2 files changed, 102 insertions, 34 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8a3c4a1caa14..24db9142e93b 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -199,6 +199,16 @@ struct swap_cluster_info {
 #define CLUSTER_FLAG_NEXT_NULL 2 /* This cluster has no next cluster */
 
 /*
+ * We assign a cluster to each CPU, so each CPU can allocate swap entry from
+ * its own cluster and swapout sequentially. The purpose is to optimize swapout
+ * throughput.
+ */
+struct percpu_cluster {
+        struct swap_cluster_info index; /* Current cluster index */
+        unsigned int next; /* Likely next allocation offset */
+};
+
+/*
  * The in-memory structure used to track swap areas.
  */
 struct swap_info_struct {
@@ -217,6 +227,7 @@ struct swap_info_struct {
         unsigned int inuse_pages;       /* number of those currently in use */
         unsigned int cluster_next;      /* likely index for next allocation */
         unsigned int cluster_nr;        /* countdown to next cluster search */
+        struct percpu_cluster __percpu *percpu_cluster; /* per cpu's swap location */
         struct swap_extent *curr_swap_extent;
         struct swap_extent first_swap_extent;
         struct block_device *bdev;      /* swap device or bdev of swap file */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 98e52e373bd8..3963fc24fcc1 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -392,13 +392,78 @@ static void dec_cluster_info_page(struct swap_info_struct *p,
  * It's possible scan_swap_map() uses a free cluster in the middle of free
  * cluster list. Avoiding such abuse to avoid list corruption.
  */
-static inline bool scan_swap_map_recheck_cluster(struct swap_info_struct *si,
+static bool
+scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
         unsigned long offset)
 {
+        struct percpu_cluster *percpu_cluster;
+        bool conflict;
+
         offset /= SWAPFILE_CLUSTER;
-        return !cluster_is_null(&si->free_cluster_head) &&
+        conflict = !cluster_is_null(&si->free_cluster_head) &&
                 offset != cluster_next(&si->free_cluster_head) &&
                 cluster_is_free(&si->cluster_info[offset]);
+
+        if (!conflict)
+                return false;
+
+        percpu_cluster = this_cpu_ptr(si->percpu_cluster);
+        cluster_set_null(&percpu_cluster->index);
+        return true;
+}
+
+/*
+ * Try to get a swap entry from current cpu's swap entry pool (a cluster). This
+ * might involve allocating a new cluster for current CPU too.
+ */
+static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
+        unsigned long *offset, unsigned long *scan_base)
+{
+        struct percpu_cluster *cluster;
+        bool found_free;
+        unsigned long tmp;
+
+new_cluster:
+        cluster = this_cpu_ptr(si->percpu_cluster);
+        if (cluster_is_null(&cluster->index)) {
+                if (!cluster_is_null(&si->free_cluster_head)) {
+                        cluster->index = si->free_cluster_head;
+                        cluster->next = cluster_next(&cluster->index) *
+                                        SWAPFILE_CLUSTER;
+                } else if (!cluster_is_null(&si->discard_cluster_head)) {
+                        /*
+                         * we don't have free cluster but have some clusters in
+                         * discarding, do discard now and reclaim them
+                         */
+                        swap_do_scheduled_discard(si);
+                        *scan_base = *offset = si->cluster_next;
+                        goto new_cluster;
+                } else
+                        return;
+        }
+
+        found_free = false;
+
+        /*
+         * Other CPUs can use our cluster if they can't find a free cluster,
+         * check if there is still free entry in the cluster
+         */
+        tmp = cluster->next;
+        while (tmp < si->max && tmp < (cluster_next(&cluster->index) + 1) *
+               SWAPFILE_CLUSTER) {
+                if (!si->swap_map[tmp]) {
+                        found_free = true;
+                        break;
+                }
+                tmp++;
+        }
+        if (!found_free) {
+                cluster_set_null(&cluster->index);
+                goto new_cluster;
+        }
+        cluster->next = tmp + 1;
+        *offset = tmp;
+        *scan_base = tmp;
 }
 
 static unsigned long scan_swap_map(struct swap_info_struct *si,
@@ -423,41 +488,17 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
         si->flags += SWP_SCANNING;
         scan_base = offset = si->cluster_next;
 
+        /* SSD algorithm */
+        if (si->cluster_info) {
+                scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
+                goto checks;
+        }
+
         if (unlikely(!si->cluster_nr--)) {
                 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
                         si->cluster_nr = SWAPFILE_CLUSTER - 1;
                         goto checks;
                 }
-check_cluster:
-                if (!cluster_is_null(&si->free_cluster_head)) {
-                        offset = cluster_next(&si->free_cluster_head) *
-                                                SWAPFILE_CLUSTER;
-                        last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
-                        si->cluster_next = offset;
-                        si->cluster_nr = SWAPFILE_CLUSTER - 1;
-                        goto checks;
-                } else if (si->cluster_info) {
-                        /*
-                         * we don't have free cluster but have some clusters in
-                         * discarding, do discard now and reclaim them
-                         */
-                        if (!cluster_is_null(&si->discard_cluster_head)) {
-                                si->cluster_nr = 0;
-                                swap_do_scheduled_discard(si);
-                                scan_base = offset = si->cluster_next;
-                                if (!si->cluster_nr)
-                                        goto check_cluster;
-                                si->cluster_nr--;
-                                goto checks;
-                        }
-
-                        /*
-                         * Checking free cluster is fast enough, we can do the
-                         * check every time
-                         */
-                        si->cluster_nr = 0;
-                        goto checks;
-                }
 
                 spin_unlock(&si->lock);
 
@@ -516,8 +557,10 @@ check_cluster:
         }
 
 checks:
-        if (scan_swap_map_recheck_cluster(si, offset))
-                goto check_cluster;
+        if (si->cluster_info) {
+                while (scan_swap_map_ssd_cluster_conflict(si, offset))
+                        scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
+        }
         if (!(si->flags & SWP_WRITEOK))
                 goto no_page;
         if (!si->highest_bit)
@@ -1884,6 +1927,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
         spin_unlock(&swap_lock);
         frontswap_invalidate_area(type);
         mutex_unlock(&swapon_mutex);
+        free_percpu(p->percpu_cluster);
+        p->percpu_cluster = NULL;
         vfree(swap_map);
         vfree(cluster_info);
         vfree(frontswap_map);
@@ -2403,6 +2448,16 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
                         error = -ENOMEM;
                         goto bad_swap;
                 }
+                p->percpu_cluster = alloc_percpu(struct percpu_cluster);
+                if (!p->percpu_cluster) {
+                        error = -ENOMEM;
+                        goto bad_swap;
+                }
+                for_each_possible_cpu(i) {
+                        struct percpu_cluster *cluster;
+                        cluster = per_cpu_ptr(p->percpu_cluster, i);
+                        cluster_set_null(&cluster->index);
+                }
         }
 
         error = swap_cgroup_swapon(p->type, maxpages);
@@ -2475,6 +2530,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
         error = 0;
         goto out;
 bad_swap:
+        free_percpu(p->percpu_cluster);
+        p->percpu_cluster = NULL;
         if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
                 set_blocksize(p->bdev, p->old_block_size);
                 blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);