[PATCH v2 04/13] mm, swap: use cluster lock for HDD

Kairui Song
2024-12-24T14:39:50Z

Cluster lock (ci->lock) was introduce to reduce contention for certain
operations. Using cluster lock for HDD is not helpful as HDD have a poor
performance, so locking isn't the bottleneck. But having different set
of locks for HDD / non-HDD prevents further rework of device lock
(si->lock).

This commit just changed all lock_cluster_or_swap_info to lock_cluster,
which is a safe and straight conversion since cluster info is always
allocated now, also removed all cluster_info related checks.

Suggested-by: Chris Li <chrisl@kernel.org>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/swapfile.c | 107 ++++++++++++++++----------------------------------
1 file changed, 34 insertions(+), 73 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index fca58d43b836..d0e5b9fa0c48 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -58,10 +58,9 @@ static void swap_entry_range_free(struct swap_info_struct *si, swp_entry_t entry
static void swap_range_alloc(struct swap_info_struct *si, unsigned long offset,
unsigned int nr_entries);
static bool folio_swapcache_freeable(struct folio *folio);
-static struct swap_cluster_info *lock_cluster_or_swap_info(
- struct swap_info_struct *si, unsigned long offset);
-static void unlock_cluster_or_swap_info(struct swap_info_struct *si,
- struct swap_cluster_info *ci);
+static struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
+ unsigned long offset);
+static void unlock_cluster(struct swap_cluster_info *ci);

static DEFINE_SPINLOCK(swap_lock);
static unsigned int nr_swapfiles;
@@ -222,9 +221,9 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
* swap_map is HAS_CACHE only, which means the slots have no page table
* reference or pending writeback, and can't be allocated to others.
*/
- ci = lock_cluster_or_swap_info(si, offset);
+ ci = lock_cluster(si, offset);
need_reclaim = swap_is_has_cache(si, offset, nr_pages);
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
if (!need_reclaim)
goto out_unlock;

@@ -404,45 +403,15 @@ static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si
{
struct swap_cluster_info *ci;

- ci = si->cluster_info;
- if (ci) {
- ci += offset / SWAPFILE_CLUSTER;
- spin_lock(&ci->lock);
- }
- return ci;
-}
-
-static inline void unlock_cluster(struct swap_cluster_info *ci)
-{
- if (ci)
- spin_unlock(&ci->lock);
-}
-
-/*
- * Determine the locking method in use for this device. Return
- * swap_cluster_info if SSD-style cluster-based locking is in place.
- */
-static inline struct swap_cluster_info *lock_cluster_or_swap_info(
- struct swap_info_struct *si, unsigned long offset)
-{
- struct swap_cluster_info *ci;
-
- /* Try to use fine-grained SSD-style locking if available: */
- ci = lock_cluster(si, offset);
- /* Otherwise, fall back to traditional, coarse locking: */
- if (!ci)
- spin_lock(&si->lock);
+ ci = &si->cluster_info[offset / SWAPFILE_CLUSTER];
+ spin_lock(&ci->lock);

return ci;
}

-static inline void unlock_cluster_or_swap_info(struct swap_info_struct *si,
- struct swap_cluster_info *ci)
+static inline void unlock_cluster(struct swap_cluster_info *ci)
{
- if (ci)
- unlock_cluster(ci);
- else
- spin_unlock(&si->lock);
+ spin_unlock(&ci->lock);
}

/* Add a cluster to discard list and schedule it to do discard */
@@ -558,9 +527,6 @@ static void inc_cluster_info_page(struct swap_info_struct *si,
unsigned long idx = page_nr / SWAPFILE_CLUSTER;
struct swap_cluster_info *ci;

- if (!cluster_info)
- return;
-
ci = cluster_info + idx;
ci->count++;

@@ -576,9 +542,6 @@ static void inc_cluster_info_page(struct swap_info_struct *si,
static void dec_cluster_info_page(struct swap_info_struct *si,
struct swap_cluster_info *ci, int nr_pages)
{
- if (!si->cluster_info)
- return;
-
VM_BUG_ON(ci->count < nr_pages);
VM_BUG_ON(cluster_is_free(ci));
lockdep_assert_held(&si->lock);
@@ -1007,8 +970,6 @@ static int cluster_alloc_swap(struct swap_info_struct *si,
{
int n_ret = 0;

- VM_BUG_ON(!si->cluster_info);
-
si->flags += SWP_SCANNING;

while (n_ret < nr) {
@@ -1052,10 +1013,10 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
}

/*
- * Swapfile is not block device or not using clusters so unable
+ * Swapfile is not block device so unable
* to allocate large entries.
*/
- if (!(si->flags & SWP_BLKDEV) || !si->cluster_info)
+ if (!(si->flags & SWP_BLKDEV))
return 0;
}

@@ -1295,9 +1256,9 @@ static unsigned char __swap_entry_free(struct swap_info_struct *si,
unsigned long offset = swp_offset(entry);
unsigned char usage;

- ci = lock_cluster_or_swap_info(si, offset);
+ ci = lock_cluster(si, offset);
usage = __swap_entry_free_locked(si, offset, 1);
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
if (!usage)
free_swap_slot(entry);

@@ -1320,14 +1281,14 @@ static bool __swap_entries_free(struct swap_info_struct *si,
if (nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER)
goto fallback;

- ci = lock_cluster_or_swap_info(si, offset);
+ ci = lock_cluster(si, offset);
if (!swap_is_last_map(si, offset, nr, &has_cache)) {
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
goto fallback;
}
for (i = 0; i < nr; i++)
WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);

if (!has_cache) {
for (i = 0; i < nr; i++)
@@ -1383,7 +1344,7 @@ static void cluster_swap_free_nr(struct swap_info_struct *si,
DECLARE_BITMAP(to_free, BITS_PER_LONG) = { 0 };
int i, nr;

- ci = lock_cluster_or_swap_info(si, offset);
+ ci = lock_cluster(si, offset);
while (nr_pages) {
nr = min(BITS_PER_LONG, nr_pages);
for (i = 0; i < nr; i++) {
@@ -1391,18 +1352,18 @@ static void cluster_swap_free_nr(struct swap_info_struct *si,
bitmap_set(to_free, i, 1);
}
if (!bitmap_empty(to_free, BITS_PER_LONG)) {
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
for_each_set_bit(i, to_free, BITS_PER_LONG)
free_swap_slot(swp_entry(si->type, offset + i));
if (nr == nr_pages)
return;
bitmap_clear(to_free, 0, BITS_PER_LONG);
- ci = lock_cluster_or_swap_info(si, offset);
+ ci = lock_cluster(si, offset);
}
offset += nr;
nr_pages -= nr;
}
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
}

/*
@@ -1441,9 +1402,9 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
if (!si)
return;

- ci = lock_cluster_or_swap_info(si, offset);
+ ci = lock_cluster(si, offset);
if (size > 1 && swap_is_has_cache(si, offset, size)) {
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
spin_lock(&si->lock);
swap_entry_range_free(si, entry, size);
spin_unlock(&si->lock);
@@ -1451,14 +1412,14 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
}
for (int i = 0; i < size; i++, entry.val++) {
if (!__swap_entry_free_locked(si, offset + i, SWAP_HAS_CACHE)) {
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
free_swap_slot(entry);
if (i == size - 1)
return;
- lock_cluster_or_swap_info(si, offset);
+ lock_cluster(si, offset);
}
}
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
}

static int swp_entry_cmp(const void *ent1, const void *ent2)
@@ -1522,9 +1483,9 @@ int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
struct swap_cluster_info *ci;
int count;

- ci = lock_cluster_or_swap_info(si, offset);
+ ci = lock_cluster(si, offset);
count = swap_count(si->swap_map[offset]);
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
return count;
}

@@ -1547,7 +1508,7 @@ int swp_swapcount(swp_entry_t entry)

offset = swp_offset(entry);

- ci = lock_cluster_or_swap_info(si, offset);
+ ci = lock_cluster(si, offset);

count = swap_count(si->swap_map[offset]);
if (!(count & COUNT_CONTINUED))
@@ -1570,7 +1531,7 @@ int swp_swapcount(swp_entry_t entry)
n *= (SWAP_CONT_MAX + 1);
} while (tmp_count & COUNT_CONTINUED);
out:
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
return count;
}

@@ -1585,8 +1546,8 @@ static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
int i;
bool ret = false;

- ci = lock_cluster_or_swap_info(si, offset);
- if (!ci || nr_pages == 1) {
+ ci = lock_cluster(si, offset);
+ if (nr_pages == 1) {
if (swap_count(map[roffset]))
ret = true;
goto unlock_out;
@@ -1598,7 +1559,7 @@ static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
}
}
unlock_out:
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
return ret;
}

@@ -3428,7 +3389,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
offset = swp_offset(entry);
VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER);
VM_WARN_ON(usage == 1 && nr > 1);
- ci = lock_cluster_or_swap_info(si, offset);
+ ci = lock_cluster(si, offset);

err = 0;
for (i = 0; i < nr; i++) {
@@ -3483,7 +3444,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
}

unlock_out:
- unlock_cluster_or_swap_info(si, ci);
+ unlock_cluster(ci);
return err;
}

--
2.47.1