&si->lock);
- continue;
+ goto nextsi;
}
- /*
- * rotate the current swap_info that we're going to use
- * to after any other swap_info that have the same prio,
- * so that all equal-priority swap_info get used equally
- */
- next = si;
- list_for_each_entry_continue(next, &swap_list_head, list) {
- if (si->prio != next->prio)
- break;
- list_rotate_left(&si->list);
- next = si;
- }
-
- spin_unlock(&swap_lock);
/* This is called for allocating swap entry for cache */
offset = scan_swap_map(si, SWAP_HAS_CACHE);
spin_unlock(&si->lock);
if (offset)
return swp_entry(si->type, offset);
- spin_lock(&swap_lock);
+ pr_debug("scan_swap_map of si %d failed to find offset\n",
+ si->type);
+ spin_lock(&swap_avail_lock);
+nextsi:
/*
* if we got here, it's likely that si was almost full before,
* and since scan_swap_map() can drop the si->lock, multiple
* callers probably all tried to get a page from the same si
- * and it filled up before we could get one. So we need to
- * try again. Since we dropped the swap_lock, there may now
- * be non-full higher priority swap_infos, and this si may have
- * even been removed from the list (although very unlikely).
- * Let's start over.
+ * and it filled up before we could get one; or, the si filled
+ * up between us dropping swap_avail_lock and taking si->lock.
+ * Since we dropped the swap_avail_lock, the swap_avail_head
+ * list may have been modified; so if next is still in the
+ * swap_avail_head list then try it, otherwise start over.
*/
- tmp = &swap_list_head;
+ if (plist_node_empty(&next->avail_list))
+ goto start_over;
}
+ spin_unlock(&swap_avail_lock);
+
atomic_long_inc(&nr_swap_pages);
noswap:
- spin_unlock(&swap_lock);
return (swp_entry_t) {0};
}
@@ -798,8 +822,18 @@ static unsigned char swap_entry_free(struct swap_info_struct *p,
dec_cluster_info_page(p, p->cluster_info, offset);
if (offset < p->lowest_bit)
p->lowest_bit = offset;
- if (offset > p->highest_bit)
+ if (offset > p->highest_bit) {
+ bool was_full = !p->highest_bit;
p->highest_bit = offset;
+ if (was_full && (p->flags & SWP_WRITEOK)) {
+ spin_lock(&swap_avail_lock);
+ WARN_ON(!plist_node_empty(&p->avail_list));
+ if (plist_node_empty(&p->avail_list))
+ plist_add(&p->avail_list,
+ &swap_avail_head);
+ spin_unlock(&swap_avail_lock);
+ }
+ }
atomic_long_inc(&nr_swap_pages);
p->inuse_pages--;
frontswap_invalidate_page(p->type, offset);
@@ -1734,12 +1768,16 @@ static void _enable_swap_info(struct swap_info_struct *p, int prio,
unsigned char *swap_map,
struct swap_cluster_info *cluster_info)
{
- struct swap_info_struct *si;
-
if (prio >= 0)
p->prio = prio;
else
p->prio = --least_priority;
+ /*
+ * the plist prio is negated because plist ordering is
+ * low-to-high, while swap ordering is high-to-low
+ */
+ p->list.prio = -p->prio;
+ p->avail_list.prio = -p->prio;
p->swap_map = swap_map;
p->cluster_info = cluster_info;
p->flags |= SWP_WRITEOK;
@@ -1747,27 +1785,20 @@ static void _enable_swap_info(struct swap_info_struct *p, int prio,
total_swap_pages += p->pages;
assert_spin_locked(&swap_lock);
- BUG_ON(!list_empty(&p->list));
- /*
- * insert into swap list; the list is in priority order,
- * so that get_swap_page() can get a page from the highest
- * priority swap_info_struct with available page(s), and
- * swapoff can adjust the auto-assigned (i.e. negative) prio
- * values for any lower-priority swap_info_structs when
- * removing a negative-prio swap_info_struct
- */
- list_for_each_entry(si, &swap_list_head, list) {
- if (p->prio >= si->prio) {
- list_add_tail(&p->list, &si->list);
- return;
- }
- }
/*
- * this covers two cases:
- * 1) p->prio is less than all existing prio
- * 2) the swap list is empty
+ * both lists are plists, and thus priority ordered.
+ * swap_active_head needs to be priority ordered for swapoff(),
+ * which on removal of any swap_info_struct with an auto-assigned
+ * (i.e. negative) priority increments the auto-assigned priority
+ * of any lower-priority swap_info_structs.
+ * swap_avail_head needs to be priority ordered for get_swap_page(),
+ * which allocates swap pages from the highest available priority
+ * swap_info_struct.
*/
- list_add_tail(&p->list, &swap_list_head);
+ plist_add(&p->list, &swap_active_head);
+ spin_lock(&swap_avail_lock);
+ plist_add(&p->avail_list, &swap_avail_head);
+ spin_unlock(&swap_avail_lock);
}
static void enable_swap_info(struct swap_info_struct *p, int prio,
@@ -1821,7 +1852,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
mapping = victim->f_mapping;
spin_lock(&swap_lock);
- list_for_each_entry(p, &swap_list_head, list) {
+ plist_for_each_entry(p, &swap_active_head, list) {
if (p->flags & SWP_WRITEOK) {
if (p->swap_file->f_mapping == mapping) {
found = 1;
@@ -1841,16 +1872,21 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
spin_unlock(&swap_lock);
goto out_dput;
}
+ spin_lock(&swap_avail_lock);
+ plist_del(&p->avail_list, &swap_avail_head);
+ spin_unlock(&swap_avail_lock);
spin_lock(&p->lock);
if (p->prio < 0) {
struct swap_info_struct *si = p;
- list_for_each_entry_continue(si, &swap_list_head, list) {
+ plist_for_each_entry_continue(si, &swap_active_head, list) {
si->prio++;
+ si->list.prio--;
+ si->avail_list.prio--;
}
least_priority++;
}
- list_del_init(&p->list);
+ plist_del(&p->list, &swap_active_head);
atomic_long_sub(p->pages, &nr_swap_pages);
total_swap_pages -= p->pages;
p->flags &= ~SWP_WRITEOK;
@@ -2115,7 +2151,8 @@ static struct swap_info_struct *alloc_swap_info(void)
*/
}
INIT_LIST_HEAD(&p->first_swap_extent.list);
- INIT_LIST_HEAD(&p->list);
+ plist_node_init(&p->list, 0);
+ plist_node_init(&p->avail_list, 0);
p->flags = SWP_USED;
spin_unlock(&swap_lock);
spin_lock_init(&p->lock);
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.