mm: kill frontswap

The only user of frontswap is zswap, and has been for a long time.  Have
swap call into zswap directly and remove the indirection.

[hannes@cmpxchg.org: remove obsolete comment, per Yosry]
  Link: https://lkml.kernel.org/r/20230719142832.GA932528@cmpxchg.org
[fengwei.yin@intel.com: don't warn if none swapcache folio is passed to zswap_load]
  Link: https://lkml.kernel.org/r/20230810095652.3905184-1-fengwei.yin@intel.com
Link: https://lkml.kernel.org/r/20230717160227.GA867137@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 0 insertions, 283 deletions

diff --git a/mm/frontswap.c b/mm/frontswap.c
deleted file mode 100644
index 2fb5df3384b8..000000000000
--- a/mm/frontswap.c
+++ /dev/null
@@ -1,283 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * Frontswap frontend
- *
- * This code provides the generic "frontend" layer to call a matching
- * "backend" driver implementation of frontswap.  See
- * Documentation/mm/frontswap.rst for more information.
- *
- * Copyright (C) 2009-2012 Oracle Corp.  All rights reserved.
- * Author: Dan Magenheimer
- */
-
-#include <linux/mman.h>
-#include <linux/swap.h>
-#include <linux/swapops.h>
-#include <linux/security.h>
-#include <linux/module.h>
-#include <linux/debugfs.h>
-#include <linux/frontswap.h>
-#include <linux/swapfile.h>
-
-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 const struct frontswap_ops *frontswap_ops __read_mostly;
-
-#ifdef CONFIG_DEBUG_FS
-/*
- * 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;
-
-static inline void inc_frontswap_loads(void)
-{
-	data_race(frontswap_loads++);
-}
-static inline void inc_frontswap_succ_stores(void)
-{
-	data_race(frontswap_succ_stores++);
-}
-static inline void inc_frontswap_failed_stores(void)
-{
-	data_race(frontswap_failed_stores++);
-}
-static inline void inc_frontswap_invalidates(void)
-{
-	data_race(frontswap_invalidates++);
-}
-#else
-static inline void inc_frontswap_loads(void) { }
-static inline void inc_frontswap_succ_stores(void) { }
-static inline void inc_frontswap_failed_stores(void) { }
-static inline void inc_frontswap_invalidates(void) { }
-#endif
-
-/*
- * Due to the asynchronous nature of the backends loading potentially
- * _after_ the swap system has been activated, we have chokepoints
- * on all frontswap functions to not call the backend until the backend
- * has registered.
- *
- * This would not guards us against the user deciding to call swapoff right as
- * we are calling the backend to initialize (so swapon is in action).
- * Fortunately for us, the swapon_mutex has been taken by the callee so we are
- * OK. The other scenario where calls to frontswap_store (called via
- * swap_writepage) is racing with frontswap_invalidate_area (called via
- * swapoff) is again guarded by the swap subsystem.
- *
- * While no backend is registered all calls to frontswap_[store|load|
- * invalidate_area|invalidate_page] are ignored or fail.
- *
- * The time between the backend being registered and the swap file system
- * calling the backend (via the frontswap_* functions) is indeterminate as
- * frontswap_ops is not atomic_t (or a value guarded by a spinlock).
- * That is OK as we are comfortable missing some of these calls to the newly
- * registered backend.
- *
- * Obviously the opposite (unloading the backend) must be done after all
- * the frontswap_[store|load|invalidate_area|invalidate_page] start
- * ignoring or failing the requests.  However, there is currently no way
- * to unload a backend once it is registered.
- */
-
-/*
- * Register operations for frontswap
- */
-int frontswap_register_ops(const struct frontswap_ops *ops)
-{
-	if (frontswap_ops)
-		return -EINVAL;
-
-	frontswap_ops = ops;
-	static_branch_inc(&frontswap_enabled_key);
-	return 0;
-}
-
-/*
- * Called when a swap device is swapon'd.
- */
-void frontswap_init(unsigned type, unsigned long *map)
-{
-	struct swap_info_struct *sis = swap_info[type];
-
-	VM_BUG_ON(sis == NULL);
-
-	/*
-	 * p->frontswap is a bitmap that we MUST have to figure out which page
-	 * has gone in frontswap. Without it there is no point of continuing.
-	 */
-	if (WARN_ON(!map))
-		return;
-	/*
-	 * Irregardless of whether the frontswap backend has been loaded
-	 * before this function or it will be later, we _MUST_ have the
-	 * p->frontswap set to something valid to work properly.
-	 */
-	frontswap_map_set(sis, map);
-
-	if (!frontswap_enabled())
-		return;
-	frontswap_ops->init(type);
-}
-
-static bool __frontswap_test(struct swap_info_struct *sis,
-				pgoff_t offset)
-{
-	if (sis->frontswap_map)
-		return test_bit(offset, sis->frontswap_map);
-	return false;
-}
-
-static inline void __frontswap_set(struct swap_info_struct *sis,
-				   pgoff_t offset)
-{
-	set_bit(offset, sis->frontswap_map);
-	atomic_inc(&sis->frontswap_pages);
-}
-
-static inline void __frontswap_clear(struct swap_info_struct *sis,
-				     pgoff_t offset)
-{
-	clear_bit(offset, sis->frontswap_map);
-	atomic_dec(&sis->frontswap_pages);
-}
-
-/*
- * "Store" data from a page to frontswap and associate it with the page's
- * swaptype and offset.  Page must be locked and in the swap cache.
- * If frontswap already contains a page with matching swaptype and
- * offset, the frontswap implementation may either overwrite the data and
- * return success or invalidate the page from frontswap and return failure.
- */
-int __frontswap_store(struct page *page)
-{
-	int ret = -1;
-	swp_entry_t entry = { .val = page_private(page), };
-	int type = swp_type(entry);
-	struct swap_info_struct *sis = swap_info[type];
-	pgoff_t offset = swp_offset(entry);
-
-	VM_BUG_ON(!frontswap_ops);
-	VM_BUG_ON(!PageLocked(page));
-	VM_BUG_ON(sis == NULL);
-
-	/*
-	 * If a dup, we must remove the old page first; we can't leave the
-	 * old page no matter if the store of the new page succeeds or fails,
-	 * and we can't rely on the new page replacing the old page as we may
-	 * not store to the same implementation that contains the old page.
-	 */
-	if (__frontswap_test(sis, offset)) {
-		__frontswap_clear(sis, offset);
-		frontswap_ops->invalidate_page(type, offset);
-	}
-
-	ret = frontswap_ops->store(type, offset, page);
-	if (ret == 0) {
-		__frontswap_set(sis, offset);
-		inc_frontswap_succ_stores();
-	} else {
-		inc_frontswap_failed_stores();
-	}
-
-	return ret;
-}
-
-/*
- * "Get" data from frontswap associated with swaptype and offset that were
- * specified when the data was put to frontswap and use it to fill the
- * specified page with data. Page must be locked and in the swap cache.
- */
-int __frontswap_load(struct page *page)
-{
-	int ret = -1;
-	swp_entry_t entry = { .val = page_private(page), };
-	int type = swp_type(entry);
-	struct swap_info_struct *sis = swap_info[type];
-	pgoff_t offset = swp_offset(entry);
-	bool exclusive = false;
-
-	VM_BUG_ON(!frontswap_ops);
-	VM_BUG_ON(!PageLocked(page));
-	VM_BUG_ON(sis == NULL);
-
-	if (!__frontswap_test(sis, offset))
-		return -1;
-
-	/* Try loading from each implementation, until one succeeds. */
-	ret = frontswap_ops->load(type, offset, page, &exclusive);
-	if (ret == 0) {
-		inc_frontswap_loads();
-		if (exclusive) {
-			SetPageDirty(page);
-			__frontswap_clear(sis, offset);
-		}
-	}
-	return ret;
-}
-
-/*
- * Invalidate any data from frontswap associated with the specified swaptype
- * and offset so that a subsequent "get" will fail.
- */
-void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
-{
-	struct swap_info_struct *sis = swap_info[type];
-
-	VM_BUG_ON(!frontswap_ops);
-	VM_BUG_ON(sis == NULL);
-
-	if (!__frontswap_test(sis, offset))
-		return;
-
-	frontswap_ops->invalidate_page(type, offset);
-	__frontswap_clear(sis, offset);
-	inc_frontswap_invalidates();
-}
-
-/*
- * Invalidate all data from frontswap associated with all offsets for the
- * specified swaptype.
- */
-void __frontswap_invalidate_area(unsigned type)
-{
-	struct swap_info_struct *sis = swap_info[type];
-
-	VM_BUG_ON(!frontswap_ops);
-	VM_BUG_ON(sis == NULL);
-
-	if (sis->frontswap_map == NULL)
-		return;
-
-	frontswap_ops->invalidate_area(type);
-	atomic_set(&sis->frontswap_pages, 0);
-	bitmap_zero(sis->frontswap_map, sis->max);
-}
-
-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", 0444, root, &frontswap_loads);
-	debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_stores);
-	debugfs_create_u64("failed_stores", 0444, root,
-			   &frontswap_failed_stores);
-	debugfs_create_u64("invalidates", 0444, root, &frontswap_invalidates);
-#endif
-	return 0;
-}
-
-module_init(init_frontswap);