mm: frontswap: core swap subsystem hooks and headers

This patch, 2of4, contains the changes to the core swap subsystem.
This includes:

(1) makes available core swap data structures (swap_lock, swap_list and
swap_info) that are needed by frontswap.c but we don't need to expose them
to the dozens of files that include swap.h so we create a new swapfile.h
just to extern-ify these and modify their declarations to non-static

(2) adds frontswap-related elements to swap_info_struct.  Frontswap_map
points to vzalloc'ed one-bit-per-swap-page metadata that indicates
whether the swap page is in frontswap or in the device and frontswap_pages
counts how many pages are in frontswap.

(3) adds hooks in the swap subsystem and extends try_to_unuse so that
frontswap_shrink can do a "partial swapoff".

Note that a failed frontswap_map allocation is safe... failure is noted
by lack of "FS" in the subsequent printk.

---

[v14: rebase to 3.4-rc2]
[v10: no change]
[v9: akpm@linux-foundation.org: mark some statics __read_mostly]
[v9: akpm@linux-foundation.org: add clarifying comments]
[v9: akpm@linux-foundation.org: no need to loop repeating try_to_unuse]
[v9: error27@gmail.com: remove superfluous check for NULL]
[v8: rebase to 3.0-rc4]
[v8: kamezawa.hiroyu@jp.fujitsu.com: change counter to atomic_t to avoid races]
[v8: kamezawa.hiroyu@jp.fujitsu.com: comment to clarify informational counters]
[v7: rebase to 3.0-rc3]
[v7: JBeulich@novell.com: add new swap struct elements only if config'd]
[v6: rebase to 3.0-rc1]
[v6: lliubbo@gmail.com: fix null pointer deref if vzalloc fails]
[v6: konrad.wilk@oracl.com: various checks and code clarifications/comments]
[v5: no change from v4]
[v4: rebase to 2.6.39]
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Reviewed-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Jan Beulich <JBeulich@novell.com>
Acked-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Rik Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
[v11: Rebased, fixed mm/swapfile.c context change]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

2 files changed, 53 insertions, 13 deletions

diff --git a/mm/page_io.c b/mm/page_io.c
index dc76b4d0611e..651a91259317 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_put_page(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_get_page(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 fafc26d1b1dc..9c7be87175c5 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);
@@ -1016,11 +1019,12 @@ 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;
@@ -1046,6 +1050,12 @@ 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;
@@ -1057,8 +1067,12 @@ 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;
@@ -1091,7 +1105,7 @@ 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;
@@ -1258,6 +1272,10 @@ 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);
@@ -1517,7 +1535,8 @@ 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;
 
@@ -1527,6 +1546,7 @@ 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;
@@ -1543,6 +1563,7 @@ 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);
 }
 
@@ -1616,7 +1637,7 @@ 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) {
@@ -1627,7 +1648,7 @@ 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;
         }
 
@@ -1653,9 +1674,11 @@ 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);
 
@@ -2019,6 +2042,7 @@ 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;
 
@@ -2102,6 +2126,9 @@ 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))) {
@@ -2117,14 +2144,15 @@ 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);