mm, swap: use a global swap cluster for non-rotation devices

Non-rotational devices (SSD / ZRAM) can tolerate fragmentation, so the
goal of the SWAP allocator is to avoid contention for clusters.  It uses a
per-CPU cluster design, and each CPU will use a different cluster as much
as possible.

However, HDDs are very sensitive to fragmentation, contention is trivial
in comparison.  Therefore, we use one global cluster instead.  This
ensures that each order will be written to the same cluster as much as
possible, which helps make the I/O more continuous.

This ensures that the performance of the cluster allocator is as good as
that of the old allocator.  Tests after this commit compared to those
before this series:

Tested using 'make -j32' with tinyconfig, a 1G memcg limit, and HDD swap:

make -j32 with tinyconfig, using 1G memcg limit and HDD swap:

Before this series:
114.44user 29.11system 39:42.90elapsed 6%CPU (0avgtext+0avgdata 157284maxresident)k
2901232inputs+0outputs (238877major+4227640minor)pagefaults

After this commit:
113.90user 23.81system 38:11.77elapsed 6%CPU (0avgtext+0avgdata 157260maxresident)k
2548728inputs+0outputs (235471major+4238110minor)pagefaults

[ryncsn@gmail.com: check kmalloc() return in setup_clusters]
Link: https://lkml.kernel.org/r/CAMgjq7Au+o04ckHyT=iU-wVx9az=t0B-ZiC5E0bDqNrAtNOP-g@mail.gmail.com
Link: https://lkml.kernel.org/r/20250113175732.48099-13-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Suggested-by: Chris Li <chrisl@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickens <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 75b2b0166cb107a34660f66635b2d4f6a606e79a..a5f475335aea8742f5ab6274c813486161120f6d 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -317,6 +317,8 @@ struct swap_info_struct {
        unsigned int pages;             /* total of usable pages of swap */
        atomic_long_t inuse_pages;      /* number of those currently in use */
        struct percpu_cluster __percpu *percpu_cluster; /* per cpu's swap location */
+       struct percpu_cluster *global_cluster; /* Use one global cluster for rotating device */
+       spinlock_t global_cluster_lock; /* Serialize usage of global cluster */
        struct rb_root swap_extent_root;/* root of the swap extent rbtree */
        struct block_device *bdev;      /* swap device or bdev of swap file */
        struct file *swap_file;         /* seldom referenced */

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 37d540fa03101a82658e0314998c9e0cf9e9ac54..adf97c9ccb96ddd6a7861d96c3139db6f1b48ce8 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -820,7 +820,10 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si,
 out:
        relocate_cluster(si, ci);
        unlock_cluster(ci);
-       __this_cpu_write(si->percpu_cluster->next[order], next);
+       if (si->flags & SWP_SOLIDSTATE)
+               __this_cpu_write(si->percpu_cluster->next[order], next);
+       else
+               si->global_cluster->next[order] = next;
        return found;
 }
 
@@ -881,9 +884,16 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
        struct swap_cluster_info *ci;
        unsigned int offset, found = 0;
 
-       /* Fast path using per CPU cluster */
-       local_lock(&si->percpu_cluster->lock);
-       offset = __this_cpu_read(si->percpu_cluster->next[order]);
+       if (si->flags & SWP_SOLIDSTATE) {
+               /* Fast path using per CPU cluster */
+               local_lock(&si->percpu_cluster->lock);
+               offset = __this_cpu_read(si->percpu_cluster->next[order]);
+       } else {
+               /* Serialize HDD SWAP allocation for each device. */
+               spin_lock(&si->global_cluster_lock);
+               offset = si->global_cluster->next[order];
+       }
+
        if (offset) {
                ci = lock_cluster(si, offset);
                /* Cluster could have been used by another order */
@@ -975,8 +985,10 @@ new_cluster:
                }
        }
 done:
-       local_unlock(&si->percpu_cluster->lock);
-
+       if (si->flags & SWP_SOLIDSTATE)
+               local_unlock(&si->percpu_cluster->lock);
+       else
+               spin_unlock(&si->global_cluster_lock);
        return found;
 }
 
@@ -2784,6 +2796,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
        mutex_unlock(&swapon_mutex);
        free_percpu(p->percpu_cluster);
        p->percpu_cluster = NULL;
+       kfree(p->global_cluster);
+       p->global_cluster = NULL;
        vfree(swap_map);
        kvfree(zeromap);
        kvfree(cluster_info);
@@ -3189,17 +3203,27 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
        for (i = 0; i < nr_clusters; i++)
                spin_lock_init(&cluster_info[i].lock);
 
-       si->percpu_cluster = alloc_percpu(struct percpu_cluster);
-       if (!si->percpu_cluster)
-               goto err_free;
+       if (si->flags & SWP_SOLIDSTATE) {
+               si->percpu_cluster = alloc_percpu(struct percpu_cluster);
+               if (!si->percpu_cluster)
+                       goto err_free;
 
-       for_each_possible_cpu(cpu) {
-               struct percpu_cluster *cluster;
+               for_each_possible_cpu(cpu) {
+                       struct percpu_cluster *cluster;
 
-               cluster = per_cpu_ptr(si->percpu_cluster, cpu);
+                       cluster = per_cpu_ptr(si->percpu_cluster, cpu);
+                       for (i = 0; i < SWAP_NR_ORDERS; i++)
+                               cluster->next[i] = SWAP_ENTRY_INVALID;
+                       local_lock_init(&cluster->lock);
+               }
+       } else {
+               si->global_cluster = kmalloc(sizeof(*si->global_cluster),
+                                    GFP_KERNEL);
+               if (!si->global_cluster)
+                       goto err_free;
                for (i = 0; i < SWAP_NR_ORDERS; i++)
-                       cluster->next[i] = SWAP_ENTRY_INVALID;
-               local_lock_init(&cluster->lock);
+                       si->global_cluster->next[i] = SWAP_ENTRY_INVALID;
+               spin_lock_init(&si->global_cluster_lock);
        }
 
        /*
@@ -3473,6 +3497,8 @@ bad_swap_unlock_inode:
 bad_swap:
        free_percpu(si->percpu_cluster);
        si->percpu_cluster = NULL;
+       kfree(si->global_cluster);
+       si->global_cluster = NULL;
        inode = NULL;
        destroy_swap_extents(si);
        swap_cgroup_swapoff(si->type);