Re: [PATCH v3 07/18] mm/huge_memory: move EOF trimming into the file split helper

[Kiryl Shutsemau]

On Fri, Aug 21, 2026 at 02:55:20AM +0800, Kairui Song via B4 Relay wrote:
> From: Kairui Song <kasong@xxxxxxxxxxx>
> 
> Instead of receiving @end and @nr_shmem_dropped from the caller, the
> file split helper now computes the EOF boundary and trims pages beyond
> it itself, as this is only needed for file split.  This drops the
> redundant parameter passing and sanity check.
> 
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>

Reviewed-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>

Couple of nits below.

> ---
>  mm/huge_memory.c | 42 +++++++++++++++++++-----------------------
>  1 file changed, 19 insertions(+), 23 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 69d3a6889f9e..01c8cf428595 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -4029,14 +4029,26 @@ static int __folio_freeze_split_unmapped_anon(struct folio *folio, unsigned int
>  static int __folio_freeze_split_unmapped_file(struct folio *folio, unsigned int new_order,
>  					      struct page *split_at, struct xa_state *xas,
>  					      struct address_space *mapping, bool do_lru,
> -					      struct list_head *list, enum split_type split_type,
> -					      pgoff_t end, int *nr_shmem_dropped)
> +					      struct list_head *list, enum split_type split_type)
>  {
>  	struct folio *end_folio = folio_next(folio);
>  	struct folio *new_folio, *next;
> +	int nr_shmem_dropped = 0;
>  	struct lruvec *lruvec;
> +	pgoff_t end = 0;

No need to initialize.

>  	int ret;
>  
> +	/*
> +	 * __split_frozen_folio() may need to trim off pages beyond

Does it require update?

	 * The loop below may need to trim off pages beyond

...

> +	 * EOF: but on 32-bit, i_size_read() takes an irq-unsafe
> +	 * seqlock, which cannot be nested inside the page tree lock.
> +	 * So note end now: i_size itself may be changed at any moment,
> +	 * but folio lock is good enough to serialize the trimming.
> +	 */
> +	end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
> +	if (shmem_mapping(mapping))
> +		end = shmem_fallocend(mapping->host, end);
> +
>  	xas_lock_irq(xas);
>  
>  	/*
> @@ -4101,10 +4113,9 @@ static int __folio_freeze_split_unmapped_file(struct folio *folio, unsigned int
>  			continue;
>  		}
>  
> -		VM_WARN_ON_ONCE(!nr_shmem_dropped);
>  		/* Drop folio beyond EOF: ->index >= end */
> -		if (shmem_mapping(mapping) && nr_shmem_dropped)
> -			*nr_shmem_dropped += nr_pages;
> +		if (shmem_mapping(mapping))
> +			nr_shmem_dropped += nr_pages;
>  		else if (folio_test_clear_dirty(new_folio))
>  			folio_account_cleaned(new_folio,
>  					      inode_to_wb(mapping->host));
> @@ -4125,6 +4136,8 @@ static int __folio_freeze_split_unmapped_file(struct folio *folio, unsigned int
>  
>  fail:
>  	xas_unlock_irq(xas);
> +	if (nr_shmem_dropped)
> +		shmem_uncharge(mapping->host, nr_shmem_dropped);
>  	return ret;
>  }
>  
> @@ -4161,9 +4174,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  	struct anon_vma *anon_vma = NULL;
>  	int old_order = folio_order(folio);
>  	struct folio *new_folio, *next;
> -	int nr_shmem_dropped = 0;
>  	enum ttu_flags ttu_flags = 0;
> -	pgoff_t end = 0;
>  	int ret;
>  
>  	VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
> @@ -4240,17 +4251,6 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  
>  		anon_vma = NULL;
>  		i_mmap_lock_read(mapping);
> -
> -		/*
> -		 * __split_frozen_folio() may need to trim off pages beyond
> -		 * EOF: but on 32-bit, i_size_read() takes an irq-unsafe
> -		 * seqlock, which cannot be nested inside the page tree lock.
> -		 * So note end now: i_size itself may be changed at any moment,
> -		 * but folio lock is good enough to serialize the trimming.
> -		 */
> -		end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
> -		if (shmem_mapping(mapping))
> -			end = shmem_fallocend(mapping->host, end);
>  	}
>  
>  	/*
> @@ -4266,16 +4266,12 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  
>  	if (!is_anon) {
>  		ret = __folio_freeze_split_unmapped_file(folio, new_order, split_at, &xas, mapping,
> -							 true, list, split_type, end,
> -							 &nr_shmem_dropped);
> +							 true, list, split_type);
>  	} else {
>  		ret = __folio_freeze_split_unmapped_anon(folio, new_order, split_at, true,
>  							 list, split_type);
>  	}
>  
> -	if (nr_shmem_dropped)
> -		shmem_uncharge(mapping->host, nr_shmem_dropped);
> -
>  	if (!ret && is_anon && !folio_is_device_private(folio))
>  		ttu_flags = TTU_USE_SHARED_ZEROPAGE;
>  
> 
> -- 
> 2.55.0
> 
> 

-- 
  Kiryl Shutsemau / Kirill A. Shutemov