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![Dan Streetman](/assets/img/avatar_default.png)
Originally get_swap_page() started iterating through the singly-linked list of swap_info_structs using swap_list.next or highest_priority_index, which both were intended to point to the highest priority active swap target that was not full. The first patch in this series changed the singly-linked list to a doubly-linked list, and removed the logic to start at the highest priority non-full entry; it starts scanning at the highest priority entry each time, even if the entry is full. Replace the manually ordered swap_list_head with a plist, swap_active_head. Add a new plist, swap_avail_head. The original swap_active_head plist contains all active swap_info_structs, as before, while the new swap_avail_head plist contains only swap_info_structs that are active and available, i.e. not full. Add a new spinlock, swap_avail_lock, to protect the swap_avail_head list. Mel Gorman suggested using plists since they internally handle ordering the list entries based on priority, which is exactly what swap was doing manually. All the ordering code is now removed, and swap_info_struct entries and simply added to their corresponding plist and automatically ordered correctly. Using a new plist for available swap_info_structs simplifies and optimizes get_swap_page(), which no longer has to iterate over full swap_info_structs. Using a new spinlock for swap_avail_head plist allows each swap_info_struct to add or remove themselves from the plist when they become full or not-full; previously they could not do so because the swap_info_struct->lock is held when they change from full<->not-full, and the swap_lock protecting the main swap_active_head must be ordered before any swap_info_struct->lock. Signed-off-by: Dan Streetman <ddstreet@ieee.org> Acked-by: Mel Gorman <mgorman@suse.de> Cc: Shaohua Li <shli@fusionio.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Hugh Dickins <hughd@google.com> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com> Cc: Weijie Yang <weijieut@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Bob Liu <bob.liu@oracle.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
455 lines
13 KiB
C
455 lines
13 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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/*
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* frontswap_ops is set by frontswap_register_ops to contain the pointers
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* to the frontswap "backend" implementation functions.
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*/
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static struct frontswap_ops *frontswap_ops __read_mostly;
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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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* Specifically when no backend is registered (nobody called
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* frontswap_register_ops) all calls to frontswap_init (which is done via
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* swapon -> enable_swap_info -> frontswap_init) are registered and remembered
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* (via the setting of need_init bitmap) but fail to create tmem_pools. When a
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* backend registers with frontswap at some later point the previous
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* calls to frontswap_init are executed (by iterating over the need_init
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* bitmap) to create tmem_pools and set the respective poolids. All of that is
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* guarded by us using atomic bit operations on the 'need_init' bitmap.
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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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* ignorning or failing the requests - at which point frontswap_ops
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* would have to be made in some fashion atomic.
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*/
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static DECLARE_BITMAP(need_init, MAX_SWAPFILES);
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/*
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* Register operations for frontswap, returning previous thus allowing
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* detection of multiple backends and possible nesting.
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*/
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struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops)
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{
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struct frontswap_ops *old = frontswap_ops;
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int i;
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for (i = 0; i < MAX_SWAPFILES; i++) {
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if (test_and_clear_bit(i, need_init)) {
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struct swap_info_struct *sis = swap_info[i];
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/* __frontswap_init _should_ have set it! */
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if (!sis->frontswap_map)
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return ERR_PTR(-EINVAL);
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ops->init(i);
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}
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}
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/*
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* We MUST have frontswap_ops set _after_ the frontswap_init's
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* have been called. Otherwise __frontswap_store might fail. Hence
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* the barrier to make sure compiler does not re-order us.
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*/
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barrier();
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frontswap_ops = ops;
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return old;
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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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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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if (frontswap_ops)
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frontswap_ops->init(type);
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else {
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BUG_ON(type > MAX_SWAPFILES);
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set_bit(type, need_init);
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}
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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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bool ret = false;
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if (frontswap_ops && sis->frontswap_map)
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ret = test_bit(offset, sis->frontswap_map);
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return ret;
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}
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EXPORT_SYMBOL(__frontswap_test);
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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, dup = 0;
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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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/*
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* Return if no backend registed.
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* Don't need to inc frontswap_failed_stores here.
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*/
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if (!frontswap_ops)
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return ret;
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BUG_ON(!PageLocked(page));
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BUG_ON(sis == NULL);
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if (__frontswap_test(sis, offset))
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dup = 1;
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ret = frontswap_ops->store(type, offset, page);
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if (ret == 0) {
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set_bit(offset, sis->frontswap_map);
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inc_frontswap_succ_stores();
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if (!dup)
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atomic_inc(&sis->frontswap_pages);
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} else {
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/*
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failed dup always results in automatic invalidate of
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the (older) page from frontswap
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*/
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inc_frontswap_failed_stores();
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if (dup)
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__frontswap_clear(sis, offset);
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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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BUG_ON(!PageLocked(page));
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BUG_ON(sis == NULL);
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/*
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* __frontswap_test() will check whether there is backend registered
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*/
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if (__frontswap_test(sis, offset))
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ret = frontswap_ops->load(type, offset, page);
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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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BUG_ON(sis == NULL);
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/*
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* __frontswap_test() will check whether there is backend registered
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*/
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if (__frontswap_test(sis, offset)) {
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frontswap_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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}
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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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if (frontswap_ops) {
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BUG_ON(sis == NULL);
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if (sis->frontswap_map == NULL)
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return;
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frontswap_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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clear_bit(type, need_init);
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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.
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*/
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unsigned long frontswap_curr_pages(void)
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{
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unsigned long totalpages = 0;
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spin_lock(&swap_lock);
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totalpages = __frontswap_curr_pages();
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spin_unlock(&swap_lock);
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return totalpages;
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}
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EXPORT_SYMBOL(frontswap_curr_pages);
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static int __init init_frontswap(void)
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{
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#ifdef CONFIG_DEBUG_FS
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struct dentry *root = debugfs_create_dir("frontswap", NULL);
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if (root == NULL)
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return -ENXIO;
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debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
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debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
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debugfs_create_u64("failed_stores", S_IRUGO, root,
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&frontswap_failed_stores);
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debugfs_create_u64("invalidates", S_IRUGO,
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root, &frontswap_invalidates);
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#endif
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return 0;
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}
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module_init(init_frontswap);
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