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Subject[PATCH v4 6/9] mm/swap: Free swap slots in batch
Date
Add new functions that free unused swap slots in batches without
the need to reacquire swap info lock. This improves scalability
and reduce lock contention.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Co-developed-by: "Huang, Ying" <ying.huang@intel.com>
---
include/linux/swap.h | 1 +
mm/swapfile.c | 155 +++++++++++++++++++++++++++++++--------------------
2 files changed, 95 insertions(+), 61 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 68d2ea5..f2bb6ac 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -420,6 +420,7 @@ 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);
+extern void swapcache_free_entries(swp_entry_t *entries, int n);
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 --git a/mm/swapfile.c b/mm/swapfile.c
index 8b2a97e..172fd36 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -949,35 +949,34 @@ static struct swap_info_struct *swap_info_get(swp_entry_t entry)
return p;
}

-static unsigned char swap_entry_free(struct swap_info_struct *p,
- swp_entry_t entry, unsigned char usage,
- bool swap_info_locked)
+static struct swap_info_struct *swap_info_get_cont(swp_entry_t entry,
+ struct swap_info_struct *q)
+{
+ struct swap_info_struct *p;
+
+ p = _swap_info_get(entry);
+
+ if (p != q) {
+ if (q != NULL)
+ spin_unlock(&q->lock);
+ if (p != NULL)
+ spin_lock(&p->lock);
+ }
+ return p;
+}
+
+static unsigned char __swap_entry_free(struct swap_info_struct *p,
+ swp_entry_t entry, unsigned char usage)
{
struct swap_cluster_info *ci;
unsigned long offset = swp_offset(entry);
unsigned char count;
unsigned char has_cache;
- bool lock_swap_info = false;
-
- if (!swap_info_locked) {
- count = p->swap_map[offset];
- if (!p->cluster_info || count == usage || count == SWAP_MAP_SHMEM) {
-lock_swap_info:
- swap_info_locked = true;
- lock_swap_info = true;
- spin_lock(&p->lock);
- }
- }

- ci = lock_cluster(p, offset);
+ ci = lock_cluster_or_swap_info(p, offset);

count = p->swap_map[offset];

- if (!swap_info_locked && (count == usage || count == SWAP_MAP_SHMEM)) {
- unlock_cluster(ci);
- goto lock_swap_info;
- }
-
has_cache = count & SWAP_HAS_CACHE;
count &= ~SWAP_HAS_CACHE;

@@ -1001,46 +1000,52 @@ static unsigned char swap_entry_free(struct swap_info_struct *p,
}

usage = count | has_cache;
- p->swap_map[offset] = usage;
+ p->swap_map[offset] = usage ? : SWAP_HAS_CACHE;
+
+ unlock_cluster_or_swap_info(p, ci);
+
+ return usage;
+}

+static void swap_entry_free(struct swap_info_struct *p, swp_entry_t entry)
+{
+ struct swap_cluster_info *ci;
+ unsigned long offset = swp_offset(entry);
+ unsigned char count;
+
+ ci = lock_cluster(p, offset);
+ count = p->swap_map[offset];
+ VM_BUG_ON(count != SWAP_HAS_CACHE);
+ p->swap_map[offset] = 0;
+ dec_cluster_info_page(p, p->cluster_info, offset);
unlock_cluster(ci);

- /* free if no reference */
- if (!usage) {
- VM_BUG_ON(!swap_info_locked);
- mem_cgroup_uncharge_swap(entry);
- ci = lock_cluster(p, offset);
- dec_cluster_info_page(p, p->cluster_info, offset);
- unlock_cluster(ci);
- if (offset < p->lowest_bit)
- p->lowest_bit = offset;
- 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);
- if (p->flags & SWP_BLKDEV) {
- struct gendisk *disk = p->bdev->bd_disk;
- if (disk->fops->swap_slot_free_notify)
- disk->fops->swap_slot_free_notify(p->bdev,
- offset);
+ mem_cgroup_uncharge_swap(entry);
+ if (offset < p->lowest_bit)
+ p->lowest_bit = offset;
+ 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);
+ if (p->flags & SWP_BLKDEV) {
+ struct gendisk *disk = p->bdev->bd_disk;

- if (lock_swap_info)
- spin_unlock(&p->lock);
-
- return usage;
+ if (disk->fops->swap_slot_free_notify)
+ disk->fops->swap_slot_free_notify(p->bdev,
+ offset);
+ }
}

/*
@@ -1052,8 +1057,10 @@ void swap_free(swp_entry_t entry)
struct swap_info_struct *p;

p = _swap_info_get(entry);
- if (p)
- swap_entry_free(p, entry, 1, false);
+ if (p) {
+ if (!__swap_entry_free(p, entry, 1))
+ swapcache_free_entries(&entry, 1);
+ }
}

/*
@@ -1064,8 +1071,32 @@ void swapcache_free(swp_entry_t entry)
struct swap_info_struct *p;

p = _swap_info_get(entry);
+ if (p) {
+ if (!__swap_entry_free(p, entry, SWAP_HAS_CACHE))
+ swapcache_free_entries(&entry, 1);
+ }
+}
+
+void swapcache_free_entries(swp_entry_t *entries, int n)
+{
+ struct swap_info_struct *p, *prev;
+ int i;
+
+ if (n <= 0)
+ return;
+
+ prev = NULL;
+ p = NULL;
+ for (i = 0; i < n; ++i) {
+ p = swap_info_get_cont(entries[i], prev);
+ if (p)
+ swap_entry_free(p, entries[i]);
+ else
+ break;
+ prev = p;
+ }
if (p)
- swap_entry_free(p, entry, SWAP_HAS_CACHE, false);
+ spin_unlock(&p->lock);
}

/*
@@ -1234,21 +1265,23 @@ int free_swap_and_cache(swp_entry_t entry)
{
struct swap_info_struct *p;
struct page *page = NULL;
+ unsigned char count;

if (non_swap_entry(entry))
return 1;

- p = swap_info_get(entry);
+ p = _swap_info_get(entry);
if (p) {
- if (swap_entry_free(p, entry, 1, true) == SWAP_HAS_CACHE) {
+ count = __swap_entry_free(p, entry, 1);
+ if (count == SWAP_HAS_CACHE) {
page = find_get_page(swap_address_space(entry),
swp_offset(entry));
if (page && !trylock_page(page)) {
put_page(page);
page = NULL;
}
- }
- spin_unlock(&p->lock);
+ } else if (!count)
+ swapcache_free_entries(&entry, 1);
}
if (page) {
/*
--
2.5.5
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