Re: [PATCH] mm/huge_memory: move writeback and truncation checks early

[Zi Yan <ziy@nvidia.com>]

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On 24 Apr 2024, at 18:57, Luis Chamberlain wrote:

> We should check as early as possible if we should bail due to writeback
> or truncation. This will allow us to add further sanity checks earlier
> as well.
>
> This introduces no functional changes.
>
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
>  mm/huge_memory.c | 23 +++++++++++------------
>  1 file changed, 11 insertions(+), 12 deletions(-)
>
> While working on min order support for LBS this came up as an improvement
> as we can check for the min order early earlier, so this sets the stage
> up for that.
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 86a8c7b3b8dc..32c701821e0d 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3055,8 +3055,17 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>  	if (new_order >= folio_order(folio))
>  		return -EINVAL;
>
> -	/* Cannot split anonymous THP to order-1 */
> -	if (new_order == 1 && folio_test_anon(folio)) {
> +	if (folio_test_writeback(folio))
> +		return -EBUSY;
> +
> +	if (!folio_test_anon(folio)) {
> +		/* Truncated ? */
> +		if (!folio->mapping) {
> +			ret = -EBUSY;
> +			goto out;
> +		}
> +	} else if (new_order == 1) {
> +		/* Cannot split anonymous THP to order-1 */
>  		VM_WARN_ONCE(1, "Cannot split to order-1 folio");
>  		return -EINVAL;
>  	}
> @@ -3079,16 +3088,12 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>  		}
>  	}
>
> -
>  	is_hzp = is_huge_zero_page(&folio->page);
>  	if (is_hzp) {
>  		pr_warn_ratelimited("Called split_huge_page for huge zero page\n");
>  		return -EBUSY;
>  	}
>
> -	if (folio_test_writeback(folio))
> -		return -EBUSY;
> -
>  	if (folio_test_anon(folio)) {
>  		/*
>  		 * The caller does not necessarily hold an mmap_lock that would
> @@ -3111,12 +3116,6 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>
>  		mapping = folio->mapping;
>
> -		/* Truncated ? */
> -		if (!mapping) {
> -			ret = -EBUSY;
> -			goto out;
> -		}
> -
>  		/*
>  		 * Do not split if mapping has minimum folio order
>  		 * requirement.
> -- 
> 2.43.0
LGTM. Reviewed-by: Zi Yan <ziy@nvidia.com>

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Best Regards,
Yan, Zi

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