We wish for transcendent memory backends to be able to push
frontswap pages back into the swap cache and need to ensure
that such a page, once pushed back, doesn't get immediately
recaptured by frontswap. We add frontswap_unuse to do the
pushing via the recently added read_frontswap_async. We
also add metadata to track when a page has been pushed and
code to manage (and count with debugfs) this metadata.
The initialization/destruction code for the metadata (aka
frontswap_denial_map) is a bit clunky in swapfile.c but
cleanup can be addressed when all the unuse code is working.
Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
---
include/linux/frontswap.h | 57 +++++++++++++++++++++++++++++++++++++++++++++
include/linux/swap.h | 1 +
mm/frontswap.c | 29 +++++++++++++++++++++++
mm/swapfile.c | 18 ++++++++++----
4 files changed, 100 insertions(+), 5 deletions(-)
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index 3044254..f48bb34 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -21,6 +21,8 @@ extern unsigned long frontswap_curr_pages(void);
extern void frontswap_writethrough(bool);
#define FRONTSWAP_HAS_EXCLUSIVE_GETS
extern void frontswap_tmem_exclusive_gets(bool);
+#define FRONTSWAP_HAS_UNUSE
+extern int frontswap_unuse(int, pgoff_t, struct page *, gfp_t);
extern void __frontswap_init(unsigned type);
extern int __frontswap_store(struct page *page);
@@ -61,6 +63,38 @@ static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
{
return p->frontswap_map;
}
+
+static inline int frontswap_test_denial(struct swap_info_struct *sis, pgoff_t offset)
+{
+ int ret = 0;
+
+ if (frontswap_enabled && sis->frontswap_denial_map)
+ ret = test_bit(offset, sis->frontswap_denial_map);
+ return ret;
+}
+
+static inline void frontswap_set_denial(struct swap_info_struct *sis, pgoff_t offset)
+{
+ if (frontswap_enabled && sis->frontswap_denial_map)
+ set_bit(offset, sis->frontswap_denial_map);
+}
+
+static inline void frontswap_clear_denial(struct swap_info_struct *sis, pgoff_t offset)
+{
+ if (frontswap_enabled && sis->frontswap_denial_map)
+ clear_bit(offset, sis->frontswap_denial_map);
+}
+
+static inline void frontswap_denial_map_set(struct swap_info_struct *p,
+ unsigned long *map)
+{
+ p->frontswap_denial_map = map;
+}
+
+static inline unsigned long *frontswap_denial_map_get(struct swap_info_struct *p)
+{
+ return p->frontswap_denial_map;
+}
#else
/* all inline routines become no-ops and all externs are ignored */
@@ -88,6 +122,29 @@ static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
{
return NULL;
}
+
+static inline int frontswap_test_denial(struct swap_info_struct *sis, pgoff_t offset)
+{
+ return 0;
+}
+
+static inline void frontswap_set_denial(struct swap_info_struct *sis, pgoff_t offset)
+{
+}
+
+static inline void frontswap_clear_denial(struct swap_info_struct *sis, pgoff_t offset)
+{
+}
+
+static inline void frontswap_map_set_denial(struct swap_info_struct *p,
+ unsigned long *map)
+{
+}
+
+static inline unsigned long *frontswap_map_get_denial(struct swap_info_struct *p)
+{
+ return NULL;
+}
#endif
static inline int frontswap_store(struct page *page)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8a59ddb..aef02bc 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -200,6 +200,7 @@ struct swap_info_struct {
unsigned int old_block_size; /* seldom referenced */
#ifdef CONFIG_FRONTSWAP
unsigned long *frontswap_map; /* frontswap in-use, one bit per page */
+ unsigned long *frontswap_denial_map; /* deny frontswap, 1bit/page */
atomic_t frontswap_pages; /* frontswap pages in-use counter */
#endif
};
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 2890e67..1af07d1 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -61,6 +61,8 @@ static u64 frontswap_loads;
static u64 frontswap_succ_stores;
static u64 frontswap_failed_stores;
static u64 frontswap_invalidates;
+static u64 frontswap_unuses;
+static u64 frontswap_denials;
static inline void inc_frontswap_loads(void) {
frontswap_loads++;
@@ -151,6 +153,11 @@ int __frontswap_store(struct page *page)
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset))
dup = 1;
+ if (frontswap_test_denial(sis, offset) && (dup == 0)) {
+ frontswap_clear_denial(sis, offset);
+ frontswap_denials++;
+ goto out;
+ }
ret = frontswap_ops.store(type, offset, page);
if (ret == 0) {
frontswap_set(sis, offset);
@@ -169,6 +176,7 @@ int __frontswap_store(struct page *page)
if (frontswap_writethrough_enabled)
/* report failure so swap also writes to swap device */
ret = -1;
+out:
return ret;
}
EXPORT_SYMBOL(__frontswap_store);
@@ -213,6 +221,7 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
if (frontswap_test(sis, offset)) {
frontswap_ops.invalidate_page(type, offset);
__frontswap_clear(sis, offset);
+ frontswap_clear_denial(sis, offset);
inc_frontswap_invalidates();
}
}
@@ -351,6 +360,24 @@ unsigned long frontswap_curr_pages(void)
}
EXPORT_SYMBOL(frontswap_curr_pages);
+int frontswap_unuse(int type, pgoff_t offset,
+ struct page *newpage, gfp_t gfp_mask)
+{
+ struct swap_info_struct *sis = swap_info[type];
+ int ret = 0;
+
+ frontswap_set_denial(sis, offset);
+ ret = read_frontswap_async(type, offset, newpage, gfp_mask);
+ if (ret == 0 || ret == -EEXIST) {
+ (*frontswap_ops.invalidate_page)(type, offset);
+ atomic_dec(&sis->frontswap_pages);
+ frontswap_clear(sis, offset);
+ frontswap_unuses++;
+ }
+ return ret;
+}
+EXPORT_SYMBOL(frontswap_unuse);
+
static int __init init_frontswap(void)
{
#ifdef CONFIG_DEBUG_FS
@@ -363,6 +390,8 @@ static int __init init_frontswap(void)
&frontswap_failed_stores);
debugfs_create_u64("invalidates", S_IRUGO,
root, &frontswap_invalidates);
+ debugfs_create_u64("unuses", S_IRUGO, root, &frontswap_unuses);
+ debugfs_create_u64("denials", S_IRUGO, root, &frontswap_denials);
#endif
return 0;
}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 14e254c..b3d6266 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1445,7 +1445,8 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
static void enable_swap_info(struct swap_info_struct *p, int prio,
unsigned char *swap_map,
- unsigned long *frontswap_map)
+ unsigned long *frontswap_map,
+ unsigned long *frontswap_denial_map)
{
int i, prev;
@@ -1456,6 +1457,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
p->prio = --least_priority;
p->swap_map = swap_map;
frontswap_map_set(p, frontswap_map);
+ frontswap_denial_map_set(p, frontswap_denial_map);
p->flags |= SWP_WRITEOK;
nr_swap_pages += p->pages;
total_swap_pages += p->pages;
@@ -1557,7 +1559,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
* sys_swapoff for this swap_info_struct at this point.
*/
/* re-insert swap space back into swap_list */
- enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
+ enable_swap_info(p, p->prio, p->swap_map,
+ frontswap_map_get(p), frontswap_denial_map_get(p));
goto out_dput;
}
@@ -1588,6 +1591,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
mutex_unlock(&swapon_mutex);
vfree(swap_map);
vfree(frontswap_map_get(p));
+ vfree(frontswap_denial_map_get(p));
/* Destroy swap account informatin */
swap_cgroup_swapoff(type);
@@ -1948,6 +1952,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
unsigned long maxpages;
unsigned char *swap_map = NULL;
unsigned long *frontswap_map = NULL;
+ unsigned long *frontswap_denial_map = NULL;
struct page *page = NULL;
struct inode *inode = NULL;
@@ -2032,8 +2037,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
goto bad_swap;
}
/* frontswap enabled? set up bit-per-page map for frontswap */
- if (frontswap_enabled)
- frontswap_map = vzalloc(maxpages / sizeof(long));
+ if (frontswap_enabled) {
+ frontswap_map = vzalloc(maxpages / sizeof(long));
+ frontswap_denial_map = vzalloc(maxpages / sizeof(long));
+ }
if (p->bdev) {
if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
@@ -2049,7 +2056,8 @@ 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, frontswap_map);
+ enable_swap_info(p, prio, swap_map,
+ frontswap_map, frontswap_denial_map);
printk(KERN_INFO "Adding %uk swap on %s. "
"Priority:%d extents:%d across:%lluk %s%s%s\n",
--
1.7.1
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