Re: [PATCH v8 1/8] mm: Remove special swap entry functions

[Peter Xu]

On Wed, Apr 07, 2021 at 06:42:31PM +1000, Alistair Popple wrote:
> +static inline struct page *pfn_swap_entry_to_page(swp_entry_t entry)
> +{
> +	struct page *p = pfn_to_page(swp_offset(entry));
> +
> +	/*
> +	 * Any use of migration entries may only occur while the
> +	 * corresponding page is locked
> +	 */
> +	BUG_ON(is_migration_entry(entry) && !PageLocked(p));
> +
> +	return p;
> +}

Would swap_pfn_entry_to_page() be slightly better?

The thing is it's very easy to read pfn_*() as a function to take a pfn as
parameter...

Since I'm also recently working on some swap-related new ptes [1], I'm thinking
whether we could name these swap entries as "swap XXX entries".  Say, "swap
hwpoison entry", "swap pfn entry" (which is a superset of "swap migration
entry", "swap device exclusive entry", ...).  That's where I came with the
above swap_pfn_entry_to_page(), then below will be naturally is_swap_pfn_entry().

No strong opinion as this is already a v8 series (and sorry to chim in this
late), just to raise this up.

[1] https://lore.kernel.org/lkml/20210427161317.50682-1-peterx@xxxxxxxxxx/

Thanks,

> +
> +/*
> + * A pfn swap entry is a special type of swap entry that always has a pfn stored
> + * in the swap offset. They are used to represent unaddressable device memory
> + * and to restrict access to a page undergoing migration.
> + */
> +static inline bool is_pfn_swap_entry(swp_entry_t entry)
> +{
> +	return is_migration_entry(entry) || is_device_private_entry(entry);
> +}

-- 
Peter Xu