linux-kernel - Re: [PATCH 7/7] mm, swap: simplify folio swap allocation

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Message-ID: <Z7cG636IwnSnC65d@MiWiFi-R3L-srv>
Date: Thu, 20 Feb 2025 18:41:47 +0800
From: Baoquan He <bhe@...hat.com>
To: Kairui Song <kasong@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Chris Li <chrisl@...nel.org>, Barry Song <v-songbaohua@...o.com>,
	Hugh Dickins <hughd@...gle.com>,
	Yosry Ahmed <yosryahmed@...gle.com>,
	"Huang, Ying" <ying.huang@...ux.alibaba.com>,
	Nhat Pham <nphamcs@...il.com>, Johannes Weiner <hannes@...xchg.org>,
	Kalesh Singh <kaleshsingh@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] mm, swap: simplify folio swap allocation

On 02/15/25 at 01:57am, Kairui Song wrote:
......snip..  
> -swp_entry_t folio_alloc_swap(struct folio *folio)
> +/* Rotate the device and switch to a new cluster */
> +static bool swap_alloc_rotate(swp_entry_t *entry,
> +			      unsigned char usage,
> +			      int order)

The function name is misleading which may make people thing it's a HDD
swap allocation. I would call it swap_alloc_slow() relative to the
swap_alloc_fast().

>  {
> -	unsigned int order = folio_order(folio);
> -	unsigned int size = 1 << order;
> -	struct swap_info_struct *si, *next;
> -	swp_entry_t entry = {};
> -	unsigned long offset;
>  	int node;
> +	unsigned long offset;
> +	struct swap_info_struct *si, *next;
>  
> -	if (order) {
> -		/*
> -		 * Should not even be attempting large allocations when huge
> -		 * page swap is disabled. Warn and fail the allocation.
> -		 */
> -		if (!IS_ENABLED(CONFIG_THP_SWAP) || size > SWAPFILE_CLUSTER) {
> -			VM_WARN_ON_ONCE(1);
> -			return entry;
> -		}
> -	}
> -
> -	/* Fast path using percpu cluster */
> -	local_lock(&percpu_swap_cluster.lock);
> -	if (swap_alloc_fast(&entry, SWAP_HAS_CACHE, order))
> -		goto out_alloced;
> -
> -	/* Rotate the device and switch to a new cluster */
> +	node = numa_node_id();
>  	spin_lock(&swap_avail_lock);
>  start_over:
> -	node = numa_node_id();
>  	plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
> +		/* Rotate the device and switch to a new cluster */
>  		plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
>  		spin_unlock(&swap_avail_lock);
>  		if (get_swap_device_info(si)) {
>  			offset = cluster_alloc_swap_entry(si, order, SWAP_HAS_CACHE);
>  			put_swap_device(si);
>  			if (offset) {
> -				entry = swp_entry(si->type, offset);
> -				goto out_alloced;
> +				*entry = swp_entry(si->type, offset);
> +				return true;
>  			}
>  			if (order)
> -				goto out_failed;
> +				return false;
>  		}
>  
>  		spin_lock(&swap_avail_lock);