Re: [PATCH v5 11/17] mm/huge_memory: move filemap management into the file split helper

[Yeoreum Yun <yeoreum.yun@arm.com>]

Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>

On Tue, Sep 15, 2026 at 01:14:52AM +0800, Kairui Song via B4 Relay wrote:
> From: Kairui Song <kasong@tencent.com>
> 
> Only file split needs the filemap and xarray handling and related
> variables.  Move them out of __folio_split() into the file helper so
> the helper is self-contained, and simplify the parameters.
> 
> No functional change.
> 
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> Signed-off-by: Kairui Song <kasong@tencent.com>
> ---
>  mm/huge_memory.c | 102 ++++++++++++++++++++++++-------------------------------
>  1 file changed, 44 insertions(+), 58 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 859aefda7356..8fc1dd5b8354 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -4107,16 +4107,42 @@ static int __folio_freeze_split_anon(struct folio *folio,
>  
>  static int __folio_freeze_split_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)
>  {
> +	struct address_space *mapping = folio->mapping;
> +	XA_STATE(xas, &mapping->i_pages, folio->index);
>  	struct folio *end_folio = folio_next(folio);
>  	struct folio *new_folio, *next;
>  	int nr_shmem_dropped = 0;
> +	unsigned int min_order;
>  	struct lruvec *lruvec;
>  	pgoff_t end;
> -	int ret;
> +	gfp_t gfp;
> +	int ret = 0;
> +
> +	min_order = mapping_min_folio_order(mapping);
> +	if (new_order < min_order)
> +		return -EINVAL;
> +
> +	gfp = current_gfp_context(mapping_gfp_mask(mapping) & GFP_RECLAIM_MASK);
> +	if (!filemap_release_folio(folio, gfp))
> +		return -EBUSY;
> +
> +	mapping_set_update(&xas, mapping);
> +
> +	if (split_type == SPLIT_TYPE_UNIFORM) {
> +		int old_order = folio_order(folio);
> +
> +		xas_set_order(&xas, folio->index, new_order);
> +		xas_split_alloc(&xas, folio, old_order, gfp);
> +		if (xas_error(&xas)) {
> +			ret = xas_error(&xas);
> +			goto fail_free;
> +		}
> +	}
> +
> +	i_mmap_lock_read(mapping);
>  
>  	/* Currently device private folios can only back anonymous memory. */
>  	VM_WARN_ON_ONCE_FOLIO(folio_is_device_private(folio), folio);
> @@ -4134,15 +4160,15 @@ static int __folio_freeze_split_file(struct folio *folio,
>  
>  	ret = unmap_folio(folio);
>  	if (ret)
> -		return ret;
> +		goto fail_mmap_unlock;
>  
> -	xas_lock_irq(xas);
> +	xas_lock_irq(&xas);
>  
>  	/*
>  	 * Check if the folio is present in page cache.
>  	 * We assume all tail are present too, if folio is there.
>  	 */
> -	if (xas_load(xas) != folio) {
> +	if (xas_load(&xas) != folio) {
>  		ret = -EAGAIN;
>  		goto fail;
>  	}
> @@ -4169,7 +4195,7 @@ static int __folio_freeze_split_file(struct folio *folio,
>  	if (do_lru)
>  		lruvec = folio_lruvec_lock(folio);
>  
> -	ret = __split_frozen_folio(folio, new_order, split_at, xas,
> +	ret = __split_frozen_folio(folio, new_order, split_at, &xas,
>  				   mapping, split_type);
>  
>  	/*
> @@ -4225,9 +4251,19 @@ static int __folio_freeze_split_file(struct folio *folio,
>  	 * If we want to use try_to_migrate() on file in unmap_folio,
>  	 * remember to add remap_anon_folio() and adapt it.
>  	 */
> -	xas_unlock_irq(xas);
> +	xas_unlock_irq(&xas);
> +fail_mmap_unlock:
>  	if (nr_shmem_dropped)
>  		shmem_uncharge(mapping->host, nr_shmem_dropped);
> +	/*
> +	 * Drop the mapping while the inode is still pinned. @folio stays
> +	 * locked and present in the page cache, so eviction cannot free
> +	 * the inode yet, nothing past this point may touch the inode or
> +	 * the mapping.
> +	 */
> +	i_mmap_unlock_read(mapping);
> +fail_free:
> +	xas_destroy(&xas);
>  	return ret;
>  }
>  
> @@ -4256,11 +4292,9 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  		struct page *split_at, struct page *lock_at,
>  		struct list_head *list, enum split_type split_type)
>  {
> -	XA_STATE(xas, &folio->mapping->i_pages, folio->index);
>  	struct folio *end_folio = folio_next(folio);
>  	bool is_anon = folio_test_anon(folio);
>  	struct mem_cgroup *memcg, *old_memcg;
> -	struct address_space *mapping = NULL;
>  	struct anon_vma *anon_vma = NULL;
>  	int old_order = folio_order(folio);
>  	struct folio *new_folio, *next;
> @@ -4307,60 +4341,15 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  			goto out;
>  		}
>  		anon_vma_lock_write(anon_vma);
> -		mapping = NULL;
> -	} else {
> -		unsigned int min_order;
> -		gfp_t gfp;
> -
> -		mapping = folio->mapping;
> -		min_order = mapping_min_folio_order(mapping);
> -		if (new_order < min_order) {
> -			ret = -EINVAL;
> -			goto out;
> -		}
> -
> -		gfp = current_gfp_context(mapping_gfp_mask(mapping) &
> -							GFP_RECLAIM_MASK);
> -
> -		if (!filemap_release_folio(folio, gfp)) {
> -			ret = -EBUSY;
> -			goto out;
> -		}
> -
> -		mapping_set_update(&xas, mapping);
> -
> -		if (split_type == SPLIT_TYPE_UNIFORM) {
> -			xas_set_order(&xas, folio->index, new_order);
> -			xas_split_alloc(&xas, folio, old_order, gfp);
> -			if (xas_error(&xas)) {
> -				ret = xas_error(&xas);
> -				goto out;
> -			}
> -		}
> -
> -		anon_vma = NULL;
> -		i_mmap_lock_read(mapping);
>  	}
>  
>  	if (is_anon)
>  		ret = __folio_freeze_split_anon(folio, new_order, split_at,
>  						true, list, split_type);
>  	else
> -		ret = __folio_freeze_split_file(folio, new_order, split_at, &xas, mapping,
> +		ret = __folio_freeze_split_file(folio, new_order, split_at,
>  						true, list, split_type);
>  
> -	/*
> -	 * Drop the mapping while the inode is still pinned. @folio stays
> -	 * locked and present in the page cache until the loop below, so
> -	 * eviction cannot free the inode yet; @lock_at is not enough, it may
> -	 * be a tail beyond EOF that the split already dropped from the page
> -	 * cache. Nothing past this point may touch the inode or the mapping.
> -	 */
> -	if (mapping) {
> -		i_mmap_unlock_read(mapping);
> -		mapping = NULL;
> -	}
> -
>  	/*
>  	 * Unlock all after-split folios except the one containing
>  	 * @lock_at page. If @folio is not split, it will be kept locked.
> @@ -4384,14 +4373,11 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
>  		anon_vma_unlock_write(anon_vma);
>  		put_anon_vma(anon_vma);
>  	}
> -	if (mapping)
> -		i_mmap_unlock_read(mapping);
>  out:
>  	/* restore to caller's old_memcg */
>  	set_active_memcg(old_memcg);
>  	mem_cgroup_put(memcg);
>  out_no_memcg:
> -	xas_destroy(&xas);
>  	if (is_pmd_order(old_order))
>  		count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
>  	count_mthp_stat(old_order, !ret ? MTHP_STAT_SPLIT : MTHP_STAT_SPLIT_FAILED);
> 
> -- 
> 2.55.0
> 
> 

-- 
Sincerely,
Yeoreum Yun