From: Kairui Song <kasong@xxxxxxxxxxx>
Currently swap locking is mainly composed of two locks, cluster
lock (ci->lock) and device lock (si->lock).
Cluster lock is much more fine-grained, so it will be best to use
ci->lock instead of si->lock as much as possible.
Following the new cluster allocator design, many operation doesn't
need to touch si->lock at all. In practise, we only need to take
si->lock when moving clusters between lists.
To archive it, this commit reworked the locking pattern of all si->lock
and ci->lock users, eliminated all usage of ci->lock inside si->lock,
introduce new design to avoid touching si->lock as much as possible.
For minimal contention for allocation and easier understanding, two
ideas are introduced with the corresponding helpers: `isolation`
and `relocation`:
- Clusters will be `isolated` from list upon being scanned for
allocation, so scanning of on-list cluster no longer need to hold
the si->lock except the very moment, and hence removed the ci->lock
usage inside si->lock.
In the new allocator design, one cluster always get moved after scanning
(free -> nonfull, nonfull -> frag, frag -> frag tail) so this
introduces no extra overhead. This also greatly reduced the contention
of both si->lock and ci->lock as other CPUs won't walk onto the same
cluster by iterating the list.
The off-list time window of a cluster is also minimal, one CPU can at
most hold one cluster while scanning the 512 entries on it, which we
used to busy wait with a spin lock.
This is done with `cluster_isolate_lock` on scanning of a new cluster.
Note: Scanning of per CPU cluster is a special case, it doesn't
isolation the cluster. That's because it doesn't need to hold the
si->lock at all, it simply acquire the ci->lock of previously used
cluster and use it.
- Cluster will be `relocated` after allocation or freeing according to
it's count and status.
Allocations no longer holds si->lock now, and may drop ci->lock for
reclaim, so the cluster could be moved to anywhere. Besides,
`isolation` clears all flags when it takes the cluster off list
(The flag must be in-sync with list status, so cluster users don't
need to touch si->lock for checking its list status. This is important
for reducing contention on si->lock). So the cluster have to be
`relocated` according to its usage after being allocation to the
right list.
This is done with `relocate_cluster` after allocation, or
`[partial_]free_cluster` after freeing.
Now except swapon / swapoff and discard, `isolation` and `relocation` are
the only two places that need to take si->lock. And as each CPU will keep
using its per-CPU cluster as much as possible and a cluster have 512
entries to be consumed, si->lock is rarely touched.
The lock contention of si->lock is now barely observable. Test with build
linux kernel with defconfig showed huge performance improvement:
tiem make -j96 / 768M memcg, 4K pages, 10G ZRAM, on Intel 8255C:
Before:
Sys time: 73578.30, Real time: 864.05
After: (-50.7% sys time, -44.8% real time)
Sys time: 36227.49, Real time: 476.66
time make -j96 / 1152M memcg, 64K mTHP, 10G ZRAM, on Intel 8255C:
(avg of 4 test run)
Before:
Sys time: 74044.85, Real time: 846.51
hugepages-64kB/stats/swpout: 1735216
hugepages-64kB/stats/swpout_fallback: 430333
After: (-40.4% sys time, -37.1% real time)
Sys time: 44160.56, Real time: 532.07
hugepages-64kB/stats/swpout: 1786288
hugepages-64kB/stats/swpout_fallback: 243384
time make -j32 / 512M memcg, 4K pages, 5G ZRAM, on AMD 7K62:
Before:
Sys time: 8098.21, Real time: 401.3
After: (-22.6% sys time, -12.8% real time )
Sys time: 6265.02, Real time: 349.83
The allocation success rate also slightly improved as we sanitized the
usage of clusters with new defined helpers and locks, so temporarily
dropped si->lock or ci->lock won't cause cluster order shuffle.
Suggested-by: Chris Li <chrisl@xxxxxxxxxx>
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
include/linux/swap.h | 5 +-
mm/swapfile.c | 418 ++++++++++++++++++++++++-------------------
2 files changed, 239 insertions(+), 184 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 75fc2da1767d..a3b5d74b095a 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -265,6 +265,8 @@ enum swap_cluster_flags {
CLUSTER_FLAG_FREE,
CLUSTER_FLAG_NONFULL,
CLUSTER_FLAG_FRAG,
+ /* Clusters with flags above are allocatable */
+ CLUSTER_FLAG_USABLE = CLUSTER_FLAG_FRAG,
CLUSTER_FLAG_FULL,
CLUSTER_FLAG_DISCARD,
CLUSTER_FLAG_MAX,
@@ -290,6 +292,7 @@ enum swap_cluster_flags {
* throughput.
*/
struct percpu_cluster {
+ local_lock_t lock; /* Protect the percpu_cluster above */
unsigned int next[SWAP_NR_ORDERS]; /* Likely next allocation offset */
};
@@ -312,7 +315,7 @@ struct swap_info_struct {
/* list of cluster that contains at least one free slot */
struct list_head frag_clusters[SWAP_NR_ORDERS];
/* list of cluster that are fragmented or contented */
- unsigned int frag_cluster_nr[SWAP_NR_ORDERS];
+ atomic_long_t frag_cluster_nr[SWAP_NR_ORDERS];
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 */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 96d8012b003c..a19ee8d5ffd0 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -260,12 +260,10 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
folio_ref_sub(folio, nr_pages);
folio_set_dirty(folio);
- spin_lock(&si->lock);
/* Only sinple page folio can be backed by zswap */
if (nr_pages == 1)
zswap_invalidate(entry);
swap_entry_range_free(si, entry, nr_pages);
- spin_unlock(&si->lock);
ret = nr_pages;
out_unlock:
folio_unlock(folio);
@@ -402,7 +400,21 @@ static void discard_swap_cluster(struct swap_info_struct *si,
static inline bool cluster_is_free(struct swap_cluster_info *info)
{
- return info->flags == CLUSTER_FLAG_FREE;
+ return info->count == 0;
+}
+
+static inline bool cluster_is_discard(struct swap_cluster_info *info)
+{
+ return info->flags == CLUSTER_FLAG_DISCARD;
+}
+
+static inline bool cluster_is_usable(struct swap_cluster_info *ci, int order)
+{
+ if (unlikely(ci->flags > CLUSTER_FLAG_USABLE))
+ return false;
+ if (!order)
+ return true;
+ return cluster_is_free(ci) || order == ci->order;
}
static inline unsigned int cluster_index(struct swap_info_struct *si,
@@ -439,19 +451,20 @@ static void cluster_move(struct swap_info_struct *si,
{
VM_WARN_ON(ci->flags == new_flags);
BUILD_BUG_ON(1 << sizeof(ci->flags) * BITS_PER_BYTE < CLUSTER_FLAG_MAX);
+ lockdep_assert_held(&ci->lock);
- if (ci->flags == CLUSTER_FLAG_NONE) {
+ spin_lock(&si->lock);
+ if (ci->flags == CLUSTER_FLAG_NONE)
list_add_tail(&ci->list, list);
- } else {
- if (ci->flags == CLUSTER_FLAG_FRAG) {
- VM_WARN_ON(!si->frag_cluster_nr[ci->order]);
- si->frag_cluster_nr[ci->order]--;
- }
+ else
list_move_tail(&ci->list, list);
- }
+ spin_unlock(&si->lock);
+
+ if (ci->flags == CLUSTER_FLAG_FRAG)
+ atomic_long_dec(&si->frag_cluster_nr[ci->order]);
+ else if (new_flags == CLUSTER_FLAG_FRAG)
+ atomic_long_inc(&si->frag_cluster_nr[ci->order]);
ci->flags = new_flags;
- if (new_flags == CLUSTER_FLAG_FRAG)
- si->frag_cluster_nr[ci->order]++;
}
/* Add a cluster to discard list and schedule it to do discard */
@@ -474,39 +487,82 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si,
static void __free_cluster(struct swap_info_struct *si, struct swap_cluster_info *ci)
{
- lockdep_assert_held(&si->lock);
lockdep_assert_held(&ci->lock);
cluster_move(si, ci, &si->free_clusters, CLUSTER_FLAG_FREE);
ci->order = 0;
}
+/*
+ * Isolate and lock the first cluster that is not contented on a list,
+ * clean its flag before taken off-list. Cluster flag must be in sync
+ * with list status, so cluster updaters can always know the cluster
+ * list status without touching si lock.
+ *
+ * Note it's possible that all clusters on a list are contented so
+ * this returns NULL for an non-empty list.
+ */
+static struct swap_cluster_info *cluster_isolate_lock(
+ struct swap_info_struct *si, struct list_head *list)
+{
+ struct swap_cluster_info *ci, *ret = NULL;
+
+ spin_lock(&si->lock);
+ list_for_each_entry(ci, list, list) {
+ if (!spin_trylock(&ci->lock))
+ continue;
+
+ /* We may only isolate and clear flags of following lists */
+ VM_BUG_ON(!ci->flags);
+ VM_BUG_ON(ci->flags > CLUSTER_FLAG_USABLE &&
+ ci->flags != CLUSTER_FLAG_FULL);
+
+ list_del(&ci->list);
+ ci->flags = CLUSTER_FLAG_NONE;
+ ret = ci;
+ break;
+ }
+ spin_unlock(&si->lock);
+
+ return ret;
+}
+
/*
* Doing discard actually. After a cluster discard is finished, the cluster
- * will be added to free cluster list. caller should hold si->lock.
-*/
-static void swap_do_scheduled_discard(struct swap_info_struct *si)
+ * will be added to free cluster list. Discard cluster is a bit special as
+ * they don't participate in allocation or reclaim, so clusters marked as
+ * CLUSTER_FLAG_DISCARD must remain off-list or on discard list.
+ */
+static bool swap_do_scheduled_discard(struct swap_info_struct *si)
{
struct swap_cluster_info *ci;
+ bool ret = false;
unsigned int idx;
+ spin_lock(&si->lock);
while (!list_empty(&si->discard_clusters)) {
ci = list_first_entry(&si->discard_clusters, struct swap_cluster_info, list);
+ /*
+ * Delete the cluster from list but don't clear the flag until
+ * discard is done, so isolation and relocation will skip it.
+ */
list_del(&ci->list);
- /* Must clear flag when taking a cluster off-list */
- ci->flags = CLUSTER_FLAG_NONE;
idx = cluster_index(si, ci);
spin_unlock(&si->lock);
-
discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
SWAPFILE_CLUSTER);
- spin_lock(&si->lock);
spin_lock(&ci->lock);
- __free_cluster(si, ci);
+ /* Discard is done, return to list and clear the flag */
+ ci->flags = CLUSTER_FLAG_NONE;
memset(si->swap_map + idx * SWAPFILE_CLUSTER,
0, SWAPFILE_CLUSTER);
+ __free_cluster(si, ci);
spin_unlock(&ci->lock);
+ ret = true;
+ spin_lock(&si->lock);
}
+ spin_unlock(&si->lock);
+ return ret;
}
static void swap_discard_work(struct work_struct *work)
@@ -515,9 +571,7 @@ static void swap_discard_work(struct work_struct *work)
si = container_of(work, struct swap_info_struct, discard_work);
- spin_lock(&si->lock);
swap_do_scheduled_discard(si);
- spin_unlock(&si->lock);
}
static void swap_users_ref_free(struct percpu_ref *ref)
@@ -528,10 +582,14 @@ static void swap_users_ref_free(struct percpu_ref *ref)
complete(&si->comp);
}
+/*
+ * Must be called after freeing if ci->count == 0, puts the cluster to free
+ * or discard list.
+ */
static void free_cluster(struct swap_info_struct *si, struct swap_cluster_info *ci)
{
VM_BUG_ON(ci->count != 0);
- lockdep_assert_held(&si->lock);
+ VM_BUG_ON(ci->flags == CLUSTER_FLAG_FREE);
lockdep_assert_held(&ci->lock);
/*
@@ -548,6 +606,48 @@ static void free_cluster(struct swap_info_struct *si, struct swap_cluster_info *
__free_cluster(si, ci);
}
+/*
+ * Must be called after freeing if ci->count != 0, puts the cluster to free
+ * or nonfull list.
+ */
+static void partial_free_cluster(struct swap_info_struct *si,
+ struct swap_cluster_info *ci)
+{
+ VM_BUG_ON(!ci->count || ci->count == SWAPFILE_CLUSTER);
+ lockdep_assert_held(&ci->lock);
+
+ if (ci->flags != CLUSTER_FLAG_NONFULL)
+ cluster_move(si, ci, &si->nonfull_clusters[ci->order],
+ CLUSTER_FLAG_NONFULL);
+}
+
+/*
+ * Must be called after allocation, put the cluster to full or frag list.
+ * Note: allocation don't need si lock, and may drop the ci lock for reclaim,
+ * so the cluster could end up any where before re-acquiring ci lock.
+ */
+static void relocate_cluster(struct swap_info_struct *si,
+ struct swap_cluster_info *ci)
+{
+ lockdep_assert_held(&ci->lock);
+
+ /* Discard cluster must remain off-list or on discard list */
+ if (cluster_is_discard(ci))
+ return;
+
+ if (!ci->count) {
+ free_cluster(si, ci);
+ } else if (ci->count != SWAPFILE_CLUSTER) {
+ if (ci->flags != CLUSTER_FLAG_FRAG)
+ cluster_move(si, ci, &si->frag_clusters[ci->order],
+ CLUSTER_FLAG_FRAG);
+ } else {
+ if (ci->flags != CLUSTER_FLAG_FULL)
+ cluster_move(si, ci, &si->full_clusters,
+ CLUSTER_FLAG_FULL);
+ }
+}
+
/*
* The cluster corresponding to page_nr will be used. The cluster will not be
* added to free cluster list and its usage counter will be increased by 1.
@@ -566,30 +666,6 @@ static void inc_cluster_info_page(struct swap_info_struct *si,
VM_BUG_ON(ci->flags);
}
-/*
- * The cluster ci decreases @nr_pages usage. If the usage counter becomes 0,
- * which means no page in the cluster is in use, we can optionally discard
- * the cluster and add it to free cluster list.
- */
-static void dec_cluster_info_page(struct swap_info_struct *si,
- struct swap_cluster_info *ci, int nr_pages)
-{
- VM_BUG_ON(ci->count < nr_pages);
- VM_BUG_ON(cluster_is_free(ci));
- lockdep_assert_held(&si->lock);
- lockdep_assert_held(&ci->lock);
- ci->count -= nr_pages;
-
- if (!ci->count) {
- free_cluster(si, ci);
- return;
- }
-
- if (ci->flags != CLUSTER_FLAG_NONFULL)
- cluster_move(si, ci, &si->nonfull_clusters[ci->order],
- CLUSTER_FLAG_NONFULL);
-}
-
static bool cluster_reclaim_range(struct swap_info_struct *si,
struct swap_cluster_info *ci,
unsigned long start, unsigned long end)
@@ -599,8 +675,6 @@ static bool cluster_reclaim_range(struct swap_info_struct *si,
int nr_reclaim;
spin_unlock(&ci->lock);
- spin_unlock(&si->lock);
-
do {
switch (READ_ONCE(map[offset])) {
case 0:
@@ -618,9 +692,7 @@ static bool cluster_reclaim_range(struct swap_info_struct *si,
}
} while (offset < end);
out:
- spin_lock(&si->lock);
spin_lock(&ci->lock);
-
/*
* Recheck the range no matter reclaim succeeded or not, the slot
* could have been be freed while we are not holding the lock.
@@ -634,11 +706,11 @@ static bool cluster_reclaim_range(struct swap_info_struct *si,
static bool cluster_scan_range(struct swap_info_struct *si,
struct swap_cluster_info *ci,
- unsigned long start, unsigned int nr_pages)
+ unsigned long start, unsigned int nr_pages,
+ bool *need_reclaim)
{
unsigned long offset, end = start + nr_pages;
unsigned char *map = si->swap_map;
- bool need_reclaim = false;
for (offset = start; offset < end; offset++) {
switch (READ_ONCE(map[offset])) {
@@ -647,16 +719,13 @@ static bool cluster_scan_range(struct swap_info_struct *si,
case SWAP_HAS_CACHE:
if (!vm_swap_full())
return false;
- need_reclaim = true;
+ *need_reclaim = true;
continue;
default:
return false;
}
}
- if (need_reclaim)
- return cluster_reclaim_range(si, ci, start, end);
-
return true;
}
@@ -666,23 +735,12 @@ static void cluster_alloc_range(struct swap_info_struct *si, struct swap_cluster
{
unsigned int nr_pages = 1 << order;
- VM_BUG_ON(ci->flags != CLUSTER_FLAG_FREE &&
- ci->flags != CLUSTER_FLAG_NONFULL &&
- ci->flags != CLUSTER_FLAG_FRAG);
-
- if (cluster_is_free(ci)) {
- if (nr_pages < SWAPFILE_CLUSTER)
- cluster_move(si, ci, &si->nonfull_clusters[order],
- CLUSTER_FLAG_NONFULL);
+ if (cluster_is_free(ci))
ci->order = order;
- }
memset(si->swap_map + start, usage, nr_pages);
swap_range_alloc(si, nr_pages);
ci->count += nr_pages;
-
- if (ci->count == SWAPFILE_CLUSTER)
- cluster_move(si, ci, &si->full_clusters, CLUSTER_FLAG_FULL);
}
static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si, unsigned long offset,
@@ -692,34 +750,52 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si, unsigne
unsigned long start = offset & ~(SWAPFILE_CLUSTER - 1);
unsigned long end = min(start + SWAPFILE_CLUSTER, si->max);
unsigned int nr_pages = 1 << order;
+ bool need_reclaim, ret;
struct swap_cluster_info *ci;
- if (end < nr_pages)
- return SWAP_NEXT_INVALID;
- end -= nr_pages;
+ ci = &si->cluster_info[offset / SWAPFILE_CLUSTER];
+ lockdep_assert_held(&ci->lock);
- ci = lock_cluster(si, offset);
- if (ci->count + nr_pages > SWAPFILE_CLUSTER) {
+ if (end < nr_pages || ci->count + nr_pages > SWAPFILE_CLUSTER) {
offset = SWAP_NEXT_INVALID;
- goto done;
+ goto out;
}
- while (offset <= end) {
- if (cluster_scan_range(si, ci, offset, nr_pages)) {
- cluster_alloc_range(si, ci, offset, usage, order);
- *foundp = offset;
- if (ci->count == SWAPFILE_CLUSTER) {
+ for (end -= nr_pages; offset <= end; offset += nr_pages) {
+ need_reclaim = false;
+ if (!cluster_scan_range(si, ci, offset, nr_pages, &need_reclaim))
+ continue;
+ if (need_reclaim) {
+ ret = cluster_reclaim_range(si, ci, start, end);
+ /*
+ * Reclaim drops ci->lock and cluster could be used
+ * by another order. Not checking flag as off-list
+ * cluster has no flag set, and change of list
+ * won't cause fragmentation.
+ */
+ if (!cluster_is_usable(ci, order)) {
offset = SWAP_NEXT_INVALID;
- goto done;
+ goto out;
}
- offset += nr_pages;
- break;
+ if (cluster_is_free(ci))
+ offset = start;
+ /* Reclaim failed but cluster is usable, try next */
+ if (!ret)
+ continue;
+ }
+ cluster_alloc_range(si, ci, offset, usage, order);
+ *foundp = offset;
+ if (ci->count == SWAPFILE_CLUSTER) {
+ offset = SWAP_NEXT_INVALID;
+ goto out;
}
offset += nr_pages;
+ break;
}
if (offset > end)
offset = SWAP_NEXT_INVALID;
-done:
+out:
+ relocate_cluster(si, ci);
unlock_cluster(ci);
return offset;
}
@@ -736,18 +812,17 @@ static void swap_reclaim_full_clusters(struct swap_info_struct *si, bool force)
if (force)
to_scan = swap_usage_in_pages(si) / SWAPFILE_CLUSTER;
- while (!list_empty(&si->full_clusters)) {
- ci = list_first_entry(&si->full_clusters, struct swap_cluster_info, list);
- list_move_tail(&ci->list, &si->full_clusters);
+ while ((ci = cluster_isolate_lock(si, &si->full_clusters))) {
offset = cluster_offset(si, ci);
end = min(si->max, offset + SWAPFILE_CLUSTER);
to_scan--;
- spin_unlock(&si->lock);
while (offset < end) {
if (READ_ONCE(map[offset]) == SWAP_HAS_CACHE) {
+ spin_unlock(&ci->lock);
nr_reclaim = __try_to_reclaim_swap(si, offset,
TTRS_ANYWAY | TTRS_DIRECT);
+ spin_lock(&ci->lock);
if (nr_reclaim) {
offset += abs(nr_reclaim);
continue;
@@ -755,8 +830,8 @@ static void swap_reclaim_full_clusters(struct swap_info_struct *si, bool force)
}
offset++;
}
- spin_lock(&si->lock);
+ unlock_cluster(ci);
if (to_scan <= 0)
break;
}
@@ -768,9 +843,7 @@ static void swap_reclaim_work(struct work_struct *work)
si = container_of(work, struct swap_info_struct, reclaim_work);
- spin_lock(&si->lock);
swap_reclaim_full_clusters(si, true);
- spin_unlock(&si->lock);
}
/*
@@ -781,23 +854,36 @@ static void swap_reclaim_work(struct work_struct *work)
static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int order,
unsigned char usage)
{
- struct percpu_cluster *cluster;
struct swap_cluster_info *ci;
unsigned int offset, found = 0;
-new_cluster:
- lockdep_assert_held(&si->lock);
- cluster = this_cpu_ptr(si->percpu_cluster);
- offset = cluster->next[order];
+ /* Fast path using per CPU cluster */
+ local_lock(&si->percpu_cluster->lock);
+ offset = __this_cpu_read(si->percpu_cluster->next[order]);
if (offset) {
- offset = alloc_swap_scan_cluster(si, offset, &found, order, usage);
+ ci = lock_cluster(si, offset);
+ /* Cluster could have been used by another order */
+ if (cluster_is_usable(ci, order)) {
+ if (cluster_is_free(ci))
+ offset = cluster_offset(si, ci);
+ offset = alloc_swap_scan_cluster(si, offset, &found,
+ order, usage);
+ } else {
+ unlock_cluster(ci);
+ }
if (found)
goto done;
}
- if (!list_empty(&si->free_clusters)) {
- ci = list_first_entry(&si->free_clusters, struct swap_cluster_info, list);
- offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci), &found, order, usage);
+new_cluster:
+ ci = cluster_isolate_lock(si, &si->free_clusters);
+ if (ci) {
+ offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
+ &found, order, usage);
+ /*
+ * Allocation from free cluster must never fail and
+ * cluster lock must remain untouched.
+ */
VM_BUG_ON(!found);
goto done;
}
@@ -807,49 +893,45 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
swap_reclaim_full_clusters(si, false);
if (order < PMD_ORDER) {
- unsigned int frags = 0;
+ unsigned int frags = 0, frags_existing;
- while (!list_empty(&si->nonfull_clusters[order])) {
- ci = list_first_entry(&si->nonfull_clusters[order],
- struct swap_cluster_info, list);
- cluster_move(si, ci, &si->frag_clusters[order], CLUSTER_FLAG_FRAG);
+ while ((ci = cluster_isolate_lock(si, &si->nonfull_clusters[order]))) {
offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
&found, order, usage);
- frags++;
+ /*
+ * With `fragmenting` set to true, it will surely take
+ * the cluster off nonfull list
+ */
if (found)
goto done;
+ frags++;
}
- /*
- * Nonfull clusters are moved to frag tail if we reached
- * here, count them too, don't over scan the frag list.
- */
- while (frags < si->frag_cluster_nr[order]) {
- ci = list_first_entry(&si->frag_clusters[order],
- struct swap_cluster_info, list);
+ frags_existing = atomic_long_read(&si->frag_cluster_nr[order]);
+ while (frags < frags_existing &&
+ (ci = cluster_isolate_lock(si, &si->frag_clusters[order]))) {
+ atomic_long_dec(&si->frag_cluster_nr[order]);
/*
- * Rotate the frag list to iterate, they were all failing
- * high order allocation or moved here due to per-CPU usage,
- * this help keeping usable cluster ahead.
+ * Rotate the frag list to iterate, they were all
+ * failing high order allocation or moved here due to
+ * per-CPU usage, but either way they could contain
+ * usable (eg. lazy-freed swap cache) slots.
*/
- list_move_tail(&ci->list, &si->frag_clusters[order]);
offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
&found, order, usage);
- frags++;
if (found)
goto done;
+ frags++;
}
}
- if (!list_empty(&si->discard_clusters)) {
- /*
- * we don't have free cluster but have some clusters in
- * discarding, do discard now and reclaim them, then
- * reread cluster_next_cpu since we dropped si->lock
- */
- swap_do_scheduled_discard(si);
+ /*
+ * We don't have free cluster but have some clusters in
+ * discarding, do discard now and reclaim them, then
+ * reread cluster_next_cpu since we dropped si->lock
+ */
+ if ((si->flags & SWP_PAGE_DISCARD) && swap_do_scheduled_discard(si))
goto new_cluster;
- }
if (order)
goto done;
@@ -860,26 +942,25 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
* Clusters here have at least one usable slots and can't fail order 0
* allocation, but reclaim may drop si->lock and race with another user.
*/
- while (!list_empty(&si->frag_clusters[o])) {
- ci = list_first_entry(&si->frag_clusters[o],
- struct swap_cluster_info, list);
+ while ((ci = cluster_isolate_lock(si, &si->frag_clusters[o]))) {
+ atomic_long_dec(&si->frag_cluster_nr[o]);
offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
- &found, 0, usage);
+ &found, order, usage);
if (found)
goto done;
}
- while (!list_empty(&si->nonfull_clusters[o])) {
- ci = list_first_entry(&si->nonfull_clusters[o],
- struct swap_cluster_info, list);
+ while ((ci = cluster_isolate_lock(si, &si->nonfull_clusters[o]))) {
offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
- &found, 0, usage);
+ &found, order, usage);
if (found)
goto done;
}
}
done:
- cluster->next[order] = offset;
+ __this_cpu_write(si->percpu_cluster->next[order], offset);
+ local_unlock(&si->percpu_cluster->lock);
+
return found;
}
@@ -1135,14 +1216,11 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
spin_unlock(&swap_avail_lock);
if (get_swap_device_info(si)) {
- spin_lock(&si->lock);
n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
n_goal, swp_entries, order);
- spin_unlock(&si->lock);
put_swap_device(si);
if (n_ret || size > 1)
goto check_out;
- cond_resched();
}
spin_lock(&swap_avail_lock);
@@ -1355,9 +1433,7 @@ static bool __swap_entries_free(struct swap_info_struct *si,
if (!has_cache) {
for (i = 0; i < nr; i++)
zswap_invalidate(swp_entry(si->type, offset + i));
- spin_lock(&si->lock);
swap_entry_range_free(si, entry, nr);
- spin_unlock(&si->lock);
}
return has_cache;
@@ -1386,16 +1462,27 @@ static void swap_entry_range_free(struct swap_info_struct *si, swp_entry_t entry
unsigned char *map_end = map + nr_pages;
struct swap_cluster_info *ci;
+ /* It should never free entries across different clusters */
+ VM_BUG_ON((offset / SWAPFILE_CLUSTER) != ((offset + nr_pages - 1) / SWAPFILE_CLUSTER));
+
ci = lock_cluster(si, offset);
+ VM_BUG_ON(cluster_is_free(ci));
+ VM_BUG_ON(ci->count < nr_pages);
+
+ ci->count -= nr_pages;
do {
VM_BUG_ON(*map != SWAP_HAS_CACHE);
*map = 0;
} while (++map < map_end);
- dec_cluster_info_page(si, ci, nr_pages);
- unlock_cluster(ci);
mem_cgroup_uncharge_swap(entry, nr_pages);
swap_range_free(si, offset, nr_pages);
+
+ if (!ci->count)
+ free_cluster(si, ci);
+ else
+ partial_free_cluster(si, ci);
+ unlock_cluster(ci);
}
static void cluster_swap_free_nr(struct swap_info_struct *si,
@@ -1467,9 +1554,7 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
ci = lock_cluster(si, offset);
if (size > 1 && swap_is_has_cache(si, offset, size)) {
unlock_cluster(ci);
- spin_lock(&si->lock);
swap_entry_range_free(si, entry, size);
- spin_unlock(&si->lock);
return;
}
for (int i = 0; i < size; i++, entry.val++) {
@@ -1484,46 +1569,19 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
unlock_cluster(ci);
}
-static int swp_entry_cmp(const void *ent1, const void *ent2)
-{
- const swp_entry_t *e1 = ent1, *e2 = ent2;
-
- return (int)swp_type(*e1) - (int)swp_type(*e2);
-}
-
void swapcache_free_entries(swp_entry_t *entries, int n)
{
- struct swap_info_struct *si, *prev;
int i;
+ struct swap_info_struct *si = NULL;
if (n <= 0)
return;
- prev = NULL;
- si = NULL;
-
- /*
- * Sort swap entries by swap device, so each lock is only taken once.
- * nr_swapfiles isn't absolutely correct, but the overhead of sort() is
- * so low that it isn't necessary to optimize further.
- */
- if (nr_swapfiles > 1)
- sort(entries, n, sizeof(entries[0]), swp_entry_cmp, NULL);
for (i = 0; i < n; ++i) {
si = _swap_info_get(entries[i]);
-
- if (si != prev) {
- if (prev != NULL)
- spin_unlock(&prev->lock);
- if (si != NULL)
- spin_lock(&si->lock);
- }
if (si)
swap_entry_range_free(si, entries[i], 1);
- prev = si;
}
- if (si)
- spin_unlock(&si->lock);
}
int __swap_count(swp_entry_t entry)
@@ -1775,13 +1833,8 @@ swp_entry_t get_swap_page_of_type(int type)
goto fail;
/* This is called for allocating swap entry, not cache */
- if (get_swap_device_info(si)) {
- spin_lock(&si->lock);
- if ((si->flags & SWP_WRITEOK) && scan_swap_map_slots(si, 1, 1, &entry, 0))
- atomic_long_dec(&nr_swap_pages);
- spin_unlock(&si->lock);
- put_swap_device(si);
- }
+ if ((si->flags & SWP_WRITEOK) && scan_swap_map_slots(si, 1, 1, &entry, 0))
+ atomic_long_dec(&nr_swap_pages);
fail:
return entry;
}
@@ -3098,6 +3151,7 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
cluster = per_cpu_ptr(si->percpu_cluster, cpu);
for (i = 0; i < SWAP_NR_ORDERS; i++)
cluster->next[i] = SWAP_NEXT_INVALID;
+ local_lock_init(&cluster->lock);
}
/*
@@ -3121,7 +3175,7 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
for (i = 0; i < SWAP_NR_ORDERS; i++) {
INIT_LIST_HEAD(&si->nonfull_clusters[i]);
INIT_LIST_HEAD(&si->frag_clusters[i]);
- si->frag_cluster_nr[i] = 0;
+ atomic_long_set(&si->frag_cluster_nr[i], 0);
}
/*
@@ -3603,7 +3657,6 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
*/
goto outer;
}
- spin_lock(&si->lock);
offset = swp_offset(entry);
@@ -3668,7 +3721,6 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
spin_unlock(&si->cont_lock);
out:
unlock_cluster(ci);
- spin_unlock(&si->lock);
put_swap_device(si);
outer:
if (page)
--
2.47.0
