Re: [PATCH -next v2 2/7] mm: damon: introduce damon_get_folio()

[SeongJae Park <sj@kernel.org>]

Hi Kefeng,

Could we use 'mm/damon:' prefix instead of 'mm: damon:' for the patch subjects?

On Tue, 27 Dec 2022 20:27:09 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:

> Introduce damon_get_folio(), and the temporary wrapper function
> damon_get_page(), which help us to convert damon related function
> to use folios, and it will be droped once the conversion is completed.
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  mm/damon/ops-common.c | 14 ++++++++------
>  mm/damon/ops-common.h |  8 +++++++-
>  2 files changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
> index 75409601f934..ff38a19aa92e 100644
> --- a/mm/damon/ops-common.c
> +++ b/mm/damon/ops-common.c
> @@ -16,21 +16,23 @@
>   * Get an online page for a pfn if it's in the LRU list.  Otherwise, returns
>   * NULL.
>   *
> - * The body of this function is stolen from the 'page_idle_get_page()'.  We
> + * The body of this function is stolen from the 'page_idle_get_folio()'.  We
>   * steal rather than reuse it because the code is quite simple.
>   */
> -struct page *damon_get_page(unsigned long pfn)
> +struct folio *damon_get_folio(unsigned long pfn)
>  {
>  	struct page *page = pfn_to_online_page(pfn);
> +	struct folio *folio;
>  
>  	if (!page || !PageLRU(page) || !get_page_unless_zero(page))
>  		return NULL;
>  
> -	if (unlikely(!PageLRU(page))) {
> -		put_page(page);
> -		page = NULL;
> +	folio = page_folio(page);
> +	if (unlikely(!folio_test_lru(folio))) {
> +		folio_put(folio);
> +		folio = NULL;
>  	}

I think Matthew's comment for 'page_idle_get_folio()'[1] could applied here?


[1] https://lore.kernel.org/damon/Y6s2HPjrON2Sx%2Fgr@casper.infradead.org/

> -	return page;
> +	return folio;
>  }
>  
>  void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr)
> diff --git a/mm/damon/ops-common.h b/mm/damon/ops-common.h
> index 8d82d3722204..4ee607813981 100644
> --- a/mm/damon/ops-common.h
> +++ b/mm/damon/ops-common.h
> @@ -7,7 +7,13 @@
>  
>  #include <linux/damon.h>
>  
> -struct page *damon_get_page(unsigned long pfn);
> +struct folio *damon_get_folio(unsigned long pfn);
> +static inline struct page *damon_get_page(unsigned long pfn)
> +{
> +	struct folio *folio = damon_get_folio(pfn);
> +
> +	return &folio->page;

I think we should check if folio is NULL before dereferencing it?

> +}
>  
>  void damon_ptep_mkold(pte_t *pte, struct mm_struct *mm, unsigned long addr);
>  void damon_pmdp_mkold(pmd_t *pmd, struct mm_struct *mm, unsigned long addr);
> -- 
> 2.35.3
>