The patch titled
Subject: mm, swap: use an enum to define all cluster flags and wrap flags changes
has been added to the -mm mm-unstable branch. Its filename is
mm-swap-use-an-enum-to-define-all-cluster-flags-and-wrap-flags-changes.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-use-an-enum-to-define-all-cluster-flags-and-wrap-flags-changes.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Kairui Song <kasong@xxxxxxxxxxx>
Subject: mm, swap: use an enum to define all cluster flags and wrap flags changes
Date: Tue, 14 Jan 2025 01:57:27 +0800
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 many bits. Additionally, the current mixed
usage of '&' and '==' is a bit confusing.
Make it clean by using an enum to define all possible cluster statuses.
Only an off-list cluster will have the NONE (0) flag. And use a wrapper
to annotate and sanitize all flag settings and list movements.
Link: https://lkml.kernel.org/r/20250113175732.48099-9-ryncsn@xxxxxxxxx
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
Suggested-by: Chris Li <chrisl@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Barry Song <v-songbaohua@xxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxxxxxxxxxx>
Cc: Hugh Dickens <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/swap.h | 17 +++++++--
mm/swapfile.c | 76 +++++++++++++++++++++--------------------
2 files changed, 53 insertions(+), 40 deletions(-)
--- a/include/linux/swap.h~mm-swap-use-an-enum-to-define-all-cluster-flags-and-wrap-flags-changes
+++ a/include/linux/swap.h
@@ -257,10 +257,19 @@ 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,
+ /* Clusters with flags above are allocatable */
+ CLUSTER_FLAG_USABLE = 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
--- a/mm/swapfile.c~mm-swap-use-an-enum-to-define-all-cluster-flags-and-wrap-flags-changes
+++ a/mm/swapfile.c
@@ -403,7 +403,7 @@ static void discard_swap_cluster(struct
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,
@@ -434,6 +434,28 @@ static inline void unlock_cluster(struct
spin_unlock(&ci->lock);
}
+static void move_cluster(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)
@@ -447,10 +469,8 @@ static void swap_cluster_schedule_discar
*/
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);
+ move_cluster(si, ci, &si->discard_clusters, CLUSTER_FLAG_DISCARD);
schedule_work(&si->discard_work);
}
@@ -458,12 +478,7 @@ static void __free_cluster(struct swap_i
{
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;
+ move_cluster(si, ci, &si->free_clusters, CLUSTER_FLAG_FREE);
ci->order = 0;
}
@@ -479,6 +494,8 @@ static void swap_do_scheduled_discard(st
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);
@@ -519,9 +536,6 @@ static void free_cluster(struct swap_inf
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
@@ -573,13 +587,9 @@ static void dec_cluster_info_page(struct
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)
+ move_cluster(si, ci, &si->nonfull_clusters[ci->order],
+ CLUSTER_FLAG_NONFULL);
}
static bool cluster_reclaim_range(struct swap_info_struct *si,
@@ -663,11 +673,13 @@ static bool cluster_alloc_range(struct s
if (!(si->flags & SWP_WRITEOK))
return false;
+ VM_BUG_ON(ci->flags == CLUSTER_FLAG_NONE);
+ VM_BUG_ON(ci->flags > CLUSTER_FLAG_USABLE);
+
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)
+ move_cluster(si, ci, &si->nonfull_clusters[order],
+ CLUSTER_FLAG_NONFULL);
ci->order = order;
}
@@ -675,14 +687,8 @@ static bool cluster_alloc_range(struct s
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)
+ move_cluster(si, ci, &si->full_clusters, CLUSTER_FLAG_FULL);
return true;
}
@@ -821,9 +827,7 @@ new_cluster:
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]++;
+ move_cluster(si, ci, &si->frag_clusters[order], CLUSTER_FLAG_FRAG);
offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
&found, order, usage);
frags++;
_
Patches currently in -mm which might be from kasong@xxxxxxxxxxx are
mm-memcontrol-avoid-duplicated-memcg-enable-check.patch
mm-swap_cgroup-remove-swap_cgroup_cmpxchg.patch
mm-swap_cgroup-remove-global-swap-cgroup-lock.patch
mm-swap_cgroup-decouple-swap-cgroup-recording-and-clearing.patch
mm-swap-minor-clean-up-for-swap-entry-allocation.patch
mm-swap-fold-swap_info_get_cont-in-the-only-caller.patch
mm-swap-remove-old-allocation-path-for-hdd.patch
mm-swap-use-cluster-lock-for-hdd.patch
mm-swap-clean-up-device-availability-check.patch
mm-swap-clean-up-plist-removal-and-adding.patch
mm-swap-hold-a-reference-during-scan-and-cleanup-flag-usage.patch
mm-swap-use-an-enum-to-define-all-cluster-flags-and-wrap-flags-changes.patch
mm-swap-reduce-contention-on-device-lock.patch
mm-swap-simplify-percpu-cluster-updating.patch
mm-swap-introduce-a-helper-for-retrieving-cluster-from-offset.patch
mm-swap-use-a-global-swap-cluster-for-non-rotation-devices.patch
mm-swap_slots-remove-slot-cache-for-freeing-path.patch
