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![Miaohe Lin](/assets/img/avatar_default.png)
deactivate_swap_slots_cache() and reactivate_swap_slots_cache() are only called below their implementations. So these forward declarations are meaningless and should be removed. Link: https://lkml.kernel.org/r/20210520134022.1370406-4-linmiaohe@huawei.com Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> Cc: Hugh Dickins <hughd@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
351 lines
9.2 KiB
C
351 lines
9.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Manage cache of swap slots to be used for and returned from
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* swap.
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*
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* Copyright(c) 2016 Intel Corporation.
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*
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* Author: Tim Chen <tim.c.chen@linux.intel.com>
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*
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* We allocate the swap slots from the global pool and put
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* it into local per cpu caches. This has the advantage
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* of no needing to acquire the swap_info lock every time
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* we need a new slot.
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*
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* There is also opportunity to simply return the slot
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* to local caches without needing to acquire swap_info
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* lock. We do not reuse the returned slots directly but
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* move them back to the global pool in a batch. This
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* allows the slots to coalesce and reduce fragmentation.
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*
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* The swap entry allocated is marked with SWAP_HAS_CACHE
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* flag in map_count that prevents it from being allocated
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* again from the global pool.
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*
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* The swap slots cache is protected by a mutex instead of
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* a spin lock as when we search for slots with scan_swap_map,
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* we can possibly sleep.
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*/
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#include <linux/swap_slots.h>
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#include <linux/cpu.h>
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#include <linux/cpumask.h>
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#include <linux/vmalloc.h>
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#include <linux/mutex.h>
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#include <linux/mm.h>
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static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
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static bool swap_slot_cache_active;
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bool swap_slot_cache_enabled;
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static bool swap_slot_cache_initialized;
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static DEFINE_MUTEX(swap_slots_cache_mutex);
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/* Serialize swap slots cache enable/disable operations */
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static DEFINE_MUTEX(swap_slots_cache_enable_mutex);
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static void __drain_swap_slots_cache(unsigned int type);
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#define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_enabled)
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#define SLOTS_CACHE 0x1
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#define SLOTS_CACHE_RET 0x2
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static void deactivate_swap_slots_cache(void)
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{
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mutex_lock(&swap_slots_cache_mutex);
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swap_slot_cache_active = false;
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__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
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mutex_unlock(&swap_slots_cache_mutex);
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}
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static void reactivate_swap_slots_cache(void)
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{
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mutex_lock(&swap_slots_cache_mutex);
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swap_slot_cache_active = true;
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mutex_unlock(&swap_slots_cache_mutex);
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}
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/* Must not be called with cpu hot plug lock */
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void disable_swap_slots_cache_lock(void)
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{
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mutex_lock(&swap_slots_cache_enable_mutex);
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swap_slot_cache_enabled = false;
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if (swap_slot_cache_initialized) {
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/* serialize with cpu hotplug operations */
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get_online_cpus();
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__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
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put_online_cpus();
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}
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}
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static void __reenable_swap_slots_cache(void)
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{
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swap_slot_cache_enabled = has_usable_swap();
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}
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void reenable_swap_slots_cache_unlock(void)
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{
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__reenable_swap_slots_cache();
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mutex_unlock(&swap_slots_cache_enable_mutex);
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}
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static bool check_cache_active(void)
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{
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long pages;
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if (!swap_slot_cache_enabled)
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return false;
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pages = get_nr_swap_pages();
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if (!swap_slot_cache_active) {
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if (pages > num_online_cpus() *
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THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE)
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reactivate_swap_slots_cache();
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goto out;
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}
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/* if global pool of slot caches too low, deactivate cache */
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if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE)
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deactivate_swap_slots_cache();
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out:
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return swap_slot_cache_active;
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}
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static int alloc_swap_slot_cache(unsigned int cpu)
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{
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struct swap_slots_cache *cache;
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swp_entry_t *slots, *slots_ret;
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/*
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* Do allocation outside swap_slots_cache_mutex
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* as kvzalloc could trigger reclaim and get_swap_page,
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* which can lock swap_slots_cache_mutex.
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*/
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slots = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
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GFP_KERNEL);
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if (!slots)
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return -ENOMEM;
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slots_ret = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
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GFP_KERNEL);
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if (!slots_ret) {
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kvfree(slots);
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return -ENOMEM;
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}
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mutex_lock(&swap_slots_cache_mutex);
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cache = &per_cpu(swp_slots, cpu);
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if (cache->slots || cache->slots_ret) {
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/* cache already allocated */
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mutex_unlock(&swap_slots_cache_mutex);
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kvfree(slots);
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kvfree(slots_ret);
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return 0;
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}
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if (!cache->lock_initialized) {
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mutex_init(&cache->alloc_lock);
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spin_lock_init(&cache->free_lock);
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cache->lock_initialized = true;
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}
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cache->nr = 0;
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cache->cur = 0;
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cache->n_ret = 0;
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/*
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* We initialized alloc_lock and free_lock earlier. We use
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* !cache->slots or !cache->slots_ret to know if it is safe to acquire
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* the corresponding lock and use the cache. Memory barrier below
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* ensures the assumption.
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*/
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mb();
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cache->slots = slots;
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cache->slots_ret = slots_ret;
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mutex_unlock(&swap_slots_cache_mutex);
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return 0;
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}
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static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
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bool free_slots)
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{
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struct swap_slots_cache *cache;
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swp_entry_t *slots = NULL;
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cache = &per_cpu(swp_slots, cpu);
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if ((type & SLOTS_CACHE) && cache->slots) {
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mutex_lock(&cache->alloc_lock);
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swapcache_free_entries(cache->slots + cache->cur, cache->nr);
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cache->cur = 0;
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cache->nr = 0;
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if (free_slots && cache->slots) {
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kvfree(cache->slots);
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cache->slots = NULL;
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}
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mutex_unlock(&cache->alloc_lock);
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}
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if ((type & SLOTS_CACHE_RET) && cache->slots_ret) {
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spin_lock_irq(&cache->free_lock);
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swapcache_free_entries(cache->slots_ret, cache->n_ret);
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cache->n_ret = 0;
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if (free_slots && cache->slots_ret) {
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slots = cache->slots_ret;
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cache->slots_ret = NULL;
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}
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spin_unlock_irq(&cache->free_lock);
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kvfree(slots);
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}
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}
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static void __drain_swap_slots_cache(unsigned int type)
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{
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unsigned int cpu;
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/*
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* This function is called during
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* 1) swapoff, when we have to make sure no
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* left over slots are in cache when we remove
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* a swap device;
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* 2) disabling of swap slot cache, when we run low
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* on swap slots when allocating memory and need
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* to return swap slots to global pool.
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*
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* We cannot acquire cpu hot plug lock here as
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* this function can be invoked in the cpu
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* hot plug path:
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* cpu_up -> lock cpu_hotplug -> cpu hotplug state callback
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* -> memory allocation -> direct reclaim -> get_swap_page
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* -> drain_swap_slots_cache
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*
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* Hence the loop over current online cpu below could miss cpu that
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* is being brought online but not yet marked as online.
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* That is okay as we do not schedule and run anything on a
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* cpu before it has been marked online. Hence, we will not
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* fill any swap slots in slots cache of such cpu.
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* There are no slots on such cpu that need to be drained.
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*/
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for_each_online_cpu(cpu)
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drain_slots_cache_cpu(cpu, type, false);
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}
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static int free_slot_cache(unsigned int cpu)
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{
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mutex_lock(&swap_slots_cache_mutex);
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drain_slots_cache_cpu(cpu, SLOTS_CACHE | SLOTS_CACHE_RET, true);
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mutex_unlock(&swap_slots_cache_mutex);
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return 0;
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}
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void enable_swap_slots_cache(void)
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{
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mutex_lock(&swap_slots_cache_enable_mutex);
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if (!swap_slot_cache_initialized) {
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int ret;
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ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
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alloc_swap_slot_cache, free_slot_cache);
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if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
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"without swap slots cache.\n", __func__))
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goto out_unlock;
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swap_slot_cache_initialized = true;
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}
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__reenable_swap_slots_cache();
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out_unlock:
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mutex_unlock(&swap_slots_cache_enable_mutex);
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}
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/* called with swap slot cache's alloc lock held */
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static int refill_swap_slots_cache(struct swap_slots_cache *cache)
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{
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if (!use_swap_slot_cache || cache->nr)
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return 0;
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cache->cur = 0;
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if (swap_slot_cache_active)
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cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE,
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cache->slots, 1);
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return cache->nr;
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}
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int free_swap_slot(swp_entry_t entry)
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{
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struct swap_slots_cache *cache;
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cache = raw_cpu_ptr(&swp_slots);
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if (likely(use_swap_slot_cache && cache->slots_ret)) {
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spin_lock_irq(&cache->free_lock);
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/* Swap slots cache may be deactivated before acquiring lock */
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if (!use_swap_slot_cache || !cache->slots_ret) {
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spin_unlock_irq(&cache->free_lock);
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goto direct_free;
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}
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if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) {
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/*
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* Return slots to global pool.
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* The current swap_map value is SWAP_HAS_CACHE.
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* Set it to 0 to indicate it is available for
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* allocation in global pool
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*/
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swapcache_free_entries(cache->slots_ret, cache->n_ret);
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cache->n_ret = 0;
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}
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cache->slots_ret[cache->n_ret++] = entry;
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spin_unlock_irq(&cache->free_lock);
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} else {
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direct_free:
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swapcache_free_entries(&entry, 1);
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}
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return 0;
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}
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swp_entry_t get_swap_page(struct page *page)
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{
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swp_entry_t entry;
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struct swap_slots_cache *cache;
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entry.val = 0;
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if (PageTransHuge(page)) {
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if (IS_ENABLED(CONFIG_THP_SWAP))
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get_swap_pages(1, &entry, HPAGE_PMD_NR);
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goto out;
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}
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/*
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* Preemption is allowed here, because we may sleep
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* in refill_swap_slots_cache(). But it is safe, because
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* accesses to the per-CPU data structure are protected by the
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* mutex cache->alloc_lock.
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*
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* The alloc path here does not touch cache->slots_ret
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* so cache->free_lock is not taken.
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*/
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cache = raw_cpu_ptr(&swp_slots);
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if (likely(check_cache_active() && cache->slots)) {
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mutex_lock(&cache->alloc_lock);
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if (cache->slots) {
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repeat:
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if (cache->nr) {
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entry = cache->slots[cache->cur];
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cache->slots[cache->cur++].val = 0;
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cache->nr--;
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} else if (refill_swap_slots_cache(cache)) {
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goto repeat;
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}
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}
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mutex_unlock(&cache->alloc_lock);
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if (entry.val)
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goto out;
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}
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get_swap_pages(1, &entry, 1);
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out:
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if (mem_cgroup_try_charge_swap(page, entry)) {
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put_swap_page(page, entry);
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entry.val = 0;
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}
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return entry;
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}
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