From: Kairui Song <kasong@xxxxxxxxxxx>
Currently we are only using flags to indicate which list the cluster is
on, using one bit for each list type might be a waste as the list type
grows we will consume too much bits. And current the mixed usage of "&"
and "==" is a bit confusing.
Make it clean by using an enum to define all possible cluster status,
only an off-list cluster will have the NONE (0) flag. And use
a wrapper to annotate and sanitize all flag setting and list movement.
Suggested-by: Chris Li <chrisl@xxxxxxxxxx>
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
include/linux/swap.h | 17 +++++++---
mm/swapfile.c | 76 +++++++++++++++++++++++---------------------
2 files changed, 53 insertions(+), 40 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 1651174959c8..75fc2da1767d 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -256,10 +256,19 @@ struct swap_cluster_info {
u8 order;
struct list_head list;
};
-#define CLUSTER_FLAG_FREE 1 /* This cluster is free */
-#define CLUSTER_FLAG_NONFULL 2 /* This cluster is on nonfull list */
-#define CLUSTER_FLAG_FRAG 4 /* This cluster is on nonfull list */
-#define CLUSTER_FLAG_FULL 8 /* This cluster is on full list */
+
+/*
+ * All on-list cluster must have a non-zero flag.
+ */
+enum swap_cluster_flags {
+ CLUSTER_FLAG_NONE = 0, /* For temporary off-list cluster */
+ CLUSTER_FLAG_FREE,
+ CLUSTER_FLAG_NONFULL,
+ CLUSTER_FLAG_FRAG,
+ CLUSTER_FLAG_FULL,
+ CLUSTER_FLAG_DISCARD,
+ CLUSTER_FLAG_MAX,
+};
/*
* The first page in the swap file is the swap header, which is always marked
diff --git a/mm/swapfile.c b/mm/swapfile.c
index d6b6e71ccc19..96d8012b003c 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -402,7 +402,7 @@ 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->flags == CLUSTER_FLAG_FREE;
}
static inline unsigned int cluster_index(struct swap_info_struct *si,
@@ -433,6 +433,27 @@ static inline void unlock_cluster(struct swap_cluster_info *ci)
spin_unlock(&ci->lock);
}
+static void cluster_move(struct swap_info_struct *si,
+ struct swap_cluster_info *ci, struct list_head *list,
+ enum swap_cluster_flags new_flags)
+{
+ VM_WARN_ON(ci->flags == new_flags);
+ BUILD_BUG_ON(1 << sizeof(ci->flags) * BITS_PER_BYTE < CLUSTER_FLAG_MAX);
+
+ 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]--;
+ }
+ list_move_tail(&ci->list, list);
+ }
+ 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 */
static void swap_cluster_schedule_discard(struct swap_info_struct *si,
struct swap_cluster_info *ci)
@@ -446,10 +467,8 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si,
*/
memset(si->swap_map + idx * SWAPFILE_CLUSTER,
SWAP_MAP_BAD, SWAPFILE_CLUSTER);
-
- VM_BUG_ON(ci->flags & CLUSTER_FLAG_FREE);
- list_move_tail(&ci->list, &si->discard_clusters);
- ci->flags = 0;
+ VM_BUG_ON(ci->flags == CLUSTER_FLAG_FREE);
+ cluster_move(si, ci, &si->discard_clusters, CLUSTER_FLAG_DISCARD);
schedule_work(&si->discard_work);
}
@@ -457,12 +476,7 @@ static void __free_cluster(struct swap_info_struct *si, struct swap_cluster_info
{
lockdep_assert_held(&si->lock);
lockdep_assert_held(&ci->lock);
-
- if (ci->flags)
- list_move_tail(&ci->list, &si->free_clusters);
- else
- list_add_tail(&ci->list, &si->free_clusters);
- ci->flags = CLUSTER_FLAG_FREE;
+ cluster_move(si, ci, &si->free_clusters, CLUSTER_FLAG_FREE);
ci->order = 0;
}
@@ -478,6 +492,8 @@ static void swap_do_scheduled_discard(struct swap_info_struct *si)
while (!list_empty(&si->discard_clusters)) {
ci = list_first_entry(&si->discard_clusters, struct swap_cluster_info, list);
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);
@@ -518,9 +534,6 @@ static void free_cluster(struct swap_info_struct *si, struct swap_cluster_info *
lockdep_assert_held(&si->lock);
lockdep_assert_held(&ci->lock);
- if (ci->flags & CLUSTER_FLAG_FRAG)
- si->frag_cluster_nr[ci->order]--;
-
/*
* If the swap is discardable, prepare discard the cluster
* instead of free it immediately. The cluster will be freed
@@ -572,13 +585,9 @@ static void dec_cluster_info_page(struct swap_info_struct *si,
return;
}
- if (!(ci->flags & CLUSTER_FLAG_NONFULL)) {
- VM_BUG_ON(ci->flags & CLUSTER_FLAG_FREE);
- if (ci->flags & CLUSTER_FLAG_FRAG)
- si->frag_cluster_nr[ci->order]--;
- list_move_tail(&ci->list, &si->nonfull_clusters[ci->order]);
- ci->flags = CLUSTER_FLAG_NONFULL;
- }
+ 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,
@@ -657,11 +666,14 @@ 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) {
- list_move_tail(&ci->list, &si->nonfull_clusters[order]);
- ci->flags = CLUSTER_FLAG_NONFULL;
- }
+ if (nr_pages < SWAPFILE_CLUSTER)
+ cluster_move(si, ci, &si->nonfull_clusters[order],
+ CLUSTER_FLAG_NONFULL);
ci->order = order;
}
@@ -669,14 +681,8 @@ static void cluster_alloc_range(struct swap_info_struct *si, struct swap_cluster
swap_range_alloc(si, nr_pages);
ci->count += nr_pages;
- if (ci->count == SWAPFILE_CLUSTER) {
- VM_BUG_ON(!(ci->flags &
- (CLUSTER_FLAG_FREE | CLUSTER_FLAG_NONFULL | CLUSTER_FLAG_FRAG)));
- if (ci->flags & CLUSTER_FLAG_FRAG)
- si->frag_cluster_nr[ci->order]--;
- list_move_tail(&ci->list, &si->full_clusters);
- ci->flags = CLUSTER_FLAG_FULL;
- }
+ 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,
@@ -806,9 +812,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
while (!list_empty(&si->nonfull_clusters[order])) {
ci = list_first_entry(&si->nonfull_clusters[order],
struct swap_cluster_info, list);
- list_move_tail(&ci->list, &si->frag_clusters[order]);
- ci->flags = CLUSTER_FLAG_FRAG;
- si->frag_cluster_nr[order]++;
+ cluster_move(si, ci, &si->frag_clusters[order], CLUSTER_FLAG_FRAG);
offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
&found, order, usage);
frags++;
--
2.47.0
