Commit ec8acf20 authored by Shaohua Li's avatar Shaohua Li Committed by Linus Torvalds

swap: add per-partition lock for swapfile

swap_lock is heavily contended when I test swap to 3 fast SSD (even
slightly slower than swap to 2 such SSD).  The main contention comes
from swap_info_get().  This patch tries to fix the gap with adding a new
per-partition lock.

Global data like nr_swapfiles, total_swap_pages, least_priority and
swap_list are still protected by swap_lock.

nr_swap_pages is an atomic now, it can be changed without swap_lock.  In
theory, it's possible get_swap_page() finds no swap pages but actually
there are free swap pages.  But sounds not a big problem.

Accessing partition specific data (like scan_swap_map and so on) is only
protected by swap_info_struct.lock.

Changing swap_info_struct.flags need hold swap_lock and
swap_info_struct.lock, because scan_scan_map() will check it.  read the
flags is ok with either the locks hold.

If both swap_lock and swap_info_struct.lock must be hold, we always hold
the former first to avoid deadlock.

swap_entry_free() can change swap_list.  To delete that code, we add a
new highest_priority_index.  Whenever get_swap_page() is called, we
check it.  If it's valid, we use it.

It's a pity get_swap_page() still holds swap_lock().  But in practice,
swap_lock() isn't heavily contended in my test with this patch (or I can
say there are other much more heavier bottlenecks like TLB flush).  And
BTW, looks get_swap_page() doesn't really need the lock.  We never free
swap_info[] and we check SWAP_WRITEOK flag.  The only risk without the
lock is we could swapout to some low priority swap, but we can quickly
recover after several rounds of swap, so sounds not a big deal to me.
But I'd prefer to fix this if it's a real problem.

"swap: make each swap partition have one address_space" improved the
swapout speed from 1.7G/s to 2G/s.  This patch further improves the
speed to 2.3G/s, so around 15% improvement.  It's a multi-process test,
so TLB flush isn't the biggest bottleneck before the patches.

[arnd@arndb.de: fix it for nommu]
[hughd@google.com: add missing unlock]
[minchan@kernel.org: get rid of lockdep whinge on sys_swapon]
Signed-off-by: default avatarShaohua Li <shli@fusionio.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarMinchan Kim <minchan@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 33806f06
......@@ -57,7 +57,7 @@ void show_mem(unsigned int filter)
printk("Mem-info:\n");
show_free_areas(filter);
printk("Free swap: %6ldkB\n",
nr_swap_pages << (PAGE_SHIFT-10));
get_nr_swap_pages() << (PAGE_SHIFT-10));
printk("%ld pages of RAM\n", totalram_pages);
printk("%ld free pages\n", nr_free_pages());
}
......
......@@ -61,7 +61,7 @@ void show_mem(unsigned int filter)
global_page_state(NR_PAGETABLE),
global_page_state(NR_BOUNCE),
global_page_state(NR_FILE_PAGES),
nr_swap_pages);
get_nr_swap_pages());
for_each_zone(zone) {
unsigned long flags, order, total = 0, largest_order = -1;
......
......@@ -202,6 +202,18 @@ struct swap_info_struct {
unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
atomic_t frontswap_pages; /* frontswap pages in-use counter */
#endif
spinlock_t lock; /*
* protect map scan related fields like
* swap_map, lowest_bit, highest_bit,
* inuse_pages, cluster_next,
* cluster_nr, lowest_alloc and
* highest_alloc. other fields are only
* changed at swapon/swapoff, so are
* protected by swap_lock. changing
* flags need hold this lock and
* swap_lock. If both locks need hold,
* hold swap_lock first.
*/
};
struct swap_list_t {
......@@ -209,9 +221,6 @@ struct swap_list_t {
int next; /* swapfile to be used next */
};
/* Swap 50% full? Release swapcache more aggressively.. */
#define vm_swap_full() (nr_swap_pages*2 < total_swap_pages)
/* linux/mm/page_alloc.c */
extern unsigned long totalram_pages;
extern unsigned long totalreserve_pages;
......@@ -347,8 +356,20 @@ extern struct page *swapin_readahead(swp_entry_t, gfp_t,
struct vm_area_struct *vma, unsigned long addr);
/* linux/mm/swapfile.c */
extern long nr_swap_pages;
extern atomic_long_t nr_swap_pages;
extern long total_swap_pages;
/* Swap 50% full? Release swapcache more aggressively.. */
static inline bool vm_swap_full(void)
{
return atomic_long_read(&nr_swap_pages) * 2 < total_swap_pages;
}
static inline long get_nr_swap_pages(void)
{
return atomic_long_read(&nr_swap_pages);
}
extern void si_swapinfo(struct sysinfo *);
extern swp_entry_t get_swap_page(void);
extern swp_entry_t get_swap_page_of_type(int);
......@@ -381,9 +402,10 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
#else /* CONFIG_SWAP */
#define nr_swap_pages 0L
#define get_nr_swap_pages() 0L
#define total_swap_pages 0L
#define total_swapcache_pages() 0UL
#define vm_swap_full() 0
#define si_swapinfo(val) \
do { (val)->freeswap = (val)->totalswap = 0; } while (0)
......
......@@ -144,7 +144,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
*/
free -= global_page_state(NR_SHMEM);
free += nr_swap_pages;
free += get_nr_swap_pages();
/*
* Any slabs which are created with the
......
......@@ -1907,7 +1907,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
*/
free -= global_page_state(NR_SHMEM);
free += nr_swap_pages;
free += get_nr_swap_pages();
/*
* Any slabs which are created with the
......
......@@ -69,7 +69,8 @@ void show_swap_cache_info(void)
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);
printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10));
printk("Free swap = %ldkB\n",
get_nr_swap_pages() << (PAGE_SHIFT - 10));
printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
}
......
......@@ -47,9 +47,11 @@ static sector_t map_swap_entry(swp_entry_t, struct block_device**);
DEFINE_SPINLOCK(swap_lock);
static unsigned int nr_swapfiles;
long nr_swap_pages;
atomic_long_t nr_swap_pages;
/* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
long total_swap_pages;
static int least_priority;
static atomic_t highest_priority_index = ATOMIC_INIT(-1);
static const char Bad_file[] = "Bad swap file entry ";
static const char Unused_file[] = "Unused swap file entry ";
......@@ -223,7 +225,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
si->lowest_alloc = si->max;
si->highest_alloc = 0;
}
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
/*
* If seek is expensive, start searching for new cluster from
......@@ -242,7 +244,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
if (si->swap_map[offset])
last_in_cluster = offset + SWAPFILE_CLUSTER;
else if (offset == last_in_cluster) {
spin_lock(&swap_lock);
spin_lock(&si->lock);
offset -= SWAPFILE_CLUSTER - 1;
si->cluster_next = offset;
si->cluster_nr = SWAPFILE_CLUSTER - 1;
......@@ -263,7 +265,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
if (si->swap_map[offset])
last_in_cluster = offset + SWAPFILE_CLUSTER;
else if (offset == last_in_cluster) {
spin_lock(&swap_lock);
spin_lock(&si->lock);
offset -= SWAPFILE_CLUSTER - 1;
si->cluster_next = offset;
si->cluster_nr = SWAPFILE_CLUSTER - 1;
......@@ -277,7 +279,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
}
offset = scan_base;
spin_lock(&swap_lock);
spin_lock(&si->lock);
si->cluster_nr = SWAPFILE_CLUSTER - 1;
si->lowest_alloc = 0;
}
......@@ -293,9 +295,9 @@ checks:
/* reuse swap entry of cache-only swap if not busy. */
if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
int swap_was_freed;
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
swap_was_freed = __try_to_reclaim_swap(si, offset);
spin_lock(&swap_lock);
spin_lock(&si->lock);
/* entry was freed successfully, try to use this again */
if (swap_was_freed)
goto checks;
......@@ -335,13 +337,13 @@ checks:
si->lowest_alloc <= last_in_cluster)
last_in_cluster = si->lowest_alloc - 1;
si->flags |= SWP_DISCARDING;
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
if (offset < last_in_cluster)
discard_swap_cluster(si, offset,
last_in_cluster - offset + 1);
spin_lock(&swap_lock);
spin_lock(&si->lock);
si->lowest_alloc = 0;
si->flags &= ~SWP_DISCARDING;
......@@ -355,10 +357,10 @@ checks:
* could defer that delay until swap_writepage,
* but it's easier to keep this self-contained.
*/
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
wait_for_discard, TASK_UNINTERRUPTIBLE);
spin_lock(&swap_lock);
spin_lock(&si->lock);
} else {
/*
* Note pages allocated by racing tasks while
......@@ -374,14 +376,14 @@ checks:
return offset;
scan:
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
while (++offset <= si->highest_bit) {
if (!si->swap_map[offset]) {
spin_lock(&swap_lock);
spin_lock(&si->lock);
goto checks;
}
if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
spin_lock(&swap_lock);
spin_lock(&si->lock);
goto checks;
}
if (unlikely(--latency_ration < 0)) {
......@@ -392,11 +394,11 @@ scan:
offset = si->lowest_bit;
while (++offset < scan_base) {
if (!si->swap_map[offset]) {
spin_lock(&swap_lock);
spin_lock(&si->lock);
goto checks;
}
if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
spin_lock(&swap_lock);
spin_lock(&si->lock);
goto checks;
}
if (unlikely(--latency_ration < 0)) {
......@@ -404,7 +406,7 @@ scan:
latency_ration = LATENCY_LIMIT;
}
}
spin_lock(&swap_lock);
spin_lock(&si->lock);
no_page:
si->flags -= SWP_SCANNING;
......@@ -417,13 +419,34 @@ swp_entry_t get_swap_page(void)
pgoff_t offset;
int type, next;
int wrapped = 0;
int hp_index;
spin_lock(&swap_lock);
if (nr_swap_pages <= 0)
if (atomic_long_read(&nr_swap_pages) <= 0)
goto noswap;
nr_swap_pages--;
atomic_long_dec(&nr_swap_pages);
for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
hp_index = atomic_xchg(&highest_priority_index, -1);
/*
* highest_priority_index records current highest priority swap
* type which just frees swap entries. If its priority is
* higher than that of swap_list.next swap type, we use it. It
* isn't protected by swap_lock, so it can be an invalid value
* if the corresponding swap type is swapoff. We double check
* the flags here. It's even possible the swap type is swapoff
* and swapon again and its priority is changed. In such rare
* case, low prority swap type might be used, but eventually
* high priority swap will be used after several rounds of
* swap.
*/
if (hp_index != -1 && hp_index != type &&
swap_info[type]->prio < swap_info[hp_index]->prio &&
(swap_info[hp_index]->flags & SWP_WRITEOK)) {
type = hp_index;
swap_list.next = type;
}
si = swap_info[type];
next = si->next;
if (next < 0 ||
......@@ -432,22 +455,29 @@ swp_entry_t get_swap_page(void)
wrapped++;
}
if (!si->highest_bit)
spin_lock(&si->lock);
if (!si->highest_bit) {
spin_unlock(&si->lock);
continue;
if (!(si->flags & SWP_WRITEOK))
}
if (!(si->flags & SWP_WRITEOK)) {
spin_unlock(&si->lock);
continue;
}
swap_list.next = next;
spin_unlock(&swap_lock);
/* This is called for allocating swap entry for cache */
offset = scan_swap_map(si, SWAP_HAS_CACHE);
if (offset) {
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
if (offset)
return swp_entry(type, offset);
}
spin_lock(&swap_lock);
next = swap_list.next;
}
nr_swap_pages++;
atomic_long_inc(&nr_swap_pages);
noswap:
spin_unlock(&swap_lock);
return (swp_entry_t) {0};
......@@ -459,19 +489,19 @@ swp_entry_t get_swap_page_of_type(int type)
struct swap_info_struct *si;
pgoff_t offset;
spin_lock(&swap_lock);
si = swap_info[type];
spin_lock(&si->lock);
if (si && (si->flags & SWP_WRITEOK)) {
nr_swap_pages--;
atomic_long_dec(&nr_swap_pages);
/* This is called for allocating swap entry, not cache */
offset = scan_swap_map(si, 1);
if (offset) {
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
return swp_entry(type, offset);
}
nr_swap_pages++;
atomic_long_inc(&nr_swap_pages);
}
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
return (swp_entry_t) {0};
}
......@@ -493,7 +523,7 @@ static struct swap_info_struct *swap_info_get(swp_entry_t entry)
goto bad_offset;
if (!p->swap_map[offset])
goto bad_free;
spin_lock(&swap_lock);
spin_lock(&p->lock);
return p;
bad_free:
......@@ -511,6 +541,27 @@ out:
return NULL;
}
/*
* This swap type frees swap entry, check if it is the highest priority swap
* type which just frees swap entry. get_swap_page() uses
* highest_priority_index to search highest priority swap type. The
* swap_info_struct.lock can't protect us if there are multiple swap types
* active, so we use atomic_cmpxchg.
*/
static void set_highest_priority_index(int type)
{
int old_hp_index, new_hp_index;
do {
old_hp_index = atomic_read(&highest_priority_index);
if (old_hp_index != -1 &&
swap_info[old_hp_index]->prio >= swap_info[type]->prio)
break;
new_hp_index = type;
} while (atomic_cmpxchg(&highest_priority_index,
old_hp_index, new_hp_index) != old_hp_index);
}
static unsigned char swap_entry_free(struct swap_info_struct *p,
swp_entry_t entry, unsigned char usage)
{
......@@ -553,10 +604,8 @@ static unsigned char swap_entry_free(struct swap_info_struct *p,
p->lowest_bit = offset;
if (offset > p->highest_bit)
p->highest_bit = offset;
if (swap_list.next >= 0 &&
p->prio > swap_info[swap_list.next]->prio)
swap_list.next = p->type;
nr_swap_pages++;
set_highest_priority_index(p->type);
atomic_long_inc(&nr_swap_pages);
p->inuse_pages--;
frontswap_invalidate_page(p->type, offset);
if (p->flags & SWP_BLKDEV) {
......@@ -581,7 +630,7 @@ void swap_free(swp_entry_t entry)
p = swap_info_get(entry);
if (p) {
swap_entry_free(p, entry, 1);
spin_unlock(&swap_lock);
spin_unlock(&p->lock);
}
}
......@@ -598,7 +647,7 @@ void swapcache_free(swp_entry_t entry, struct page *page)
count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
if (page)
mem_cgroup_uncharge_swapcache(page, entry, count != 0);
spin_unlock(&swap_lock);
spin_unlock(&p->lock);
}
}
......@@ -617,7 +666,7 @@ int page_swapcount(struct page *page)
p = swap_info_get(entry);
if (p) {
count = swap_count(p->swap_map[swp_offset(entry)]);
spin_unlock(&swap_lock);
spin_unlock(&p->lock);
}
return count;
}
......@@ -706,7 +755,7 @@ int free_swap_and_cache(swp_entry_t entry)
page = NULL;
}
}
spin_unlock(&swap_lock);
spin_unlock(&p->lock);
}
if (page) {
/*
......@@ -804,11 +853,13 @@ unsigned int count_swap_pages(int type, int free)
if ((unsigned int)type < nr_swapfiles) {
struct swap_info_struct *sis = swap_info[type];
spin_lock(&sis->lock);
if (sis->flags & SWP_WRITEOK) {
n = sis->pages;
if (free)
n -= sis->inuse_pages;
}
spin_unlock(&sis->lock);
}
spin_unlock(&swap_lock);
return n;
......@@ -1457,7 +1508,7 @@ static void _enable_swap_info(struct swap_info_struct *p, int prio,
p->swap_map = swap_map;
frontswap_map_set(p, frontswap_map);
p->flags |= SWP_WRITEOK;
nr_swap_pages += p->pages;
atomic_long_add(p->pages, &nr_swap_pages);
total_swap_pages += p->pages;
/* insert swap space into swap_list: */
......@@ -1479,15 +1530,19 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
unsigned long *frontswap_map)
{
spin_lock(&swap_lock);
spin_lock(&p->lock);
_enable_swap_info(p, prio, swap_map, frontswap_map);
frontswap_init(p->type);
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
}
static void reinsert_swap_info(struct swap_info_struct *p)
{
spin_lock(&swap_lock);
spin_lock(&p->lock);
_enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
}
......@@ -1547,14 +1602,16 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
/* just pick something that's safe... */
swap_list.next = swap_list.head;
}
spin_lock(&p->lock);
if (p->prio < 0) {
for (i = p->next; i >= 0; i = swap_info[i]->next)
swap_info[i]->prio = p->prio--;
least_priority++;
}
nr_swap_pages -= p->pages;
atomic_long_sub(p->pages, &nr_swap_pages);
total_swap_pages -= p->pages;
p->flags &= ~SWP_WRITEOK;
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
set_current_oom_origin();
......@@ -1573,14 +1630,17 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
mutex_lock(&swapon_mutex);
spin_lock(&swap_lock);
spin_lock(&p->lock);
drain_mmlist();
/* wait for anyone still in scan_swap_map */
p->highest_bit = 0; /* cuts scans short */
while (p->flags >= SWP_SCANNING) {
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
schedule_timeout_uninterruptible(1);
spin_lock(&swap_lock);
spin_lock(&p->lock);
}
swap_file = p->swap_file;
......@@ -1590,6 +1650,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
p->swap_map = NULL;
p->flags = 0;
frontswap_invalidate_area(type);
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
mutex_unlock(&swapon_mutex);
vfree(swap_map);
......@@ -1795,6 +1856,7 @@ static struct swap_info_struct *alloc_swap_info(void)
p->flags = SWP_USED;
p->next = -1;
spin_unlock(&swap_lock);
spin_lock_init(&p->lock);
return p;
}
......@@ -2117,7 +2179,7 @@ void si_swapinfo(struct sysinfo *val)
if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
nr_to_be_unused += si->inuse_pages;
}
val->freeswap = nr_swap_pages + nr_to_be_unused;
val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
val->totalswap = total_swap_pages + nr_to_be_unused;
spin_unlock(&swap_lock);
}
......@@ -2150,7 +2212,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
p = swap_info[type];
offset = swp_offset(entry);
spin_lock(&swap_lock);
spin_lock(&p->lock);
if (unlikely(offset >= p->max))
goto unlock_out;
......@@ -2185,7 +2247,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
p->swap_map[offset] = count | has_cache;
unlock_out:
spin_unlock(&swap_lock);
spin_unlock(&p->lock);
out:
return err;
......@@ -2310,7 +2372,7 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
}
if (!page) {
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
return -ENOMEM;
}
......@@ -2358,7 +2420,7 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
list_add_tail(&page->lru, &head->lru);
page = NULL; /* now it's attached, don't free it */
out:
spin_unlock(&swap_lock);
spin_unlock(&si->lock);
outer:
if (page)
__free_page(page);
......
......@@ -1684,7 +1684,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
force_scan = true;
/* If we have no swap space, do not bother scanning anon pages. */
if (!sc->may_swap || (nr_swap_pages <= 0)) {
if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
scan_balance = SCAN_FILE;
goto out;
}
......@@ -1933,7 +1933,7 @@ static inline bool should_continue_reclaim(struct zone *zone,
*/
pages_for_compaction = (2UL << sc->order);
inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
if (nr_swap_pages > 0)
if (get_nr_swap_pages() > 0)
inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
if (sc->nr_reclaimed < pages_for_compaction &&
inactive_lru_pages > pages_for_compaction)
......@@ -3085,7 +3085,7 @@ unsigned long global_reclaimable_pages(void)
nr = global_page_state(NR_ACTIVE_FILE) +
global_page_state(NR_INACTIVE_FILE);
if (nr_swap_pages > 0)
if (get_nr_swap_pages() > 0)
nr += global_page_state(NR_ACTIVE_ANON) +
global_page_state(NR_INACTIVE_ANON);
......@@ -3099,7 +3099,7 @@ unsigned long zone_reclaimable_pages(struct zone *zone)
nr = zone_page_state(zone, NR_ACTIVE_FILE) +
zone_page_state(zone, NR_INACTIVE_FILE);
if (nr_swap_pages > 0)
if (get_nr_swap_pages() > 0)
nr += zone_page_state(zone, NR_ACTIVE_ANON) +
zone_page_state(zone, NR_INACTIVE_ANON);
......
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