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committed 0825a6f9868 * This would not guards us against the user deciding to call swapoff right as/* * Frontswap frontend * * This code provides the generic "frontend" layer to call a matching * "backend" driver implementation of frontswap. See * Documentation/vm/frontswap.rst for more information. * * Copyright (C) 2009-2012 Oracle Corp. All rights reserved. * Author: Dan Magenheimer * * This work is licensed under the terms of the GNU GPL, version 2. */DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);/* * frontswap_ops are added by frontswap_register_ops, and provide the * frontswap "backend" implementation functions. Multiple implementations * may be registered, but implementations can never deregister. This * is a simple singly-linked list of all registered implementations. */static struct frontswap_ops *frontswap_ops __read_mostly;/* * If enabled, frontswap_store will return failure even on success. As * a result, the swap subsystem will always write the page to swap, in * effect converting frontswap into a writethrough cache. In this mode, * there is no direct reduction in swap writes, but a frontswap backend * can unilaterally "reclaim" any pages in use with no data loss, thus * providing increases control over maximum memory usage due to frontswap. */static bool frontswap_writethrough_enabled __read_mostly;/* * If enabled, the underlying tmem implementation is capable of doing * exclusive gets, so frontswap_load, on a successful tmem_get must * mark the page as no longer in frontswap AND mark it dirty. */static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;/* * Counters available via /sys/kernel/debug/frontswap (if debugfs is * properly configured). These are for information only so are not protected * against increment races. */static u64 frontswap_loads;static u64 frontswap_succ_stores;static u64 frontswap_failed_stores;static u64 frontswap_invalidates;