[PATCH v2 4/7] mm, swap: don't update the counter up-front

Kairui Song
2025-02-24T18:03:06Z

The counter update before allocation design was useful to avoid
unnecessary scan when device is full, so it will abort early if the
counter indicates the device is full. But that is an uncommon case,
and now scanning of a full device is very fast, so the up-front update
is not helpful any more.

Remove it and simplify the slot allocation logic.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/swapfile.c | 18 ++----------------
1 file changed, 2 insertions(+), 16 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6f2de59c6355..db836670c334 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1201,22 +1201,10 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
int order = swap_entry_order(entry_order);
unsigned long size = 1 << order;
struct swap_info_struct *si, *next;
- long avail_pgs;
int n_ret = 0;
int node;

spin_lock(&swap_avail_lock);
-
- avail_pgs = atomic_long_read(&nr_swap_pages) / size;
- if (avail_pgs <= 0) {
- spin_unlock(&swap_avail_lock);
- goto noswap;
- }
-
- n_goal = min3((long)n_goal, (long)SWAP_BATCH, avail_pgs);
-
- atomic_long_sub(n_goal * size, &nr_swap_pages);
-
start_over:
node = numa_node_id();
plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
@@ -1250,10 +1238,8 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
spin_unlock(&swap_avail_lock);

check_out:
- if (n_ret < n_goal)
- atomic_long_add((long)(n_goal - n_ret) * size,
- &nr_swap_pages);
-noswap:
+ atomic_long_sub(n_ret * size, &nr_swap_pages);
+
return n_ret;
}

--
2.48.1