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Date: Wed, 3 Oct 2012 15:43:54 -0700
From: Dan Magenheimer <dan.magenheimer@...cle.com>
To: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
ngupta@...are.org, konrad.wilk@...cle.com,
sjenning@...ux.vnet.ibm.com, minchan@...nel.org, hughd@...gle.com,
akpm@...ux-foundation.org, riel@...hat.com, hannes@...xchg.org,
dan.magenheimer@...cle.com, aarcange@...hat.com, mgorman@...e.de,
gregkh@...uxfoundation.org
Subject: [RFC/PATCH 3/3] frontswap/swap: allow frontswap "unuse" and add metadata for tracking it
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@...cle.com>
---
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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