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mm/swap: free swap slots in batch
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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.

Link: http://lkml.kernel.org/r/c25e0fcdfd237ec4ca7db91631d3b9f6ed23824e.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Aaron Lu <aaron.lu@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net> escreveu:
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@pdxChen @torvalds
pdxChen authored and torvalds committed Feb 23, 2017
1 parent 36005ba commit 7c00baf
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Showing 2 changed files with 95 additions and 61 deletions.
1 change: 1 addition & 0 deletions include/linux/swap.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -394,6 +394,7 @@ 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);
Expand Down
155 changes: 94 additions & 61 deletions mm/swapfile.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -942,35 +942,34 @@ 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;

Expand All @@ -994,46 +993,52 @@ 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);
}
}

/*
Expand All @@ -1045,8 +1050,10 @@ 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);
}
}

/*
Expand All @@ -1057,8 +1064,32 @@ 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);
}

/*
Expand Down Expand Up @@ -1241,21 +1272,23 @@ 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) {
/*
Expand Down

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