With the goal of allowing tmem backends (zcache, ramster, Xen tmem) to be
built/loaded as modules rather than built-in and enabled by a boot parameter,
this patch provides "lazy initialization", allowing backends to register to
frontswap even after swapon was run. Before a backend registers all calls
to init are recorded and the creation of tmem_pools delayed until a backend
registers or until a frontswap put is attempted.
Signed-off-by: Stefan Hengelein <ilendir@xxxxxxxxxxxxxx>
Signed-off-by: Florian Schmaus <fschmaus@xxxxxxxxx>
Signed-off-by: Andor Daam <andor.daam@xxxxxxxxxxxxxx>
Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
---
include/linux/frontswap.h | 1 +
mm/frontswap.c | 70 +++++++++++++++++++++++++++++++++++++++-----
2 files changed, 63 insertions(+), 8 deletions(-)
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index 3044254..ef6ada6 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -23,6 +23,7 @@ extern void frontswap_writethrough(bool);
extern void frontswap_tmem_exclusive_gets(bool);
extern void __frontswap_init(unsigned type);
+#define FRONTSWAP_HAS_LAZY_INIT
extern int __frontswap_store(struct page *page);
extern int __frontswap_load(struct page *page);
extern void __frontswap_invalidate_page(unsigned, pgoff_t);
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 2890e67..523a19b 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -80,6 +80,19 @@ static inline void inc_frontswap_succ_stores(void) { }
static inline void inc_frontswap_failed_stores(void) { }
static inline void inc_frontswap_invalidates(void) { }
#endif
+
+/*
+ * When no backend is registered all calls to init are registered and
+ * remembered but fail to create tmem_pools. When a backend registers with
+ * frontswap the previous calls to init are executed to create tmem_pools
+ * and set the respective poolids.
+ * While no backend is registered all "puts", "gets" and "flushes" are
+ * ignored or fail.
+ */
+#define MAX_INITIALIZABLE_SD 32
+static int sds[MAX_INITIALIZABLE_SD];
+static int backend_registered;
+
/*
* Register operations for frontswap, returning previous thus allowing
* detection of multiple backends and possible nesting.
@@ -87,9 +100,16 @@ static inline void inc_frontswap_invalidates(void) { }
struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
{
struct frontswap_ops old = frontswap_ops;
+ int i;
frontswap_ops = *ops;
frontswap_enabled = true;
+
+ backend_registered = 1;
+ for (i = 0; i < MAX_INITIALIZABLE_SD; i++) {
+ if (sds[i] != -1)
+ (*frontswap_ops.init)(sds[i]);
+ }
return old;
}
EXPORT_SYMBOL(frontswap_register_ops);
@@ -122,7 +142,10 @@ void __frontswap_init(unsigned type)
BUG_ON(sis == NULL);
if (sis->frontswap_map == NULL)
return;
- frontswap_ops.init(type);
+ if (backend_registered) {
+ (*frontswap_ops.init)(type);
+ sds[type] = type;
+ }
}
EXPORT_SYMBOL(__frontswap_init);
@@ -147,10 +170,20 @@ int __frontswap_store(struct page *page)
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
+ if (!backend_registered) {
+ inc_frontswap_failed_stores();
+ return ret;
+ }
+
BUG_ON(!PageLocked(page));
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset))
dup = 1;
+ if (type < MAX_INITIALIZABLE_SD && sds[type] == -1) {
+ /* lazy init call to handle post-boot insmod backends*/
+ (*frontswap_ops.init)(type);
+ sds[type] = type;
+ }
ret = frontswap_ops.store(type, offset, page);
if (ret == 0) {
frontswap_set(sis, offset);
@@ -186,6 +219,9 @@ int __frontswap_load(struct page *page)
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
+ if (!backend_registered)
+ return ret;
+
BUG_ON(!PageLocked(page));
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset))
@@ -209,6 +245,9 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
{
struct swap_info_struct *sis = swap_info[type];
+ if (!backend_registered)
+ return;
+
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset)) {
frontswap_ops.invalidate_page(type, offset);
@@ -225,13 +264,23 @@ EXPORT_SYMBOL(__frontswap_invalidate_page);
void __frontswap_invalidate_area(unsigned type)
{
struct swap_info_struct *sis = swap_info[type];
-
- BUG_ON(sis == NULL);
- if (sis->frontswap_map == NULL)
- return;
- frontswap_ops.invalidate_area(type);
- atomic_set(&sis->frontswap_pages, 0);
- memset(sis->frontswap_map, 0, sis->max / sizeof(long));
+ int i;
+
+ if (backend_registered) {
+ BUG_ON(sis == NULL);
+ if (sis->frontswap_map == NULL)
+ return;
+ (*frontswap_ops.invalidate_area)(type);
+ atomic_set(&sis->frontswap_pages, 0);
+ memset(sis->frontswap_map, 0, sis->max / sizeof(long));
+ } else {
+ for (i = 0; i < MAX_INITIALIZABLE_SD; i++) {
+ if (sds[i] == type) {
+ sds[i] = -1;
+ break;
+ }
+ }
+ }
}
EXPORT_SYMBOL(__frontswap_invalidate_area);
@@ -353,6 +402,7 @@ EXPORT_SYMBOL(frontswap_curr_pages);
static int __init init_frontswap(void)
{
+ int i;
#ifdef CONFIG_DEBUG_FS
struct dentry *root = debugfs_create_dir("frontswap", NULL);
if (root == NULL)
@@ -364,6 +414,10 @@ static int __init init_frontswap(void)
debugfs_create_u64("invalidates", S_IRUGO,
root, &frontswap_invalidates);
#endif
+ for (i = 0; i < MAX_INITIALIZABLE_SD; i++)
+ sds[i] = -1;
+
+ frontswap_enabled = 1;
return 0;
}
--
1.7.1
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