Re: [PATCH 01/12] swap: remove the maxpages variable in sys_swapon

[Damien Le Moal <dlemoal@kernel.org>]

On 5/12/26 14:35, Christoph Hellwig wrote:
> Always use si->max which is updated setup_swap_extents instead of copying
> into and out of maxpages.

Checking mm/swapfile.c, I see s->max being set only in swapon(). Is this a typo
or am I misunderstanding this sentence ?

Looks good otherwise, but it would be nice to rename ->max to ->maxpages to make
it clear what this is counting.

> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  mm/swapfile.c | 27 +++++++++++----------------
>  1 file changed, 11 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 9174f1eeffb0..f7ebd97e28a3 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3350,10 +3350,9 @@ static unsigned long read_swap_header(struct swap_info_struct *si,
>  }
>  
>  static int setup_swap_clusters_info(struct swap_info_struct *si,
> -				    union swap_header *swap_header,
> -				    unsigned long maxpages)
> +				    union swap_header *swap_header)
>  {
> -	unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
> +	unsigned long nr_clusters = DIV_ROUND_UP(si->max, SWAPFILE_CLUSTER);
>  	struct swap_cluster_info *cluster_info;
>  	int err = -ENOMEM;
>  	unsigned long i;
> @@ -3395,7 +3394,7 @@ static int setup_swap_clusters_info(struct swap_info_struct *si,
>  		if (err)
>  			goto err;
>  	}
> -	for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++) {
> +	for (i = si->max; i < round_up(si->max, SWAPFILE_CLUSTER); i++) {
>  		err = swap_cluster_setup_bad_slot(si, cluster_info, i, true);
>  		if (err)
>  			goto err;
> @@ -3425,7 +3424,7 @@ static int setup_swap_clusters_info(struct swap_info_struct *si,
>  	si->cluster_info = cluster_info;
>  	return 0;
>  err:
> -	free_swap_cluster_info(cluster_info, maxpages);
> +	free_swap_cluster_info(cluster_info, si->max);
>  	return err;
>  }
>  
> @@ -3440,7 +3439,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  	union swap_header *swap_header;
>  	int nr_extents;
>  	sector_t span;
> -	unsigned long maxpages;
>  	struct folio *folio = NULL;
>  	struct inode *inode = NULL;
>  	bool inced_nr_rotate_swap = false;
> @@ -3512,14 +3510,13 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  	}
>  	swap_header = kmap_local_folio(folio, 0);
>  
> -	maxpages = read_swap_header(si, swap_header, inode);
> -	if (unlikely(!maxpages)) {
> +	si->max = read_swap_header(si, swap_header, inode);
> +	if (unlikely(!si->max)) {
>  		error = -EINVAL;
>  		goto bad_swap_unlock_inode;
>  	}
>  
> -	si->max = maxpages;
> -	si->pages = maxpages - 1;
> +	si->pages = si->max - 1;
>  	nr_extents = setup_swap_extents(si, swap_file, &span);
>  	if (nr_extents < 0) {
>  		error = nr_extents;
> @@ -3531,14 +3528,12 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  		goto bad_swap_unlock_inode;
>  	}
>  
> -	maxpages = si->max;
> -
>  	/* Set up the swap cluster info */
> -	error = setup_swap_clusters_info(si, swap_header, maxpages);
> +	error = setup_swap_clusters_info(si, swap_header);
>  	if (error)
>  		goto bad_swap_unlock_inode;
>  
> -	error = swap_cgroup_swapon(si->type, maxpages);
> +	error = swap_cgroup_swapon(si->type, si->max);
>  	if (error)
>  		goto bad_swap_unlock_inode;
>  
> @@ -3546,7 +3541,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  	 * Use kvmalloc_array instead of bitmap_zalloc as the allocation order might
>  	 * be above MAX_PAGE_ORDER incase of a large swap file.
>  	 */
> -	si->zeromap = kvmalloc_array(BITS_TO_LONGS(maxpages), sizeof(long),
> +	si->zeromap = kvmalloc_array(BITS_TO_LONGS(si->max), sizeof(long),
>  				     GFP_KERNEL | __GFP_ZERO);
>  	if (!si->zeromap) {
>  		error = -ENOMEM;
> @@ -3597,7 +3592,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  		}
>  	}
>  
> -	error = zswap_swapon(si->type, maxpages);
> +	error = zswap_swapon(si->type, si->max);
>  	if (error)
>  		goto bad_swap_unlock_inode;
>  


-- 
Damien Le Moal
Western Digital Research