https://github.com/torvalds/linux
Tip revision: 858fd168a95c5b9669aac8db6c14a9aeab446375 authored by Linus Torvalds on 11 June 2023, 21:35:30 UTC
Linux 6.4-rc6
Linux 6.4-rc6
Tip revision: 858fd16
swap_slots.c
// SPDX-License-Identifier: GPL-2.0
/*
* Manage cache of swap slots to be used for and returned from
* swap.
*
* Copyright(c) 2016 Intel Corporation.
*
* Author: Tim Chen <tim.c.chen@linux.intel.com>
*
* We allocate the swap slots from the global pool and put
* it into local per cpu caches. This has the advantage
* of no needing to acquire the swap_info lock every time
* we need a new slot.
*
* There is also opportunity to simply return the slot
* to local caches without needing to acquire swap_info
* lock. We do not reuse the returned slots directly but
* move them back to the global pool in a batch. This
* allows the slots to coalesce and reduce fragmentation.
*
* The swap entry allocated is marked with SWAP_HAS_CACHE
* flag in map_count that prevents it from being allocated
* again from the global pool.
*
* The swap slots cache is protected by a mutex instead of
* a spin lock as when we search for slots with scan_swap_map,
* we can possibly sleep.
*/
#include <linux/swap_slots.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/mutex.h>
#include <linux/mm.h>
static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
static bool swap_slot_cache_active;
bool swap_slot_cache_enabled;
static bool swap_slot_cache_initialized;
static DEFINE_MUTEX(swap_slots_cache_mutex);
/* Serialize swap slots cache enable/disable operations */
static DEFINE_MUTEX(swap_slots_cache_enable_mutex);
static void __drain_swap_slots_cache(unsigned int type);
#define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_enabled)
#define SLOTS_CACHE 0x1
#define SLOTS_CACHE_RET 0x2
static void deactivate_swap_slots_cache(void)
{
mutex_lock(&swap_slots_cache_mutex);
swap_slot_cache_active = false;
__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
mutex_unlock(&swap_slots_cache_mutex);
}
static void reactivate_swap_slots_cache(void)
{
mutex_lock(&swap_slots_cache_mutex);
swap_slot_cache_active = true;
mutex_unlock(&swap_slots_cache_mutex);
}
/* Must not be called with cpu hot plug lock */
void disable_swap_slots_cache_lock(void)
{
mutex_lock(&swap_slots_cache_enable_mutex);
swap_slot_cache_enabled = false;
if (swap_slot_cache_initialized) {
/* serialize with cpu hotplug operations */
cpus_read_lock();
__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
cpus_read_unlock();
}
}
static void __reenable_swap_slots_cache(void)
{
swap_slot_cache_enabled = has_usable_swap();
}
void reenable_swap_slots_cache_unlock(void)
{
__reenable_swap_slots_cache();
mutex_unlock(&swap_slots_cache_enable_mutex);
}
static bool check_cache_active(void)
{
long pages;
if (!swap_slot_cache_enabled)
return false;
pages = get_nr_swap_pages();
if (!swap_slot_cache_active) {
if (pages > num_online_cpus() *
THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE)
reactivate_swap_slots_cache();
goto out;
}
/* if global pool of slot caches too low, deactivate cache */
if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE)
deactivate_swap_slots_cache();
out:
return swap_slot_cache_active;
}
static int alloc_swap_slot_cache(unsigned int cpu)
{
struct swap_slots_cache *cache;
swp_entry_t *slots, *slots_ret;
/*
* Do allocation outside swap_slots_cache_mutex
* as kvzalloc could trigger reclaim and folio_alloc_swap,
* which can lock swap_slots_cache_mutex.
*/
slots = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
GFP_KERNEL);
if (!slots)
return -ENOMEM;
slots_ret = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
GFP_KERNEL);
if (!slots_ret) {
kvfree(slots);
return -ENOMEM;
}
mutex_lock(&swap_slots_cache_mutex);
cache = &per_cpu(swp_slots, cpu);
if (cache->slots || cache->slots_ret) {
/* cache already allocated */
mutex_unlock(&swap_slots_cache_mutex);
kvfree(slots);
kvfree(slots_ret);
return 0;
}
if (!cache->lock_initialized) {
mutex_init(&cache->alloc_lock);
spin_lock_init(&cache->free_lock);
cache->lock_initialized = true;
}
cache->nr = 0;
cache->cur = 0;
cache->n_ret = 0;
/*
* We initialized alloc_lock and free_lock earlier. We use
* !cache->slots or !cache->slots_ret to know if it is safe to acquire
* the corresponding lock and use the cache. Memory barrier below
* ensures the assumption.
*/
mb();
cache->slots = slots;
cache->slots_ret = slots_ret;
mutex_unlock(&swap_slots_cache_mutex);
return 0;
}
static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
bool free_slots)
{
struct swap_slots_cache *cache;
swp_entry_t *slots = NULL;
cache = &per_cpu(swp_slots, cpu);
if ((type & SLOTS_CACHE) && cache->slots) {
mutex_lock(&cache->alloc_lock);
swapcache_free_entries(cache->slots + cache->cur, cache->nr);
cache->cur = 0;
cache->nr = 0;
if (free_slots && cache->slots) {
kvfree(cache->slots);
cache->slots = NULL;
}
mutex_unlock(&cache->alloc_lock);
}
if ((type & SLOTS_CACHE_RET) && cache->slots_ret) {
spin_lock_irq(&cache->free_lock);
swapcache_free_entries(cache->slots_ret, cache->n_ret);
cache->n_ret = 0;
if (free_slots && cache->slots_ret) {
slots = cache->slots_ret;
cache->slots_ret = NULL;
}
spin_unlock_irq(&cache->free_lock);
kvfree(slots);
}
}
static void __drain_swap_slots_cache(unsigned int type)
{
unsigned int cpu;
/*
* This function is called during
* 1) swapoff, when we have to make sure no
* left over slots are in cache when we remove
* a swap device;
* 2) disabling of swap slot cache, when we run low
* on swap slots when allocating memory and need
* to return swap slots to global pool.
*
* We cannot acquire cpu hot plug lock here as
* this function can be invoked in the cpu
* hot plug path:
* cpu_up -> lock cpu_hotplug -> cpu hotplug state callback
* -> memory allocation -> direct reclaim -> folio_alloc_swap
* -> drain_swap_slots_cache
*
* Hence the loop over current online cpu below could miss cpu that
* is being brought online but not yet marked as online.
* That is okay as we do not schedule and run anything on a
* cpu before it has been marked online. Hence, we will not
* fill any swap slots in slots cache of such cpu.
* There are no slots on such cpu that need to be drained.
*/
for_each_online_cpu(cpu)
drain_slots_cache_cpu(cpu, type, false);
}
static int free_slot_cache(unsigned int cpu)
{
mutex_lock(&swap_slots_cache_mutex);
drain_slots_cache_cpu(cpu, SLOTS_CACHE | SLOTS_CACHE_RET, true);
mutex_unlock(&swap_slots_cache_mutex);
return 0;
}
void enable_swap_slots_cache(void)
{
mutex_lock(&swap_slots_cache_enable_mutex);
if (!swap_slot_cache_initialized) {
int ret;
ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
alloc_swap_slot_cache, free_slot_cache);
if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
"without swap slots cache.\n", __func__))
goto out_unlock;
swap_slot_cache_initialized = true;
}
__reenable_swap_slots_cache();
out_unlock:
mutex_unlock(&swap_slots_cache_enable_mutex);
}
/* called with swap slot cache's alloc lock held */
static int refill_swap_slots_cache(struct swap_slots_cache *cache)
{
if (!use_swap_slot_cache)
return 0;
cache->cur = 0;
if (swap_slot_cache_active)
cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE,
cache->slots, 1);
return cache->nr;
}
void free_swap_slot(swp_entry_t entry)
{
struct swap_slots_cache *cache;
cache = raw_cpu_ptr(&swp_slots);
if (likely(use_swap_slot_cache && cache->slots_ret)) {
spin_lock_irq(&cache->free_lock);
/* Swap slots cache may be deactivated before acquiring lock */
if (!use_swap_slot_cache || !cache->slots_ret) {
spin_unlock_irq(&cache->free_lock);
goto direct_free;
}
if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) {
/*
* Return slots to global pool.
* The current swap_map value is SWAP_HAS_CACHE.
* Set it to 0 to indicate it is available for
* allocation in global pool
*/
swapcache_free_entries(cache->slots_ret, cache->n_ret);
cache->n_ret = 0;
}
cache->slots_ret[cache->n_ret++] = entry;
spin_unlock_irq(&cache->free_lock);
} else {
direct_free:
swapcache_free_entries(&entry, 1);
}
}
swp_entry_t folio_alloc_swap(struct folio *folio)
{
swp_entry_t entry;
struct swap_slots_cache *cache;
entry.val = 0;
if (folio_test_large(folio)) {
if (IS_ENABLED(CONFIG_THP_SWAP) && arch_thp_swp_supported())
get_swap_pages(1, &entry, folio_nr_pages(folio));
goto out;
}
/*
* Preemption is allowed here, because we may sleep
* in refill_swap_slots_cache(). But it is safe, because
* accesses to the per-CPU data structure are protected by the
* mutex cache->alloc_lock.
*
* The alloc path here does not touch cache->slots_ret
* so cache->free_lock is not taken.
*/
cache = raw_cpu_ptr(&swp_slots);
if (likely(check_cache_active() && cache->slots)) {
mutex_lock(&cache->alloc_lock);
if (cache->slots) {
repeat:
if (cache->nr) {
entry = cache->slots[cache->cur];
cache->slots[cache->cur++].val = 0;
cache->nr--;
} else if (refill_swap_slots_cache(cache)) {
goto repeat;
}
}
mutex_unlock(&cache->alloc_lock);
if (entry.val)
goto out;
}
get_swap_pages(1, &entry, 1);
out:
if (mem_cgroup_try_charge_swap(folio, entry)) {
put_swap_folio(folio, entry);
entry.val = 0;
}
return entry;
}