frontswap: remove support for multiple ops

There is only a single instance of frontswap ops in the kernel, so
simplify the frontswap code by removing support for multiple operations.

Link: https://lkml.kernel.org/r/20211224062246.1258487-13-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Konrad Rzeszutek Wilk <Konrad.wilk@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index c5b2848d224049a82036310d01955109525d328d..a631bac12220c5d9847175de1afb69551b33f334 100644 (file)
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -13,10 +13,9 @@ struct frontswap_ops {
        int (*load)(unsigned, pgoff_t, struct page *); /* load a page */
        void (*invalidate_page)(unsigned, pgoff_t); /* page no longer needed */
        void (*invalidate_area)(unsigned); /* swap type just swapoff'ed */
-       struct frontswap_ops *next; /* private pointer to next ops */
 };
 
-extern void frontswap_register_ops(struct frontswap_ops *ops);
+int frontswap_register_ops(const struct frontswap_ops *ops);
 
 extern void frontswap_init(unsigned type, unsigned long *map);
 extern int __frontswap_store(struct page *page);

diff --git a/mm/frontswap.c b/mm/frontswap.c
index 35040fa4eba8389fb37a4455e3b4772e6b1d53a5..6f69b044a8cc749f83592c6adbbb45f0d73545ac 100644 (file)
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -27,10 +27,7 @@ DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
  * 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;
-
-#define for_each_frontswap_ops(ops)            \
-       for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next)
+static const struct frontswap_ops *frontswap_ops __read_mostly;
 
 #ifdef CONFIG_DEBUG_FS
 /*
@@ -97,18 +94,14 @@ static inline void inc_frontswap_invalidates(void) { }
 /*
  * Register operations for frontswap
  */
-void frontswap_register_ops(struct frontswap_ops *ops)
+int frontswap_register_ops(const struct frontswap_ops *ops)
 {
-       /*
-        * Setting frontswap_ops must happen after the ops->init() calls
-        * above; cmpxchg implies smp_mb() which will ensure the init is
-        * complete at this point.
-        */
-       do {
-               ops->next = frontswap_ops;
-       } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next);
+       if (frontswap_ops)
+               return -EINVAL;
 
+       frontswap_ops = ops;
        static_branch_inc(&frontswap_enabled_key);
+       return 0;
 }
 
 /*
@@ -117,7 +110,6 @@ void frontswap_register_ops(struct frontswap_ops *ops)
 void frontswap_init(unsigned type, unsigned long *map)
 {
        struct swap_info_struct *sis = swap_info[type];
-       struct frontswap_ops *ops;
 
        VM_BUG_ON(sis == NULL);
 
@@ -133,9 +125,7 @@ void frontswap_init(unsigned type, unsigned long *map)
         * p->frontswap set to something valid to work properly.
         */
        frontswap_map_set(sis, map);
-
-       for_each_frontswap_ops(ops)
-               ops->init(type);
+       frontswap_ops->init(type);
 }
 
 static bool __frontswap_test(struct swap_info_struct *sis,
@@ -174,7 +164,6 @@ int __frontswap_store(struct page *page)
        int type = swp_type(entry);
        struct swap_info_struct *sis = swap_info[type];
        pgoff_t offset = swp_offset(entry);
-       struct frontswap_ops *ops;
 
        VM_BUG_ON(!frontswap_ops);
        VM_BUG_ON(!PageLocked(page));
@@ -188,16 +177,10 @@ int __frontswap_store(struct page *page)
         */
        if (__frontswap_test(sis, offset)) {
                __frontswap_clear(sis, offset);
-               for_each_frontswap_ops(ops)
-                       ops->invalidate_page(type, offset);
+               frontswap_ops->invalidate_page(type, offset);
        }
 
-       /* Try to store in each implementation, until one succeeds. */
-       for_each_frontswap_ops(ops) {
-               ret = ops->store(type, offset, page);
-               if (!ret) /* successful store */
-                       break;
-       }
+       ret = frontswap_ops->store(type, offset, page);
        if (ret == 0) {
                __frontswap_set(sis, offset);
                inc_frontswap_succ_stores();
@@ -220,7 +203,6 @@ int __frontswap_load(struct page *page)
        int type = swp_type(entry);
        struct swap_info_struct *sis = swap_info[type];
        pgoff_t offset = swp_offset(entry);
-       struct frontswap_ops *ops;
 
        VM_BUG_ON(!frontswap_ops);
        VM_BUG_ON(!PageLocked(page));
@@ -230,11 +212,7 @@ int __frontswap_load(struct page *page)
                return -1;
 
        /* Try loading from each implementation, until one succeeds. */
-       for_each_frontswap_ops(ops) {
-               ret = ops->load(type, offset, page);
-               if (!ret) /* successful load */
-                       break;
-       }
+       ret = frontswap_ops->load(type, offset, page);
        if (ret == 0)
                inc_frontswap_loads();
        return ret;
@@ -247,7 +225,6 @@ int __frontswap_load(struct page *page)
 void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
 {
        struct swap_info_struct *sis = swap_info[type];
-       struct frontswap_ops *ops;
 
        VM_BUG_ON(!frontswap_ops);
        VM_BUG_ON(sis == NULL);
@@ -255,8 +232,7 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
        if (!__frontswap_test(sis, offset))
                return;
 
-       for_each_frontswap_ops(ops)
-               ops->invalidate_page(type, offset);
+       frontswap_ops->invalidate_page(type, offset);
        __frontswap_clear(sis, offset);
        inc_frontswap_invalidates();
 }
@@ -268,7 +244,6 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
 void __frontswap_invalidate_area(unsigned type)
 {
        struct swap_info_struct *sis = swap_info[type];
-       struct frontswap_ops *ops;
 
        VM_BUG_ON(!frontswap_ops);
        VM_BUG_ON(sis == NULL);
@@ -276,8 +251,7 @@ void __frontswap_invalidate_area(unsigned type)
        if (sis->frontswap_map == NULL)
                return;
 
-       for_each_frontswap_ops(ops)
-               ops->invalidate_area(type);
+       frontswap_ops->invalidate_area(type);
        atomic_set(&sis->frontswap_pages, 0);
        bitmap_zero(sis->frontswap_map, sis->max);
 }

diff --git a/mm/zswap.c b/mm/zswap.c
index 7944e3e57e781525738ad1e4ab8ffdf49086eef4..cdf6950fcb2e39718864e38fddab7aa22feaa818 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1378,7 +1378,7 @@ static void zswap_frontswap_init(unsigned type)
        zswap_trees[type] = tree;
 }
 
-static struct frontswap_ops zswap_frontswap_ops = {
+static const struct frontswap_ops zswap_frontswap_ops = {
        .store = zswap_frontswap_store,
        .load = zswap_frontswap_load,
        .invalidate_page = zswap_frontswap_invalidate_page,
@@ -1475,11 +1475,15 @@ static int __init init_zswap(void)
        if (!shrink_wq)
                goto fallback_fail;
 
-       frontswap_register_ops(&zswap_frontswap_ops);
+       ret = frontswap_register_ops(&zswap_frontswap_ops);
+       if (ret)
+               goto destroy_wq;
        if (zswap_debugfs_init())
                pr_warn("debugfs initialization failed\n");
        return 0;
 
+destroy_wq:
+       destroy_workqueue(shrink_wq);
 fallback_fail:
        if (pool)
                zswap_pool_destroy(pool);