linux-kernel - Re: [PATCH v2 11/15] mm, swap: use the swap table for the swap cache and switch API

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Message-ID: <4e0847db-0503-406b-95b4-02ee7e8f9604@redhat.com>
Date: Mon, 8 Sep 2025 15:45:11 +0200
From: David Hildenbrand <david@...hat.com>
To: Kairui Song <kasong@...cent.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>,
 Chris Li <chrisl@...nel.org>, Barry Song <baohua@...nel.org>,
 Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>,
 Kemeng Shi <shikemeng@...weicloud.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Ying Huang <ying.huang@...ux.alibaba.com>,
 Johannes Weiner <hannes@...xchg.org>, Yosry Ahmed <yosryahmed@...gle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 11/15] mm, swap: use the swap table for the swap cache
 and switch API


> +static inline struct swap_cluster_info *swap_cluster_lock(
> +	struct swap_info_struct *si, pgoff_t offset, bool irq)
> +{
> +	return NULL;
> +}
> +
> +static inline struct swap_cluster_info *swap_cluster_lock_by_folio(
> +		struct folio *folio)

I would probably call that "swap_cluster_get_and_lock" or sth like that ...

> +{
> +	return NULL;
> +}
> +
> +static inline struct swap_cluster_info *swap_cluster_lock_by_folio_irq(
> +		struct folio *folio)
> +{

... then this would become "swap_cluster_get_and_lock_irq"


Alterantively, separate the lookup from the locking of the cluster.

swap_cluster_from_folio() / folio_get_swap_cluster()
swap_cluster_lock()
swap_cluster_lock_irq()

Which might look cleaner in the end.

[...]

> -struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
> -static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
> +struct address_space swap_space __read_mostly = {
> +	.a_ops = &swap_aops,
> +};
> +
>   static bool enable_vma_readahead __read_mostly = true;
>   
>   #define SWAP_RA_ORDER_CEILING	5
> @@ -83,11 +86,21 @@ void show_swap_cache_info(void)
>    */
>   struct folio *swap_cache_get_folio(swp_entry_t entry)
>   {
> -	struct folio *folio = filemap_get_folio(swap_address_space(entry),
> -						swap_cache_index(entry));
> -	if (IS_ERR(folio))
> -		return NULL;
> -	return folio;
> +

^ superfluous empty line.

[...]

>   
> @@ -420,6 +421,34 @@ static inline unsigned int cluster_offset(struct swap_info_struct *si,
>   	return cluster_index(si, ci) * SWAPFILE_CLUSTER;
>   }
>   
> +static int swap_table_alloc_table(struct swap_cluster_info *ci)

swap_cluster_alloc_table ?

> +{
> +	WARN_ON(ci->table);
> +	ci->table = kzalloc(sizeof(unsigned long) * SWAPFILE_CLUSTER, GFP_KERNEL);
> +	if (!ci->table)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
> +static void swap_cluster_free_table(struct swap_cluster_info *ci)
> +{
> +	unsigned int ci_off;
> +	unsigned long swp_tb;
> +
> +	if (!ci->table)
> +		return;
> +
> +	for (ci_off = 0; ci_off < SWAPFILE_CLUSTER; ci_off++) {
> +		swp_tb = __swap_table_get(ci, ci_off);
> +		if (!swp_tb_is_null(swp_tb))
> +			pr_err_once("swap: unclean swap space on swapoff: 0x%lx",
> +				    swp_tb);
> +	}
> +
> +	kfree(ci->table);
> +	ci->table = NULL;
> +}
> +
>   static void move_cluster(struct swap_info_struct *si,
>   			 struct swap_cluster_info *ci, struct list_head *list,
>   			 enum swap_cluster_flags new_flags)
> @@ -702,6 +731,26 @@ static bool cluster_scan_range(struct swap_info_struct *si,
>   	return true;
>   }
>   
> +/*
> + * Currently, the swap table is not used for count tracking, just
> + * do a sanity check here to ensure nothing leaked, so the swap
> + * table should be empty upon freeing.
> + */
> +static void cluster_table_check(struct swap_cluster_info *ci,
> +				unsigned int start, unsigned int nr)

"swap_cluster_assert_table_empty()"

or sth like that that makes it clearer what you are checking for.

-- 
Cheers

David / dhildenb