--- /dev/null
+/*
+ * 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 coaellesce 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/vmalloc.h>
+#include <linux/mutex.h>
+
+#ifdef CONFIG_SWAP
+
+static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
+static bool swap_slot_cache_active;
+static bool swap_slot_cache_enabled;
+static bool swap_slot_cache_initialized;
+DEFINE_MUTEX(swap_slots_cache_mutex);
+/* Serialize swap slots cache enable/disable operations */
+DEFINE_MUTEX(swap_slots_cache_enable_mutex);
+
+static void __drain_swap_slots_cache(unsigned int type);
+static void deactivate_swap_slots_cache(void);
+static void reactivate_swap_slots_cache(void);
+
+#define use_swap_slot_cache (swap_slot_cache_active && \
+ swap_slot_cache_enabled && swap_slot_cache_initialized)
+#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 */
+ get_online_cpus();
+ __drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
+ put_online_cpus();
+ }
+}
+
+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 || !swap_slot_cache_initialized)
+ 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 vzalloc could trigger reclaim and get_swap_page,
+ * which can lock swap_slots_cache_mutex.
+ */
+ slots = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE);
+ if (!slots)
+ return -ENOMEM;
+
+ slots_ret = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE);
+ if (!slots_ret) {
+ vfree(slots);
+ return -ENOMEM;
+ }
+
+ mutex_lock(&swap_slots_cache_mutex);
+ cache = &per_cpu(swp_slots, cpu);
+ if (cache->slots || cache->slots_ret)
+ /* cache already allocated */
+ goto out;
+ 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;
+ cache->slots = slots;
+ slots = NULL;
+ cache->slots_ret = slots_ret;
+ slots_ret = NULL;
+out:
+ mutex_unlock(&swap_slots_cache_mutex);
+ if (slots)
+ vfree(slots);
+ if (slots_ret)
+ vfree(slots_ret);
+ 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) {
+ vfree(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);
+ if (slots)
+ vfree(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 -> get_swap_page
+ * -> 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;
+}
+
+int enable_swap_slots_cache(void)
+{
+ int ret = 0;
+
+ mutex_lock(&swap_slots_cache_enable_mutex);
+ if (swap_slot_cache_initialized) {
+ __reenable_swap_slots_cache();
+ goto out_unlock;
+ }
+
+ ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
+ alloc_swap_slot_cache, free_slot_cache);
+ if (ret < 0)
+ goto out_unlock;
+ swap_slot_cache_initialized = true;
+ __reenable_swap_slots_cache();
+out_unlock:
+ mutex_unlock(&swap_slots_cache_enable_mutex);
+ return 0;
+}
+
+/* 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 || cache->nr)
+ return 0;
+
+ cache->cur = 0;
+ if (swap_slot_cache_active)
+ cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE, cache->slots);
+
+ return cache->nr;
+}
+
+int free_swap_slot(swp_entry_t entry)
+{
+ struct swap_slots_cache *cache;
+
+ BUG_ON(!swap_slot_cache_initialized);
+
+ cache = &get_cpu_var(swp_slots);
+ if (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) {
+ 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);
+ }
+ put_cpu_var(swp_slots);
+
+ return 0;
+}
+
+swp_entry_t get_swap_page(void)
+{
+ swp_entry_t entry, *pentry;
+ struct swap_slots_cache *cache;
+
+ /*
+ * 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);
+
+ entry.val = 0;
+ if (check_cache_active()) {
+ mutex_lock(&cache->alloc_lock);
+ if (cache->slots) {
+repeat:
+ if (cache->nr) {
+ pentry = &cache->slots[cache->cur++];
+ entry = *pentry;
+ pentry->val = 0;
+ cache->nr--;
+ } else {
+ if (refill_swap_slots_cache(cache))
+ goto repeat;
+ }
+ }
+ mutex_unlock(&cache->alloc_lock);
+ if (entry.val)
+ return entry;
+ }
+
+ get_swap_pages(1, &entry);
+
+ return entry;
+}
+
+#endif /* CONFIG_SWAP */
projects / mirror_ubuntu-kernels.git / commitdiff