mm, swap: don't update the counter up-front

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.

Link: https://lkml.kernel.org/r/20250224180212.22802-5-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6f2de59c6355e60952b94787a0559349a21ac2f3..db836670c334217154115e8fe120d0fa73bbce3f 100644 (file)
--- 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 @@ start_over:
        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;
 }