Re: [PATCH v5 01/11] mm: add PMD swap entry detection support

[Dev Jain]

[------]

> diff --git a/include/linux/leafops.h b/include/linux/leafops.h
> index 4c1476ae3234..8397193ba399 100644
> --- a/include/linux/leafops.h
> +++ b/include/linux/leafops.h
> @@ -102,6 +102,8 @@ static inline softleaf_t softleaf_from_pmd(pmd_t pmd)
>  		pmd = pmd_swp_clear_soft_dirty(pmd);
>  	if (pmd_swp_uffd(pmd))
>  		pmd = pmd_swp_clear_uffd(pmd);
> +	if (pmd_swp_exclusive(pmd))
> +		pmd = pmd_swp_clear_exclusive(pmd);
>  	arch_entry = __pmd_to_swp_entry(pmd);
>  
>  	/* Temporary until swp_entry_t eliminated. */
> @@ -634,18 +636,30 @@ static inline bool pmd_is_migration_entry(pmd_t pmd)
>   */
>  static inline bool softleaf_is_valid_pmd_entry(softleaf_t entry)
>  {
> -	/* Only device private, migration entries valid for PMD. */
> +	/* Device private, migration, and swap entries valid for PMD. */
>  	return softleaf_is_device_private(entry) ||
> -		softleaf_is_migration(entry);
> +		softleaf_is_migration(entry) ||
> +		softleaf_is_swap(entry);
> +}
> +
> +/**
> + * pmd_is_swap_entry() - Does this PMD entry encode an actual swap entry?
> + * @pmd: PMD entry.
> + *
> + * Returns: true if the PMD encodes a swap entry, otherwise false.
> + */
> +static inline bool pmd_is_swap_entry(pmd_t pmd)
> +{
> +	return softleaf_is_swap(softleaf_from_pmd(pmd));
>  }
>  
>  /**
>   * pmd_is_valid_softleaf() - Is this PMD entry a valid softleaf entry?
>   * @pmd: PMD entry.
>   *
> - * PMD leaf entries are valid only if they are device private or migration
> - * entries. This function asserts that a PMD leaf entry is valid in this
> - * respect.
> + * PMD leaf entries are valid only if they are device private, migration,
> + * or swap entries. This function asserts that a PMD leaf entry is valid
> + * in this respect.
>   *
>   * Returns: true if the PMD entry is a valid leaf entry, otherwise false.
>   */
> @@ -673,6 +687,8 @@ static inline struct folio *pmd_to_softleaf_folio(pmd_t pmd)

Nit: This function really should have been named "softleaf_pmd_to_folio", or
"pmd_softleaf_to_folio", perhaps throw in a patch to rename?


>  		VM_WARN_ON_ONCE(true);
>  		return NULL;
>  	}
> +	if (!softleaf_has_pfn(entry))
> +		return NULL;

I am guessing that after the later patches add swp support, we should
never reach pmd_to_softleaf_folio() with a swap entry, in which case,
we could add a WARN_ON_ONCE() here. (didn't check if you have done that
later, just writing this here)

>  	return softleaf_to_folio(entry);
>  }
>  
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 8c093c119e5a..e10a7e91e426 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1917,6 +1917,23 @@ static inline pmd_t pmd_swp_clear_soft_dirty(pmd_t pmd)
>  }
>  #endif
>  
> +#ifndef CONFIG_ARCH_HAS_PMD_SOFTLEAVES
> +static inline pmd_t pmd_swp_mkexclusive(pmd_t pmd)
> +{
> +	return pmd;
> +}
> +
> +static inline bool pmd_swp_exclusive(pmd_t pmd)
> +{
> +	return false;
> +}
> +
> +static inline pmd_t pmd_swp_clear_exclusive(pmd_t pmd)
> +{
> +	return pmd;
> +}
> +#endif
> +
>  #ifndef __HAVE_PFNMAP_TRACKING
>  /*
>   * Interfaces that can be used by architecture code to keep track of