From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
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>
[v1: Fixes per Seth Jennings suggestions]
[v2: Removed FRONTSWAP_HAS_.. ]
[v3: Fix up per Bob Liu <lliubbo@xxxxxxxxx> recommendations]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
mm/frontswap.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++--------
1 files changed, 56 insertions(+), 10 deletions(-)
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 2890e67..ba58157 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -80,6 +80,18 @@ 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.
+ */
+static DECLARE_BITMAP(need_init, MAX_SWAPFILES);
+static bool backend_registered __read_mostly;
+
/*
* Register operations for frontswap, returning previous thus allowing
* detection of multiple backends and possible nesting.
@@ -87,9 +99,19 @@ 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;
+
+ for (i = 0; i < MAX_SWAPFILES; i++) {
+ if (test_and_clear_bit(i, need_init))
+ (*frontswap_ops.init)(i);
+ }
+ /* We MUST have backend_registered called _after_ the frontswap_init's
+ * have been called. Otherwise __frontswap_store might fail. */
+ barrier();
+ backend_registered = true;
return old;
}
EXPORT_SYMBOL(frontswap_register_ops);
@@ -119,10 +141,17 @@ void __frontswap_init(unsigned type)
{
struct swap_info_struct *sis = swap_info[type];
- BUG_ON(sis == NULL);
- if (sis->frontswap_map == NULL)
- return;
- frontswap_ops.init(type);
+ if (backend_registered) {
+ BUG_ON(sis == NULL);
+ if (sis->frontswap_map == NULL)
+ return;
+ (*frontswap_ops.init)(type);
+ }
+ else {
+ BUG_ON(type > MAX_SWAPFILES);
+ set_bit(type, need_init);
+ }
+
}
EXPORT_SYMBOL(__frontswap_init);
@@ -147,6 +176,11 @@ 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))
@@ -186,6 +220,9 @@ 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 +246,9 @@ 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);
@@ -226,12 +266,15 @@ 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));
+ 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));
+ }
+ clear_bit(type, need_init);
}
EXPORT_SYMBOL(__frontswap_invalidate_area);
@@ -364,6 +407,9 @@ static int __init init_frontswap(void)
debugfs_create_u64("invalidates", S_IRUGO,
root, &frontswap_invalidates);
#endif
+ bitmap_zero(need_init, MAX_SWAPFILES);
+
+ frontswap_enabled = 1;
return 0;
}
--
1.7.7.6
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>