Commit bae8a4ef authored by Kairui Song's avatar Kairui Song Committed by Andrew Morton
Browse files

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: default avatarKairui Song <kasong@tencent.com>
Suggested-by: default avatarChris 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 3f641cf9

include/linux/swap.h

+2 −0
Original line number Diff line number Diff line
@@ -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 */

mm/swapfile.c

+40 −14
Original line number Diff line number Diff line
@@ -820,7 +820,10 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si, 
out:

	relocate_cluster(si, ci);

	unlock_cluster(ci);

	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;



	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 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o 
		}

	}

done:

	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);
@@ -3189,6 +3203,7 @@ 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);



	if (si->flags & SWP_SOLIDSTATE) {

		si->percpu_cluster = alloc_percpu(struct percpu_cluster);

		if (!si->percpu_cluster)

			goto err_free;
@@ -3201,6 +3216,15 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si, 
				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++)

			si->global_cluster->next[i] = SWAP_ENTRY_INVALID;

		spin_lock_init(&si->global_cluster_lock);

	}



	/*

	 * Mark unusable pages as unavailable. The clusters aren't
@@ -3473,6 +3497,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) 
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);