5 files changed, 385 insertions, 13 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index b2176374b98e..82fed4eb2b6f 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -389,3 +389,20 @@ config CLEANCACHE
           in a negligible performance hit.
 
           If unsure, say Y to enable cleancache
+
+config FRONTSWAP
+        bool "Enable frontswap to cache swap pages if tmem is present"
+        depends on SWAP
+        default n
+        help
+          Frontswap is so named because it can be thought of as the opposite
+          of a "backing" store for a swap device.  The data is stored into
+          "transcendent memory", memory that is not directly accessible or
+          addressable by the kernel and is of unknown and possibly
+          time-varying size.  When space in transcendent memory is available,
+          a significant swap I/O reduction may be achieved.  When none is
+          available, all frontswap calls are reduced to a single pointer-
+          compare-against-NULL resulting in a negligible performance hit
+          and swap data is stored as normal on the matching swap device.
+
+          If unsure, say Y to enable frontswap.
diff --git a/mm/Makefile b/mm/Makefile
index a156285ce88d..2e2fbbefb99f 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -29,6 +29,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
 
 obj-$(CONFIG_BOUNCE)    += bounce.o
 obj-$(CONFIG_SWAP)      += page_io.o swap_state.o swapfile.o
+obj-$(CONFIG_FRONTSWAP) += frontswap.o
 obj-$(CONFIG_HAS_DMA)   += dmapool.o
 obj-$(CONFIG_HUGETLBFS) += hugetlb.o
 obj-$(CONFIG_NUMA)      += mempolicy.o
diff --git a/mm/frontswap.c b/mm/frontswap.c
new file mode 100644
index 000000000000..e25025574a02
--- /dev/null
+++ b/mm/frontswap.c
@@ -0,0 +1,314 @@
+/*
+ * Frontswap frontend
+ *
+ * This code provides the generic "frontend" layer to call a matching
+ * "backend" driver implementation of frontswap.  See
+ * Documentation/vm/frontswap.txt for more information.
+ *
+ * Copyright (C) 2009-2012 Oracle Corp.  All rights reserved.
+ * Author: Dan Magenheimer
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ */
+
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/proc_fs.h>
+#include <linux/security.h>
+#include <linux/capability.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/debugfs.h>
+#include <linux/frontswap.h>
+#include <linux/swapfile.h>
+
+/*
+ * frontswap_ops is set by frontswap_register_ops to contain the pointers
+ * to the frontswap "backend" implementation functions.
+ */
+static struct frontswap_ops frontswap_ops __read_mostly;
+
+/*
+ * This global enablement flag reduces overhead on systems where frontswap_ops
+ * has not been registered, so is preferred to the slower alternative: a
+ * function call that checks a non-global.
+ */
+bool frontswap_enabled __read_mostly;
+EXPORT_SYMBOL(frontswap_enabled);
+
+/*
+ * If enabled, frontswap_store will return failure even on success.  As
+ * a result, the swap subsystem will always write the page to swap, in
+ * effect converting frontswap into a writethrough cache.  In this mode,
+ * there is no direct reduction in swap writes, but a frontswap backend
+ * can unilaterally "reclaim" any pages in use with no data loss, thus
+ * providing increases control over maximum memory usage due to frontswap.
+ */
+static bool frontswap_writethrough_enabled __read_mostly;
+
+#ifdef CONFIG_DEBUG_FS
+/*
+ * Counters available via /sys/kernel/debug/frontswap (if debugfs is
+ * properly configured).  These are for information only so are not protected
+ * against increment races.
+ */
+static u64 frontswap_loads;
+static u64 frontswap_succ_stores;
+static u64 frontswap_failed_stores;
+static u64 frontswap_invalidates;
+
+static inline void inc_frontswap_loads(void) {
+        frontswap_loads++;
+}
+static inline void inc_frontswap_succ_stores(void) {
+        frontswap_succ_stores++;
+}
+static inline void inc_frontswap_failed_stores(void) {
+        frontswap_failed_stores++;
+}
+static inline void inc_frontswap_invalidates(void) {
+        frontswap_invalidates++;
+}
+#else
+static inline void inc_frontswap_loads(void) { }
+static inline void inc_frontswap_succ_stores(void) { }
+static inline void inc_frontswap_failed_stores(void) { }
+static inline void inc_frontswap_invalidates(void) { }
+#endif
+/*
+ * Register operations for frontswap, returning previous thus allowing
+ * detection of multiple backends and possible nesting.
+ */
+struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
+{
+        struct frontswap_ops old = frontswap_ops;
+
+        frontswap_ops = *ops;
+        frontswap_enabled = true;
+        return old;
+}
+EXPORT_SYMBOL(frontswap_register_ops);
+
+/*
+ * Enable/disable frontswap writethrough (see above).
+ */
+void frontswap_writethrough(bool enable)
+{
+        frontswap_writethrough_enabled = enable;
+}
+EXPORT_SYMBOL(frontswap_writethrough);
+
+/*
+ * Called when a swap device is swapon'd.
+ */
+void __frontswap_init(unsigned type)
+{
+        struct swap_info_struct *sis = swap_info[type];
+
+        BUG_ON(sis == NULL);
+        if (sis->frontswap_map == NULL)
+                return;
+        if (frontswap_enabled)
+                (*frontswap_ops.init)(type);
+}
+EXPORT_SYMBOL(__frontswap_init);
+
+/*
+ * "Store" data from a page to frontswap and associate it with the page's
+ * swaptype and offset.  Page must be locked and in the swap cache.
+ * If frontswap already contains a page with matching swaptype and
+ * offset, the frontswap implmentation may either overwrite the data and
+ * return success or invalidate the page from frontswap and return failure.
+ */
+int __frontswap_store(struct page *page)
+{
+        int ret = -1, dup = 0;
+        swp_entry_t entry = { .val = page_private(page), };
+        int type = swp_type(entry);
+        struct swap_info_struct *sis = swap_info[type];
+        pgoff_t offset = swp_offset(entry);
+
+        BUG_ON(!PageLocked(page));
+        BUG_ON(sis == NULL);
+        if (frontswap_test(sis, offset))
+                dup = 1;
+        ret = (*frontswap_ops.store)(type, offset, page);
+        if (ret == 0) {
+                frontswap_set(sis, offset);
+                inc_frontswap_succ_stores();
+                if (!dup)
+                        atomic_inc(&sis->frontswap_pages);
+        } else if (dup) {
+                /*
+                  failed dup always results in automatic invalidate of
+                  the (older) page from frontswap
+                 */
+                frontswap_clear(sis, offset);
+                atomic_dec(&sis->frontswap_pages);
+                inc_frontswap_failed_stores();
+        } else
+                inc_frontswap_failed_stores();
+        if (frontswap_writethrough_enabled)
+                /* report failure so swap also writes to swap device */
+                ret = -1;
+        return ret;
+}
+EXPORT_SYMBOL(__frontswap_store);
+
+/*
+ * "Get" data from frontswap associated with swaptype and offset that were
+ * specified when the data was put to frontswap and use it to fill the
+ * specified page with data. Page must be locked and in the swap cache.
+ */
+int __frontswap_load(struct page *page)
+{
+        int ret = -1;
+        swp_entry_t entry = { .val = page_private(page), };
+        int type = swp_type(entry);
+        struct swap_info_struct *sis = swap_info[type];
+        pgoff_t offset = swp_offset(entry);
+
+        BUG_ON(!PageLocked(page));
+        BUG_ON(sis == NULL);
+        if (frontswap_test(sis, offset))
+                ret = (*frontswap_ops.load)(type, offset, page);
+        if (ret == 0)
+                inc_frontswap_loads();
+        return ret;
+}
+EXPORT_SYMBOL(__frontswap_load);
+
+/*
+ * Invalidate any data from frontswap associated with the specified swaptype
+ * and offset so that a subsequent "get" will fail.
+ */
+void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
+{
+        struct swap_info_struct *sis = swap_info[type];
+
+        BUG_ON(sis == NULL);
+        if (frontswap_test(sis, offset)) {
+                (*frontswap_ops.invalidate_page)(type, offset);
+                atomic_dec(&sis->frontswap_pages);
+                frontswap_clear(sis, offset);
+                inc_frontswap_invalidates();
+        }
+}
+EXPORT_SYMBOL(__frontswap_invalidate_page);
+
+/*
+ * Invalidate all data from frontswap associated with all offsets for the
+ * specified swaptype.
+ */
+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));
+}
+EXPORT_SYMBOL(__frontswap_invalidate_area);
+
+/*
+ * Frontswap, like a true swap device, may unnecessarily retain pages
+ * under certain circumstances; "shrink" frontswap is essentially a
+ * "partial swapoff" and works by calling try_to_unuse to attempt to
+ * unuse enough frontswap pages to attempt to -- subject to memory
+ * constraints -- reduce the number of pages in frontswap to the
+ * number given in the parameter target_pages.
+ */
+void frontswap_shrink(unsigned long target_pages)
+{
+        struct swap_info_struct *si = NULL;
+        int si_frontswap_pages;
+        unsigned long total_pages = 0, total_pages_to_unuse;
+        unsigned long pages = 0, pages_to_unuse = 0;
+        int type;
+        bool locked = false;
+
+        /*
+         * we don't want to hold swap_lock while doing a very
+         * lengthy try_to_unuse, but swap_list may change
+         * so restart scan from swap_list.head each time
+         */
+        spin_lock(&swap_lock);
+        locked = true;
+        total_pages = 0;
+        for (type = swap_list.head; type >= 0; type = si->next) {
+                si = swap_info[type];
+                total_pages += atomic_read(&si->frontswap_pages);
+        }
+        if (total_pages <= target_pages)
+                goto out;
+        total_pages_to_unuse = total_pages - target_pages;
+        for (type = swap_list.head; type >= 0; type = si->next) {
+                si = swap_info[type];
+                si_frontswap_pages = atomic_read(&si->frontswap_pages);
+                if (total_pages_to_unuse < si_frontswap_pages)
+                        pages = pages_to_unuse = total_pages_to_unuse;
+                else {
+                        pages = si_frontswap_pages;
+                        pages_to_unuse = 0; /* unuse all */
+                }
+                /* ensure there is enough RAM to fetch pages from frontswap */
+                if (security_vm_enough_memory_mm(current->mm, pages))
+                        continue;
+                vm_unacct_memory(pages);
+                break;
+        }
+        if (type < 0)
+                goto out;
+        locked = false;
+        spin_unlock(&swap_lock);
+        try_to_unuse(type, true, pages_to_unuse);
+out:
+        if (locked)
+                spin_unlock(&swap_lock);
+        return;
+}
+EXPORT_SYMBOL(frontswap_shrink);
+
+/*
+ * Count and return the number of frontswap pages across all
+ * swap devices.  This is exported so that backend drivers can
+ * determine current usage without reading debugfs.
+ */
+unsigned long frontswap_curr_pages(void)
+{
+        int type;
+        unsigned long totalpages = 0;
+        struct swap_info_struct *si = NULL;
+
+        spin_lock(&swap_lock);
+        for (type = swap_list.head; type >= 0; type = si->next) {
+                si = swap_info[type];
+                totalpages += atomic_read(&si->frontswap_pages);
+        }
+        spin_unlock(&swap_lock);
+        return totalpages;
+}
+EXPORT_SYMBOL(frontswap_curr_pages);
+
+static int __init init_frontswap(void)
+{
+#ifdef CONFIG_DEBUG_FS
+        struct dentry *root = debugfs_create_dir("frontswap", NULL);
+        if (root == NULL)
+                return -ENXIO;
+        debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
+        debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
+        debugfs_create_u64("failed_stores", S_IRUGO, root,
+                                &frontswap_failed_stores);
+        debugfs_create_u64("invalidates", S_IRUGO,
+                                root, &frontswap_invalidates);
+#endif
+        return 0;
+}
+
+module_init(init_frontswap);
diff --git a/mm/page_io.c b/mm/page_io.c
index dc76b4d0611e..34f02923744c 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -18,6 +18,7 @@
 #include <linux/bio.h>
 #include <linux/swapops.h>
 #include <linux/writeback.h>
+#include <linux/frontswap.h>
 #include <asm/pgtable.h>
 
 static struct bio *get_swap_bio(gfp_t gfp_flags,
@@ -98,6 +99,12 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
                 unlock_page(page);
                 goto out;
         }
+        if (frontswap_store(page) == 0) {
+                set_page_writeback(page);
+                unlock_page(page);
+                end_page_writeback(page);
+                goto out;
+        }
         bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
         if (bio == NULL) {
                 set_page_dirty(page);
@@ -122,6 +129,11 @@ int swap_readpage(struct page *page)
 
         VM_BUG_ON(!PageLocked(page));
         VM_BUG_ON(PageUptodate(page));
+        if (frontswap_load(page) == 0) {
+                SetPageUptodate(page);
+                unlock_page(page);
+                goto out;
+        }
         bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
         if (bio == NULL) {
                 unlock_page(page);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 457b10baef59..de5bc51c4a66 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -31,6 +31,8 @@
 #include <linux/memcontrol.h>
 #include <linux/poll.h>
 #include <linux/oom.h>
+#include <linux/frontswap.h>
+#include <linux/swapfile.h>
 
 #include <asm/pgtable.h>
 #include <asm/tlbflush.h>
@@ -42,7 +44,7 @@ static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
 static void free_swap_count_continuations(struct swap_info_struct *);
 static sector_t map_swap_entry(swp_entry_t, struct block_device**);
 
-static DEFINE_SPINLOCK(swap_lock);
+DEFINE_SPINLOCK(swap_lock);
 static unsigned int nr_swapfiles;
 long nr_swap_pages;
 long total_swap_pages;
@@ -53,9 +55,9 @@ static const char Unused_file[] = "Unused swap file entry ";
 static const char Bad_offset[] = "Bad swap offset entry ";
 static const char Unused_offset[] = "Unused swap offset entry ";
 
-static struct swap_list_t swap_list = {-1, -1};
+struct swap_list_t swap_list = {-1, -1};
 
-static struct swap_info_struct *swap_info[MAX_SWAPFILES];
+struct swap_info_struct *swap_info[MAX_SWAPFILES];
 
 static DEFINE_MUTEX(swapon_mutex);
 
@@ -556,6 +558,7 @@ static unsigned char swap_entry_free(struct swap_info_struct *p,
                         swap_list.next = p->type;
                 nr_swap_pages++;
                 p->inuse_pages--;
+                frontswap_invalidate_page(p->type, offset);
                 if ((p->flags & SWP_BLKDEV) &&
                                 disk->fops->swap_slot_free_notify)
                         disk->fops->swap_slot_free_notify(p->bdev, offset);
@@ -985,11 +988,12 @@ static int unuse_mm(struct mm_struct *mm,
 }
 
 /*
- * Scan swap_map from current position to next entry still in use.
+ * Scan swap_map (or frontswap_map if frontswap parameter is true)
+ * from current position to next entry still in use.
  * Recycle to start on reaching the end, returning 0 when empty.
  */
 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
-                                        unsigned int prev)
+                                        unsigned int prev, bool frontswap)
 {
         unsigned int max = si->max;
         unsigned int i = prev;
@@ -1015,6 +1019,12 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
                         prev = 0;
                         i = 1;
                 }
+                if (frontswap) {
+                        if (frontswap_test(si, i))
+                                break;
+                        else
+                                continue;
+                }
                 count = si->swap_map[i];
                 if (count && swap_count(count) != SWAP_MAP_BAD)
                         break;
@@ -1026,8 +1036,12 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
  * We completely avoid races by reading each swap page in advance,
  * and then search for the process using it.  All the necessary
  * page table adjustments can then be made atomically.
+ *
+ * if the boolean frontswap is true, only unuse pages_to_unuse pages;
+ * pages_to_unuse==0 means all pages; ignored if frontswap is false
  */
-static int try_to_unuse(unsigned int type)
+int try_to_unuse(unsigned int type, bool frontswap,
+                 unsigned long pages_to_unuse)
 {
         struct swap_info_struct *si = swap_info[type];
         struct mm_struct *start_mm;
@@ -1060,7 +1074,7 @@ static int try_to_unuse(unsigned int type)
          * one pass through swap_map is enough, but not necessarily:
          * there are races when an instance of an entry might be missed.
          */
-        while ((i = find_next_to_unuse(si, i)) != 0) {
+        while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
                 if (signal_pending(current)) {
                         retval = -EINTR;
                         break;
@@ -1227,6 +1241,10 @@ static int try_to_unuse(unsigned int type)
                  * interactive performance.
                  */
                 cond_resched();
+                if (frontswap && pages_to_unuse > 0) {
+                        if (!--pages_to_unuse)
+                                break;
+                }
         }
 
         mmput(start_mm);
@@ -1486,7 +1504,8 @@ bad_bmap:
 }
 
 static void enable_swap_info(struct swap_info_struct *p, int prio,
-                                unsigned char *swap_map)
+                                unsigned char *swap_map,
+                                unsigned long *frontswap_map)
 {
         int i, prev;
 
@@ -1496,6 +1515,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
         else
                 p->prio = --least_priority;
         p->swap_map = swap_map;
+        frontswap_map_set(p, frontswap_map);
         p->flags |= SWP_WRITEOK;
         nr_swap_pages += p->pages;
         total_swap_pages += p->pages;
@@ -1512,6 +1532,7 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
                 swap_list.head = swap_list.next = p->type;
         else
                 swap_info[prev]->next = p->type;
+        frontswap_init(p->type);
         spin_unlock(&swap_lock);
 }
 
@@ -1585,7 +1606,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
         spin_unlock(&swap_lock);
 
         oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
-        err = try_to_unuse(type);
+        err = try_to_unuse(type, false, 0); /* force all pages to be unused */
         compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX, oom_score_adj);
 
         if (err) {
@@ -1596,7 +1617,7 @@ 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);
+                enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
                 goto out_dput;
         }
 
@@ -1622,9 +1643,11 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
         swap_map = p->swap_map;
         p->swap_map = NULL;
         p->flags = 0;
+        frontswap_invalidate_area(type);
         spin_unlock(&swap_lock);
         mutex_unlock(&swapon_mutex);
         vfree(swap_map);
+        vfree(frontswap_map_get(p));
         /* Destroy swap account informatin */
         swap_cgroup_swapoff(type);
 
@@ -1988,6 +2011,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
         sector_t span;
         unsigned long maxpages;
         unsigned char *swap_map = NULL;
+        unsigned long *frontswap_map = NULL;
         struct page *page = NULL;
         struct inode *inode = NULL;
 
@@ -2071,6 +2095,9 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
                 error = nr_extents;
                 goto bad_swap;
         }
+        /* frontswap enabled? set up bit-per-page map for frontswap */
+        if (frontswap_enabled)
+                frontswap_map = vzalloc(maxpages / sizeof(long));
 
         if (p->bdev) {
                 if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
@@ -2086,14 +2113,15 @@ 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);
+        enable_swap_info(p, prio, swap_map, frontswap_map);
 
         printk(KERN_INFO "Adding %uk swap on %s.  "
-                        "Priority:%d extents:%d across:%lluk %s%s\n",
+                        "Priority:%d extents:%d across:%lluk %s%s%s\n",
                 p->pages<<(PAGE_SHIFT-10), name, p->prio,
                 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
                 (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
-                (p->flags & SWP_DISCARDABLE) ? "D" : "");
+                (p->flags & SWP_DISCARDABLE) ? "D" : "",
+                (frontswap_map) ? "FS" : "");
 
         mutex_unlock(&swapon_mutex);
         atomic_inc(&proc_poll_event);