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-rw-r--r--include/linux/swap.h11
-rw-r--r--mm/swapfile.c125
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);
generated by cgit v1.2.3 (git 2.39.1) at 2024-07-05 12:49:12 +0000