The quilt patch titled
Subject: mm: swap: swap cluster switch to double link list
has been removed from the -mm tree. Its filename was
mm-swap-swap-cluster-switch-to-double-link-list.patch
This patch was dropped because it had testing failures
------------------------------------------------------
From: Chris Li <chrisl@xxxxxxxxxx>
Subject: mm: swap: swap cluster switch to double link list
Date: Fri, 14 Jun 2024 16:48:07 -0700
This is the short term solutiolns "swap cluster order" listed in my "Swap
Abstraction" discussion slice 8 in the recent LSF/MM conference.
When commit 845982eb264bc ("mm: swap: allow storage of all mTHP orders")
was introduced, it only allocates the mTHP swap entries from new empty
cluster list. It has a fragmentation issue reported by Barry.
https://lore.kernel.org/all/CAGsJ_4zAcJkuW016Cfi6wicRr8N9X+GJJhgMQdSMp+Ah+NSgNQ@xxxxxxxxxxxxxx/
The mTHP allocation failure rate raises to almost 100% after a few
hours in Barry's test run.
The reason is that all the empty cluster has been exhausted while
there are planty of free swap entries to in the cluster that is
not 100% free.
Remember the swap allocation order in the cluster.
Keep track of the per order non full cluster list for later allocation.
This greatly improve the sucess rate of the mTHP swap allocation.
There is some test number in the V1 thread of this series:
https://lore.kernel.org/r/20240524-swap-allocator-v1-0-47861b423b26@xxxxxxxxxx
This patch (of 2):
Previously, the swap cluster used a cluster index as a pointer to
construct a custom single link list type "swap_cluster_list". The next
cluster pointer is shared with the cluster->count. It prevents puting the
non free cluster into a list. Change the cluster to use the standard
double link list instead. This allows tracing the nonfull cluster in the
follow up patch.
Remove the cluster getter/setter for accessing the cluster struct member.
The list operation is protected by the swap_info_struct->lock.
Change cluster code to use "struct swap_cluster_info *" to reference the
cluster rather than by using index. That is more consistent with the list
manipulation. It avoids the repeat adding index to the cluser_info. The
code is easier to understand.
Remove the cluster next pointer is NULL flag, the double link list can
handle the empty list pretty well.
The "swap_cluster_info" struct is two pointer bigger, because 512 swap
entries share one swap struct, it has very little impact on the average
memory usage per swap entry. For 1TB swapfile, the swap cluster data
structure increases from 8MB to 24MB.
Other than the list conversion, there is no real function change
in this patch.
Link: https://lkml.kernel.org/r/20240614-swap-allocator-v2-0-2a513b4a7f2f@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20240614-swap-allocator-v2-1-2a513b4a7f2f@xxxxxxxxxx
Signed-off-by: Chris Li <chrisl@xxxxxxxxxx>
Reported-by: Barry Song <21cnbao@xxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Kairui Song <kasong@xxxxxxxxxxx>
Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/swap.h | 28 +----
mm/swapfile.c | 227 ++++++++++-------------------------------
2 files changed, 70 insertions(+), 185 deletions(-)
--- a/include/linux/swap.h~mm-swap-swap-cluster-switch-to-double-link-list
+++ a/include/linux/swap.h
@@ -242,23 +242,22 @@ enum {
* space with SWAPFILE_CLUSTER pages long and naturally aligns in disk. All
* free clusters are organized into a list. We fetch an entry from the list to
* get a free cluster.
- *
- * The data field stores next cluster if the cluster is free or cluster usage
- * counter otherwise. The flags field determines if a cluster is free. This is
- * protected by swap_info_struct.lock.
*/
struct swap_cluster_info {
spinlock_t lock; /*
- * Protect swap_cluster_info fields
- * and swap_info_struct->swap_map
+ * Protect swap_cluster_info count and state
+ * field and swap_info_struct->swap_map
* elements correspond to the swap
* cluster
*/
- unsigned int data:24;
- unsigned int flags:8;
+ unsigned int count:12;
+ unsigned int state:3;
+ struct list_head list; /* Protected by swap_info_struct->lock */
};
-#define CLUSTER_FLAG_FREE 1 /* This cluster is free */
-#define CLUSTER_FLAG_NEXT_NULL 2 /* This cluster has no next cluster */
+
+#define CLUSTER_STATE_FREE 1 /* This cluster is free */
+#define CLUSTER_STATE_PER_CPU 2 /* This cluster on per_cpu_cluster */
+
/*
* The first page in the swap file is the swap header, which is always marked
@@ -283,11 +282,6 @@ struct percpu_cluster {
unsigned int next[SWAP_NR_ORDERS]; /* Likely next allocation offset */
};
-struct swap_cluster_list {
- struct swap_cluster_info head;
- struct swap_cluster_info tail;
-};
-
/*
* The in-memory structure used to track swap areas.
*/
@@ -300,7 +294,7 @@ struct swap_info_struct {
unsigned int max; /* extent of the swap_map */
unsigned char *swap_map; /* vmalloc'ed array of usage counts */
struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
- struct swap_cluster_list free_clusters; /* free clusters list */
+ struct list_head free_clusters; /* free clusters list */
unsigned int lowest_bit; /* index of first free in swap_map */
unsigned int highest_bit; /* index of last free in swap_map */
unsigned int pages; /* total of usable pages of swap */
@@ -331,7 +325,7 @@ struct swap_info_struct {
* list.
*/
struct work_struct discard_work; /* discard worker */
- struct swap_cluster_list discard_clusters; /* discard clusters list */
+ struct list_head discard_clusters; /* discard clusters list */
struct plist_node avail_lists[]; /*
* entries in swap_avail_heads, one
* entry per node.
--- a/mm/swapfile.c~mm-swap-swap-cluster-switch-to-double-link-list
+++ a/mm/swapfile.c
@@ -290,62 +290,9 @@ static void discard_swap_cluster(struct
#endif
#define LATENCY_LIMIT 256
-static inline void cluster_set_flag(struct swap_cluster_info *info,
- unsigned int flag)
-{
- info->flags = flag;
-}
-
-static inline unsigned int cluster_count(struct swap_cluster_info *info)
-{
- return info->data;
-}
-
-static inline void cluster_set_count(struct swap_cluster_info *info,
- unsigned int c)
-{
- info->data = c;
-}
-
-static inline void cluster_set_count_flag(struct swap_cluster_info *info,
- unsigned int c, unsigned int f)
-{
- info->flags = f;
- info->data = c;
-}
-
-static inline unsigned int cluster_next(struct swap_cluster_info *info)
-{
- return info->data;
-}
-
-static inline void cluster_set_next(struct swap_cluster_info *info,
- unsigned int n)
-{
- info->data = n;
-}
-
-static inline void cluster_set_next_flag(struct swap_cluster_info *info,
- unsigned int n, unsigned int f)
-{
- info->flags = f;
- info->data = n;
-}
-
static inline bool cluster_is_free(struct swap_cluster_info *info)
{
- return info->flags & CLUSTER_FLAG_FREE;
-}
-
-static inline bool cluster_is_null(struct swap_cluster_info *info)
-{
- return info->flags & CLUSTER_FLAG_NEXT_NULL;
-}
-
-static inline void cluster_set_null(struct swap_cluster_info *info)
-{
- info->flags = CLUSTER_FLAG_NEXT_NULL;
- info->data = 0;
+ return info->state == CLUSTER_STATE_FREE;
}
static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
@@ -394,65 +341,11 @@ static inline void unlock_cluster_or_swa
spin_unlock(&si->lock);
}
-static inline bool cluster_list_empty(struct swap_cluster_list *list)
-{
- return cluster_is_null(&list->head);
-}
-
-static inline unsigned int cluster_list_first(struct swap_cluster_list *list)
-{
- return cluster_next(&list->head);
-}
-
-static void cluster_list_init(struct swap_cluster_list *list)
-{
- cluster_set_null(&list->head);
- cluster_set_null(&list->tail);
-}
-
-static void cluster_list_add_tail(struct swap_cluster_list *list,
- struct swap_cluster_info *ci,
- unsigned int idx)
-{
- if (cluster_list_empty(list)) {
- cluster_set_next_flag(&list->head, idx, 0);
- cluster_set_next_flag(&list->tail, idx, 0);
- } else {
- struct swap_cluster_info *ci_tail;
- unsigned int tail = cluster_next(&list->tail);
-
- /*
- * Nested cluster lock, but both cluster locks are
- * only acquired when we held swap_info_struct->lock
- */
- ci_tail = ci + tail;
- spin_lock_nested(&ci_tail->lock, SINGLE_DEPTH_NESTING);
- cluster_set_next(ci_tail, idx);
- spin_unlock(&ci_tail->lock);
- cluster_set_next_flag(&list->tail, idx, 0);
- }
-}
-
-static unsigned int cluster_list_del_first(struct swap_cluster_list *list,
- struct swap_cluster_info *ci)
-{
- unsigned int idx;
-
- idx = cluster_next(&list->head);
- if (cluster_next(&list->tail) == idx) {
- cluster_set_null(&list->head);
- cluster_set_null(&list->tail);
- } else
- cluster_set_next_flag(&list->head,
- cluster_next(&ci[idx]), 0);
-
- return idx;
-}
-
/* Add a cluster to discard list and schedule it to do discard */
static void swap_cluster_schedule_discard(struct swap_info_struct *si,
- unsigned int idx)
+ struct swap_cluster_info *ci)
{
+ unsigned int idx = ci - si->cluster_info;
/*
* If scan_swap_map_slots() can't find a free cluster, it will check
* si->swap_map directly. To make sure the discarding cluster isn't
@@ -462,17 +355,14 @@ static void swap_cluster_schedule_discar
memset(si->swap_map + idx * SWAPFILE_CLUSTER,
SWAP_MAP_BAD, SWAPFILE_CLUSTER);
- cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx);
-
+ list_add_tail(&ci->list, &si->discard_clusters);
schedule_work(&si->discard_work);
}
-static void __free_cluster(struct swap_info_struct *si, unsigned long idx)
+static void __free_cluster(struct swap_info_struct *si, struct swap_cluster_info *ci)
{
- struct swap_cluster_info *ci = si->cluster_info;
-
- cluster_set_flag(ci + idx, CLUSTER_FLAG_FREE);
- cluster_list_add_tail(&si->free_clusters, ci, idx);
+ ci->state = CLUSTER_STATE_FREE;
+ list_add_tail(&ci->list, &si->free_clusters);
}
/*
@@ -481,21 +371,22 @@ static void __free_cluster(struct swap_i
*/
static void swap_do_scheduled_discard(struct swap_info_struct *si)
{
- struct swap_cluster_info *info, *ci;
+ struct swap_cluster_info *ci;
unsigned int idx;
- info = si->cluster_info;
-
- while (!cluster_list_empty(&si->discard_clusters)) {
- idx = cluster_list_del_first(&si->discard_clusters, info);
+ while (!list_empty(&si->discard_clusters)) {
+ ci = list_first_entry(&si->discard_clusters, struct swap_cluster_info, list);
+ list_del(&ci->list);
+ idx = ci - si->cluster_info;
spin_unlock(&si->lock);
discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
SWAPFILE_CLUSTER);
spin_lock(&si->lock);
- ci = lock_cluster(si, idx * SWAPFILE_CLUSTER);
- __free_cluster(si, idx);
+
+ spin_lock(&ci->lock);
+ __free_cluster(si, ci);
memset(si->swap_map + idx * SWAPFILE_CLUSTER,
0, SWAPFILE_CLUSTER);
unlock_cluster(ci);
@@ -521,20 +412,19 @@ static void swap_users_ref_free(struct p
complete(&si->comp);
}
-static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
+static struct swap_cluster_info *alloc_cluster(struct swap_info_struct *si, unsigned long idx)
{
- struct swap_cluster_info *ci = si->cluster_info;
+ struct swap_cluster_info *ci = list_first_entry(&si->free_clusters, struct swap_cluster_info, list);
- VM_BUG_ON(cluster_list_first(&si->free_clusters) != idx);
- cluster_list_del_first(&si->free_clusters, ci);
- cluster_set_count_flag(ci + idx, 0, 0);
+ VM_BUG_ON(ci - si->cluster_info != idx);
+ list_del(&ci->list);
+ ci->count = 0;
+ return ci;
}
-static void free_cluster(struct swap_info_struct *si, unsigned long idx)
+static void free_cluster(struct swap_info_struct *si, struct swap_cluster_info *ci)
{
- struct swap_cluster_info *ci = si->cluster_info + idx;
-
- VM_BUG_ON(cluster_count(ci) != 0);
+ VM_BUG_ON(ci->count != 0);
/*
* If the swap is discardable, prepare discard the cluster
* instead of free it immediately. The cluster will be freed
@@ -542,11 +432,11 @@ static void free_cluster(struct swap_inf
*/
if ((si->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
(SWP_WRITEOK | SWP_PAGE_DISCARD)) {
- swap_cluster_schedule_discard(si, idx);
+ swap_cluster_schedule_discard(si, ci);
return;
}
- __free_cluster(si, idx);
+ __free_cluster(si, ci);
}
/*
@@ -559,15 +449,15 @@ static void add_cluster_info_page(struct
unsigned long count)
{
unsigned long idx = page_nr / SWAPFILE_CLUSTER;
+ struct swap_cluster_info *ci = cluster_info + idx;
if (!cluster_info)
return;
- if (cluster_is_free(&cluster_info[idx]))
+ if (cluster_is_free(ci))
alloc_cluster(p, idx);
- VM_BUG_ON(cluster_count(&cluster_info[idx]) + count > SWAPFILE_CLUSTER);
- cluster_set_count(&cluster_info[idx],
- cluster_count(&cluster_info[idx]) + count);
+ VM_BUG_ON(ci->count + count > SWAPFILE_CLUSTER);
+ ci->count += count;
}
/*
@@ -581,24 +471,20 @@ static void inc_cluster_info_page(struct
}
/*
- * The cluster corresponding to page_nr decreases one usage. If the usage
- * counter becomes 0, which means no page in the cluster is in using, we can
- * optionally discard the cluster and add it to free cluster list.
+ * The cluster ci decreases one usage. If the usage counter becomes 0,
+ * which means no page in the cluster is in using, we can optionally discard
+ * the cluster and add it to free cluster list.
*/
-static void dec_cluster_info_page(struct swap_info_struct *p,
- struct swap_cluster_info *cluster_info, unsigned long page_nr)
+static void dec_cluster_info_page(struct swap_info_struct *p, struct swap_cluster_info *ci)
{
- unsigned long idx = page_nr / SWAPFILE_CLUSTER;
-
- if (!cluster_info)
+ if (!p->cluster_info)
return;
- VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
- cluster_set_count(&cluster_info[idx],
- cluster_count(&cluster_info[idx]) - 1);
+ VM_BUG_ON(ci->count == 0);
+ ci->count--;
- if (cluster_count(&cluster_info[idx]) == 0)
- free_cluster(p, idx);
+ if (!ci->count)
+ free_cluster(p, ci);
}
/*
@@ -611,10 +497,10 @@ scan_swap_map_ssd_cluster_conflict(struc
{
struct percpu_cluster *percpu_cluster;
bool conflict;
-
+ struct swap_cluster_info *first = list_first_entry(&si->free_clusters, struct swap_cluster_info, list);
offset /= SWAPFILE_CLUSTER;
- conflict = !cluster_list_empty(&si->free_clusters) &&
- offset != cluster_list_first(&si->free_clusters) &&
+ conflict = !list_empty(&si->free_clusters) &&
+ offset != first - si->cluster_info &&
cluster_is_free(&si->cluster_info[offset]);
if (!conflict)
@@ -655,10 +541,14 @@ new_cluster:
cluster = this_cpu_ptr(si->percpu_cluster);
tmp = cluster->next[order];
if (tmp == SWAP_NEXT_INVALID) {
- if (!cluster_list_empty(&si->free_clusters)) {
- tmp = cluster_next(&si->free_clusters.head) *
- SWAPFILE_CLUSTER;
- } else if (!cluster_list_empty(&si->discard_clusters)) {
+ if (!list_empty(&si->free_clusters)) {
+ ci = list_first_entry(&si->free_clusters, struct swap_cluster_info, list);
+ list_del(&ci->list);
+ spin_lock(&ci->lock);
+ ci->state = CLUSTER_STATE_PER_CPU;
+ spin_unlock(&ci->lock);
+ tmp = (ci - si->cluster_info) * SWAPFILE_CLUSTER;
+ } else 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
@@ -1062,8 +952,8 @@ static void swap_free_cluster(struct swa
ci = lock_cluster(si, offset);
memset(si->swap_map + offset, 0, SWAPFILE_CLUSTER);
- cluster_set_count_flag(ci, 0, 0);
- free_cluster(si, idx);
+ ci->count = 0;
+ free_cluster(si, ci);
unlock_cluster(ci);
swap_range_free(si, offset, SWAPFILE_CLUSTER);
}
@@ -1336,7 +1226,7 @@ static void swap_entry_free(struct swap_
count = p->swap_map[offset];
VM_BUG_ON(count != SWAP_HAS_CACHE);
p->swap_map[offset] = 0;
- dec_cluster_info_page(p, p->cluster_info, offset);
+ dec_cluster_info_page(p, ci);
unlock_cluster(ci);
mem_cgroup_uncharge_swap(entry, 1);
@@ -3003,8 +2893,8 @@ static int setup_swap_map_and_extents(st
nr_good_pages = maxpages - 1; /* omit header page */
- cluster_list_init(&p->free_clusters);
- cluster_list_init(&p->discard_clusters);
+ INIT_LIST_HEAD(&p->free_clusters);
+ INIT_LIST_HEAD(&p->discard_clusters);
for (i = 0; i < swap_header->info.nr_badpages; i++) {
unsigned int page_nr = swap_header->info.badpages[i];
@@ -3055,14 +2945,15 @@ static int setup_swap_map_and_extents(st
for (k = 0; k < SWAP_CLUSTER_COLS; k++) {
j = (k + col) % SWAP_CLUSTER_COLS;
for (i = 0; i < DIV_ROUND_UP(nr_clusters, SWAP_CLUSTER_COLS); i++) {
+ struct swap_cluster_info *ci;
idx = i * SWAP_CLUSTER_COLS + j;
+ ci = cluster_info + idx;
if (idx >= nr_clusters)
continue;
- if (cluster_count(&cluster_info[idx]))
+ if (ci->count)
continue;
- cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
- cluster_list_add_tail(&p->free_clusters, cluster_info,
- idx);
+ ci->state = CLUSTER_STATE_FREE;
+ list_add_tail(&ci->list, &p->free_clusters);
}
}
return nr_extents;
_
Patches currently in -mm which might be from chrisl@xxxxxxxxxx are
mm-swap-mthp-allocate-swap-entries-from-nonfull-list.patch
