Re: [PATCH 04/10] mm/ksm: add identical_folio func

[David Hildenbrand]

On 04.06.24 06:24, alexs@xxxxxxxxxx wrote:
> From: "Alex Shi (tencent)" <alexs@xxxxxxxxxx>
>
> To replace pages_identical() func and further reduce the 'page' using in
> try_to_merge_one_page function.
>
> Signed-off-by: Alex Shi (tencent) <alexs@xxxxxxxxxx>
> ---
>   include/linux/mm.h | 17 +++++++++++++++++
>   mm/ksm.c           |  2 +-
>   2 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 9849dfda44d4..2d1f16ffc6ac 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4164,6 +4164,23 @@ static inline void setup_nr_node_ids(void) {}
>   
>   extern int memcmp_pages(struct page *page1, struct page *page2);
>   
> +static inline int identical_folio(struct folio *folio1, struct folio *folio2)
> +{
> +	int i, nr1, nr2, ret = 0;
> +
> +	nr1 = folio_nr_pages(folio1);
> +	nr2 = folio_nr_pages(folio2);
> +	if (nr1 != nr2)
> +		return 0;
> +
> +	for (i = 0; i < nr1; i++) {
> +		ret = memcmp_pages(folio_page(folio1, i), folio_page(folio2, i));
> +		if (ret)
> +			break;
> +	}
> +
> +	return !ret;
> +}

We never get there with large folios. So handling large folios is 
completely unnecessary.

Keep it simple: either VM_WARN_ON_ONCE when a large folio is passed, or 
simply return "false". Then, check only a single page.

--
Cheers,

David / dhildenb