Factor out the order calculation into a new helper, which can be reused
by shmem in the following patch.

Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 include/linux/pagemap.h | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index bcf0865a38ae..d796c8a33647 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -727,6 +727,16 @@ typedef unsigned int __bitwise fgf_t;
 
 #define FGP_WRITEBEGIN		(FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)
 
+static inline unsigned int filemap_get_order(size_t size)
+{
+	unsigned int shift = ilog2(size);
+
+	if (shift <= PAGE_SHIFT)
+		return 0;
+
+	return shift - PAGE_SHIFT;
+}
+
 /**
  * fgf_set_order - Encode a length in the fgf_t flags.
  * @size: The suggested size of the folio to create.
@@ -740,11 +750,11 @@ typedef unsigned int __bitwise fgf_t;
  */
 static inline fgf_t fgf_set_order(size_t size)
 {
-	unsigned int shift = ilog2(size);
+	unsigned int order = filemap_get_order(size);
 
-	if (shift <= PAGE_SHIFT)
+	if (!order)
 		return 0;
-	return (__force fgf_t)((shift - PAGE_SHIFT) << 26);
+	return (__force fgf_t)(order << 26);
 }
 
 void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
-- 
2.39.3

On 08.11.24 05:12, Baolin Wang wrote:
> Factor out the order calculation into a new helper, which can be reused
> by shmem in the following patch.
> 
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> ---
>   include/linux/pagemap.h | 16 +++++++++++++---
>   1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index bcf0865a38ae..d796c8a33647 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -727,6 +727,16 @@ typedef unsigned int __bitwise fgf_t;
>   
>   #define FGP_WRITEBEGIN		(FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)
>   
> +static inline unsigned int filemap_get_order(size_t size)
> +{
> +	unsigned int shift = ilog2(size);
> +
> +	if (shift <= PAGE_SHIFT)
> +		return 0;
> +
> +	return shift - PAGE_SHIFT;
> +}
> +

I'd have added some words somewhere, how this differs to get_order() 
[calculated order might not have space to fit the complete size] and why 
[avoid over-allocation].

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

On Fri, Nov 8, 2024 at 5:13 PM Baolin Wang
<baolin.wang@linux.alibaba.com> wrote:
>
> Factor out the order calculation into a new helper, which can be reused
> by shmem in the following patch.
>
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>

Reviewed-by: Barry Song <baohua@kernel.org>

> ---
>  include/linux/pagemap.h | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index bcf0865a38ae..d796c8a33647 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -727,6 +727,16 @@ typedef unsigned int __bitwise fgf_t;
>
>  #define FGP_WRITEBEGIN         (FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)
>
> +static inline unsigned int filemap_get_order(size_t size)
> +{
> +       unsigned int shift = ilog2(size);
> +
> +       if (shift <= PAGE_SHIFT)
> +               return 0;
> +
> +       return shift - PAGE_SHIFT;
> +}
> +
>  /**
>   * fgf_set_order - Encode a length in the fgf_t flags.
>   * @size: The suggested size of the folio to create.
> @@ -740,11 +750,11 @@ typedef unsigned int __bitwise fgf_t;
>   */
>  static inline fgf_t fgf_set_order(size_t size)
>  {
> -       unsigned int shift = ilog2(size);
> +       unsigned int order = filemap_get_order(size);
>
> -       if (shift <= PAGE_SHIFT)
> +       if (!order)
>                 return 0;
> -       return (__force fgf_t)((shift - PAGE_SHIFT) << 26);
> +       return (__force fgf_t)(order << 26);
>  }
>
>  void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
> --
> 2.39.3
>