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8ea1d2a198
I have noticed that frontswap.h first declares "frontswap_enabled" as extern bool variable, and then overrides it with "#define frontswap_enabled (1)" for CONFIG_FRONTSWAP=Y or (0) when disabled. The bool variable isn't actually instantiated anywhere. This all looks like an unfinished attempt to make frontswap_enabled reflect whether a backend is instantiated. But in the current state, all frontswap hooks call unconditionally into frontswap.c just to check if frontswap_ops is non-NULL. This should at least be checked inline, but we can further eliminate the overhead when CONFIG_FRONTSWAP is enabled and no backend registered, using a static key that is initially disabled, and gets enabled only upon first backend registration. Thus, checks for "frontswap_enabled" are replaced with "frontswap_enabled()" wrapping the static key check. There are two exceptions: - xen's selfballoon_process() was testing frontswap_enabled in code guarded by #ifdef CONFIG_FRONTSWAP, which was effectively always true when reachable. The patch just removes this check. Using frontswap_enabled() does not sound correct here, as this can be true even without xen's own backend being registered. - in SYSCALL_DEFINE2(swapon), change the check to IS_ENABLED(CONFIG_FRONTSWAP) as it seems the bitmap allocation cannot currently be postponed until a backend is registered. This means that frontswap will still have some memory overhead by being configured, but without a backend. After the patch, we can expect that some functions in frontswap.c are called only when frontswap_ops is non-NULL. Change the checks there to VM_BUG_ONs. While at it, convert other BUG_ONs to VM_BUG_ONs as frontswap has been stable for some time. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1463152235-9717-1-git-send-email-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
500 lines
14 KiB
C
500 lines
14 KiB
C
/*
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* Frontswap frontend
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*
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* This code provides the generic "frontend" layer to call a matching
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* "backend" driver implementation of frontswap. See
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* Documentation/vm/frontswap.txt for more information.
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*
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* Copyright (C) 2009-2012 Oracle Corp. All rights reserved.
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* Author: Dan Magenheimer
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*
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* This work is licensed under the terms of the GNU GPL, version 2.
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*/
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#include <linux/mman.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <linux/security.h>
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#include <linux/module.h>
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#include <linux/debugfs.h>
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#include <linux/frontswap.h>
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#include <linux/swapfile.h>
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DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
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/*
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* frontswap_ops are added by frontswap_register_ops, and provide the
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* frontswap "backend" implementation functions. Multiple implementations
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* may be registered, but implementations can never deregister. This
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* is a simple singly-linked list of all registered implementations.
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*/
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static struct frontswap_ops *frontswap_ops __read_mostly;
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#define for_each_frontswap_ops(ops) \
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for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next)
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/*
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* If enabled, frontswap_store will return failure even on success. As
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* a result, the swap subsystem will always write the page to swap, in
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* effect converting frontswap into a writethrough cache. In this mode,
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* there is no direct reduction in swap writes, but a frontswap backend
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* can unilaterally "reclaim" any pages in use with no data loss, thus
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* providing increases control over maximum memory usage due to frontswap.
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*/
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static bool frontswap_writethrough_enabled __read_mostly;
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/*
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* If enabled, the underlying tmem implementation is capable of doing
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* exclusive gets, so frontswap_load, on a successful tmem_get must
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* mark the page as no longer in frontswap AND mark it dirty.
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*/
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static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;
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#ifdef CONFIG_DEBUG_FS
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/*
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* Counters available via /sys/kernel/debug/frontswap (if debugfs is
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* properly configured). These are for information only so are not protected
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* against increment races.
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*/
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static u64 frontswap_loads;
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static u64 frontswap_succ_stores;
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static u64 frontswap_failed_stores;
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static u64 frontswap_invalidates;
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static inline void inc_frontswap_loads(void) {
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frontswap_loads++;
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}
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static inline void inc_frontswap_succ_stores(void) {
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frontswap_succ_stores++;
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}
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static inline void inc_frontswap_failed_stores(void) {
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frontswap_failed_stores++;
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}
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static inline void inc_frontswap_invalidates(void) {
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frontswap_invalidates++;
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}
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#else
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static inline void inc_frontswap_loads(void) { }
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static inline void inc_frontswap_succ_stores(void) { }
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static inline void inc_frontswap_failed_stores(void) { }
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static inline void inc_frontswap_invalidates(void) { }
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#endif
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/*
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* Due to the asynchronous nature of the backends loading potentially
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* _after_ the swap system has been activated, we have chokepoints
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* on all frontswap functions to not call the backend until the backend
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* has registered.
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*
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* This would not guards us against the user deciding to call swapoff right as
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* we are calling the backend to initialize (so swapon is in action).
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* Fortunatly for us, the swapon_mutex has been taked by the callee so we are
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* OK. The other scenario where calls to frontswap_store (called via
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* swap_writepage) is racing with frontswap_invalidate_area (called via
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* swapoff) is again guarded by the swap subsystem.
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*
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* While no backend is registered all calls to frontswap_[store|load|
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* invalidate_area|invalidate_page] are ignored or fail.
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*
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* The time between the backend being registered and the swap file system
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* calling the backend (via the frontswap_* functions) is indeterminate as
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* frontswap_ops is not atomic_t (or a value guarded by a spinlock).
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* That is OK as we are comfortable missing some of these calls to the newly
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* registered backend.
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*
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* Obviously the opposite (unloading the backend) must be done after all
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* the frontswap_[store|load|invalidate_area|invalidate_page] start
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* ignoring or failing the requests. However, there is currently no way
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* to unload a backend once it is registered.
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*/
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/*
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* Register operations for frontswap
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*/
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void frontswap_register_ops(struct frontswap_ops *ops)
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{
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DECLARE_BITMAP(a, MAX_SWAPFILES);
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DECLARE_BITMAP(b, MAX_SWAPFILES);
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struct swap_info_struct *si;
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unsigned int i;
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bitmap_zero(a, MAX_SWAPFILES);
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bitmap_zero(b, MAX_SWAPFILES);
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spin_lock(&swap_lock);
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plist_for_each_entry(si, &swap_active_head, list) {
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if (!WARN_ON(!si->frontswap_map))
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set_bit(si->type, a);
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}
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spin_unlock(&swap_lock);
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/* the new ops needs to know the currently active swap devices */
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for_each_set_bit(i, a, MAX_SWAPFILES)
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ops->init(i);
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/*
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* Setting frontswap_ops must happen after the ops->init() calls
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* above; cmpxchg implies smp_mb() which will ensure the init is
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* complete at this point.
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*/
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do {
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ops->next = frontswap_ops;
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} while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next);
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static_branch_inc(&frontswap_enabled_key);
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spin_lock(&swap_lock);
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plist_for_each_entry(si, &swap_active_head, list) {
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if (si->frontswap_map)
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set_bit(si->type, b);
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}
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spin_unlock(&swap_lock);
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/*
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* On the very unlikely chance that a swap device was added or
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* removed between setting the "a" list bits and the ops init
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* calls, we re-check and do init or invalidate for any changed
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* bits.
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*/
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if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) {
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for (i = 0; i < MAX_SWAPFILES; i++) {
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if (!test_bit(i, a) && test_bit(i, b))
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ops->init(i);
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else if (test_bit(i, a) && !test_bit(i, b))
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ops->invalidate_area(i);
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}
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}
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}
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EXPORT_SYMBOL(frontswap_register_ops);
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/*
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* Enable/disable frontswap writethrough (see above).
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*/
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void frontswap_writethrough(bool enable)
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{
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frontswap_writethrough_enabled = enable;
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}
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EXPORT_SYMBOL(frontswap_writethrough);
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/*
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* Enable/disable frontswap exclusive gets (see above).
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*/
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void frontswap_tmem_exclusive_gets(bool enable)
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{
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frontswap_tmem_exclusive_gets_enabled = enable;
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}
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EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
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/*
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* Called when a swap device is swapon'd.
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*/
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void __frontswap_init(unsigned type, unsigned long *map)
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{
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struct swap_info_struct *sis = swap_info[type];
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struct frontswap_ops *ops;
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VM_BUG_ON(sis == NULL);
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/*
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* p->frontswap is a bitmap that we MUST have to figure out which page
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* has gone in frontswap. Without it there is no point of continuing.
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*/
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if (WARN_ON(!map))
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return;
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/*
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* Irregardless of whether the frontswap backend has been loaded
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* before this function or it will be later, we _MUST_ have the
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* p->frontswap set to something valid to work properly.
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*/
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frontswap_map_set(sis, map);
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for_each_frontswap_ops(ops)
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ops->init(type);
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}
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EXPORT_SYMBOL(__frontswap_init);
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bool __frontswap_test(struct swap_info_struct *sis,
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pgoff_t offset)
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{
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if (sis->frontswap_map)
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return test_bit(offset, sis->frontswap_map);
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return false;
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}
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EXPORT_SYMBOL(__frontswap_test);
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static inline void __frontswap_set(struct swap_info_struct *sis,
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pgoff_t offset)
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{
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set_bit(offset, sis->frontswap_map);
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atomic_inc(&sis->frontswap_pages);
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}
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static inline void __frontswap_clear(struct swap_info_struct *sis,
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pgoff_t offset)
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{
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clear_bit(offset, sis->frontswap_map);
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atomic_dec(&sis->frontswap_pages);
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}
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/*
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* "Store" data from a page to frontswap and associate it with the page's
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* swaptype and offset. Page must be locked and in the swap cache.
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* If frontswap already contains a page with matching swaptype and
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* offset, the frontswap implementation may either overwrite the data and
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* return success or invalidate the page from frontswap and return failure.
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*/
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int __frontswap_store(struct page *page)
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{
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int ret = -1;
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swp_entry_t entry = { .val = page_private(page), };
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int type = swp_type(entry);
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struct swap_info_struct *sis = swap_info[type];
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pgoff_t offset = swp_offset(entry);
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struct frontswap_ops *ops;
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VM_BUG_ON(!frontswap_ops);
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VM_BUG_ON(!PageLocked(page));
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VM_BUG_ON(sis == NULL);
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/*
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* If a dup, we must remove the old page first; we can't leave the
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* old page no matter if the store of the new page succeeds or fails,
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* and we can't rely on the new page replacing the old page as we may
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* not store to the same implementation that contains the old page.
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*/
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if (__frontswap_test(sis, offset)) {
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__frontswap_clear(sis, offset);
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for_each_frontswap_ops(ops)
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ops->invalidate_page(type, offset);
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}
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/* Try to store in each implementation, until one succeeds. */
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for_each_frontswap_ops(ops) {
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ret = ops->store(type, offset, page);
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if (!ret) /* successful store */
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break;
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}
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if (ret == 0) {
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__frontswap_set(sis, offset);
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inc_frontswap_succ_stores();
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} else {
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inc_frontswap_failed_stores();
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}
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if (frontswap_writethrough_enabled)
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/* report failure so swap also writes to swap device */
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ret = -1;
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return ret;
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}
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EXPORT_SYMBOL(__frontswap_store);
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/*
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* "Get" data from frontswap associated with swaptype and offset that were
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* specified when the data was put to frontswap and use it to fill the
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* specified page with data. Page must be locked and in the swap cache.
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*/
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int __frontswap_load(struct page *page)
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{
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int ret = -1;
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swp_entry_t entry = { .val = page_private(page), };
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int type = swp_type(entry);
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struct swap_info_struct *sis = swap_info[type];
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pgoff_t offset = swp_offset(entry);
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struct frontswap_ops *ops;
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VM_BUG_ON(!frontswap_ops);
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VM_BUG_ON(!PageLocked(page));
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VM_BUG_ON(sis == NULL);
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if (!__frontswap_test(sis, offset))
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return -1;
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/* Try loading from each implementation, until one succeeds. */
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for_each_frontswap_ops(ops) {
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ret = ops->load(type, offset, page);
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if (!ret) /* successful load */
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break;
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}
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if (ret == 0) {
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inc_frontswap_loads();
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if (frontswap_tmem_exclusive_gets_enabled) {
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SetPageDirty(page);
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__frontswap_clear(sis, offset);
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}
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}
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return ret;
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}
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EXPORT_SYMBOL(__frontswap_load);
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/*
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* Invalidate any data from frontswap associated with the specified swaptype
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* and offset so that a subsequent "get" will fail.
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*/
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void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
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{
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struct swap_info_struct *sis = swap_info[type];
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struct frontswap_ops *ops;
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VM_BUG_ON(!frontswap_ops);
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VM_BUG_ON(sis == NULL);
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if (!__frontswap_test(sis, offset))
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return;
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for_each_frontswap_ops(ops)
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ops->invalidate_page(type, offset);
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__frontswap_clear(sis, offset);
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inc_frontswap_invalidates();
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}
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EXPORT_SYMBOL(__frontswap_invalidate_page);
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/*
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* Invalidate all data from frontswap associated with all offsets for the
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* specified swaptype.
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*/
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void __frontswap_invalidate_area(unsigned type)
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{
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struct swap_info_struct *sis = swap_info[type];
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struct frontswap_ops *ops;
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VM_BUG_ON(!frontswap_ops);
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VM_BUG_ON(sis == NULL);
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if (sis->frontswap_map == NULL)
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return;
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for_each_frontswap_ops(ops)
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ops->invalidate_area(type);
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atomic_set(&sis->frontswap_pages, 0);
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bitmap_zero(sis->frontswap_map, sis->max);
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}
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EXPORT_SYMBOL(__frontswap_invalidate_area);
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static unsigned long __frontswap_curr_pages(void)
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{
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unsigned long totalpages = 0;
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struct swap_info_struct *si = NULL;
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assert_spin_locked(&swap_lock);
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plist_for_each_entry(si, &swap_active_head, list)
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totalpages += atomic_read(&si->frontswap_pages);
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return totalpages;
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}
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static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
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int *swapid)
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{
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int ret = -EINVAL;
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struct swap_info_struct *si = NULL;
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int si_frontswap_pages;
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unsigned long total_pages_to_unuse = total;
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unsigned long pages = 0, pages_to_unuse = 0;
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assert_spin_locked(&swap_lock);
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plist_for_each_entry(si, &swap_active_head, list) {
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si_frontswap_pages = atomic_read(&si->frontswap_pages);
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if (total_pages_to_unuse < si_frontswap_pages) {
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pages = pages_to_unuse = total_pages_to_unuse;
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} else {
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pages = si_frontswap_pages;
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pages_to_unuse = 0; /* unuse all */
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}
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/* ensure there is enough RAM to fetch pages from frontswap */
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if (security_vm_enough_memory_mm(current->mm, pages)) {
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ret = -ENOMEM;
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continue;
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}
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vm_unacct_memory(pages);
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*unused = pages_to_unuse;
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*swapid = si->type;
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ret = 0;
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break;
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}
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return ret;
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}
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/*
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* Used to check if it's necessory and feasible to unuse pages.
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* Return 1 when nothing to do, 0 when need to shink pages,
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* error code when there is an error.
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*/
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static int __frontswap_shrink(unsigned long target_pages,
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unsigned long *pages_to_unuse,
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int *type)
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{
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unsigned long total_pages = 0, total_pages_to_unuse;
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assert_spin_locked(&swap_lock);
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total_pages = __frontswap_curr_pages();
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if (total_pages <= target_pages) {
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/* Nothing to do */
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*pages_to_unuse = 0;
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return 1;
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}
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total_pages_to_unuse = total_pages - target_pages;
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return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
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}
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/*
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* Frontswap, like a true swap device, may unnecessarily retain pages
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* under certain circumstances; "shrink" frontswap is essentially a
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* "partial swapoff" and works by calling try_to_unuse to attempt to
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* unuse enough frontswap pages to attempt to -- subject to memory
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* constraints -- reduce the number of pages in frontswap to the
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* number given in the parameter target_pages.
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*/
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void frontswap_shrink(unsigned long target_pages)
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{
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unsigned long pages_to_unuse = 0;
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int uninitialized_var(type), ret;
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/*
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* we don't want to hold swap_lock while doing a very
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* lengthy try_to_unuse, but swap_list may change
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* so restart scan from swap_active_head each time
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*/
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spin_lock(&swap_lock);
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ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
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spin_unlock(&swap_lock);
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if (ret == 0)
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try_to_unuse(type, true, pages_to_unuse);
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return;
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}
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EXPORT_SYMBOL(frontswap_shrink);
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/*
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* Count and return the number of frontswap pages across all
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* swap devices. This is exported so that backend drivers can
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* determine current usage without reading debugfs.
|
|
*/
|
|
unsigned long frontswap_curr_pages(void)
|
|
{
|
|
unsigned long totalpages = 0;
|
|
|
|
spin_lock(&swap_lock);
|
|
totalpages = __frontswap_curr_pages();
|
|
spin_unlock(&swap_lock);
|
|
|
|
return totalpages;
|
|
}
|
|
EXPORT_SYMBOL(frontswap_curr_pages);
|
|
|
|
static int __init init_frontswap(void)
|
|
{
|
|
#ifdef CONFIG_DEBUG_FS
|
|
struct dentry *root = debugfs_create_dir("frontswap", NULL);
|
|
if (root == NULL)
|
|
return -ENXIO;
|
|
debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
|
|
debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
|
|
debugfs_create_u64("failed_stores", S_IRUGO, root,
|
|
&frontswap_failed_stores);
|
|
debugfs_create_u64("invalidates", S_IRUGO,
|
|
root, &frontswap_invalidates);
|
|
#endif
|
|
return 0;
|
|
}
|
|
|
|
module_init(init_frontswap);
|