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

Baoquan He
2025-02-25T06:32:51Z

On 02/25/25 at 02:02am, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
>
> 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(-)

Reviewed-by: Baoquan He <bhe@redhat.com>

>
> 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
>