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, 10 insertions, 23 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 346e22b8ae97..e04eb9c0482d 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -35,13 +35,13 @@
 #include <linux/memcontrol.h>
 #include <linux/poll.h>
 #include <linux/oom.h>
-#include <linux/frontswap.h>
 #include <linux/swapfile.h>
 #include <linux/export.h>
 #include <linux/swap_slots.h>
 #include <linux/sort.h>
 #include <linux/completion.h>
 #include <linux/suspend.h>
+#include <linux/zswap.h>
 
 #include <asm/tlbflush.h>
 #include <linux/swapops.h>
@@ -95,7 +95,7 @@ static PLIST_HEAD(swap_active_head);
 static struct plist_head *swap_avail_heads;
 static DEFINE_SPINLOCK(swap_avail_lock);
 
-struct swap_info_struct *swap_info[MAX_SWAPFILES];
+static struct swap_info_struct *swap_info[MAX_SWAPFILES];
 
 static DEFINE_MUTEX(swapon_mutex);
 
@@ -744,7 +744,7 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
 		swap_slot_free_notify = NULL;
 	while (offset <= end) {
 		arch_swap_invalidate_page(si->type, offset);
-		frontswap_invalidate_page(si->type, offset);
+		zswap_invalidate(si->type, offset);
 		if (swap_slot_free_notify)
 			swap_slot_free_notify(si->bdev, offset);
 		offset++;
@@ -2343,11 +2343,10 @@ static void _enable_swap_info(struct swap_info_struct *p)
 
 static void enable_swap_info(struct swap_info_struct *p, int prio,
 				unsigned char *swap_map,
-				struct swap_cluster_info *cluster_info,
-				unsigned long *frontswap_map)
+				struct swap_cluster_info *cluster_info)
 {
-	if (IS_ENABLED(CONFIG_FRONTSWAP))
-		frontswap_init(p->type, frontswap_map);
+	zswap_swapon(p->type);
+
 	spin_lock(&swap_lock);
 	spin_lock(&p->lock);
 	setup_swap_info(p, prio, swap_map, cluster_info);
@@ -2390,7 +2389,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	struct swap_info_struct *p = NULL;
 	unsigned char *swap_map;
 	struct swap_cluster_info *cluster_info;
-	unsigned long *frontswap_map;
 	struct file *swap_file, *victim;
 	struct address_space *mapping;
 	struct inode *inode;
@@ -2515,12 +2513,10 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	p->swap_map = NULL;
 	cluster_info = p->cluster_info;
 	p->cluster_info = NULL;
-	frontswap_map = frontswap_map_get(p);
 	spin_unlock(&p->lock);
 	spin_unlock(&swap_lock);
 	arch_swap_invalidate_area(p->type);
-	frontswap_invalidate_area(p->type);
-	frontswap_map_set(p, NULL);
+	zswap_swapoff(p->type);
 	mutex_unlock(&swapon_mutex);
 	free_percpu(p->percpu_cluster);
 	p->percpu_cluster = NULL;
@@ -2528,7 +2524,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	p->cluster_next_cpu = NULL;
 	vfree(swap_map);
 	kvfree(cluster_info);
-	kvfree(frontswap_map);
 	/* Destroy swap account information */
 	swap_cgroup_swapoff(p->type);
 	exit_swap_address_space(p->type);
@@ -2995,7 +2990,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	unsigned long maxpages;
 	unsigned char *swap_map = NULL;
 	struct swap_cluster_info *cluster_info = NULL;
-	unsigned long *frontswap_map = NULL;
 	struct page *page = NULL;
 	struct inode *inode = NULL;
 	bool inced_nr_rotate_swap = false;
@@ -3135,11 +3129,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		error = nr_extents;
 		goto bad_swap_unlock_inode;
 	}
-	/* frontswap enabled? set up bit-per-page map for frontswap */
-	if (IS_ENABLED(CONFIG_FRONTSWAP))
-		frontswap_map = kvcalloc(BITS_TO_LONGS(maxpages),
-					 sizeof(long),
-					 GFP_KERNEL);
 
 	if ((swap_flags & SWAP_FLAG_DISCARD) &&
 	    p->bdev && bdev_max_discard_sectors(p->bdev)) {
@@ -3192,16 +3181,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (swap_flags & SWAP_FLAG_PREFER)
 		prio =
 		  (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
-	enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);
+	enable_swap_info(p, prio, swap_map, cluster_info);
 
-	pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
+	pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s\n",
 		p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
 		nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
 		(p->flags & SWP_SOLIDSTATE) ? "SS" : "",
 		(p->flags & SWP_DISCARDABLE) ? "D" : "",
 		(p->flags & SWP_AREA_DISCARD) ? "s" : "",
-		(p->flags & SWP_PAGE_DISCARD) ? "c" : "",
-		(frontswap_map) ? "FS" : "");
+		(p->flags & SWP_PAGE_DISCARD) ? "c" : "");
 
 	mutex_unlock(&swapon_mutex);
 	atomic_inc(&proc_poll_event);
@@ -3231,7 +3219,6 @@ bad_swap:
 	spin_unlock(&swap_lock);
 	vfree(swap_map);
 	kvfree(cluster_info);
-	kvfree(frontswap_map);
 	if (inced_nr_rotate_swap)
 		atomic_dec(&nr_rotate_swap);
 	if (swap_file)