// 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; }