Re: [PATCH 1/3] mm: move offset_in_page() to page_helpers.h

[Lorenzo Stoakes <ljs@kernel.org>]

Seriously, please resend this.

This is 3 patches with 2 in-reply-to 1/3, that's not how we do series in mm,
take a look around :)

Write a cover letter, and have all the patches in-reply-to that.

Was there not previous versions of this? I _seem_ to remember that, but might be
misremembering :)

Also I'm really questioning the value of this, you've not sold why we should
take this whatsoever.

'Add a random new header file we have to maintain because it's smaller' is not
really hugely compelling.

Also a _lot_ of stuff in the kernel ultimately pulls in mm.h. So what exactly
has the specific requirement of both needing this define and (somehow) doesn't
use mm?

On Sun, May 17, 2026 at 02:34:29PM +0200, Thorsten Blum wrote:
> Move offset_in_page() out of linux/mm.h so users that only need page
> offset calculations can include this lightweight header instead of
> pulling in all of linux/mm.h.

What's the motivation? What caused you to want to do this? Why should we have a
new tiny header with only this define? What makes that important?

Why is pulling in a 'big' header file such an issue?

This commit message is pretty useless right now, you're just saying what you're
doing, yeah I can see that from the diff.

You should use the commit message to explain why and what for etc.

>
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
>  include/linux/mm.h           |  2 +-
>  include/linux/page_helpers.h | 10 ++++++++++

You've added a new file and not updated MAINTAINERS, nor indicated that it will
be caught by a glob?

Also super super restrictive to have 'page helpers', that's likely to be tiny
forever, why not just move this macro to mm_types.h and import that instead?
It's highly likely it's already imported wherever you need it, anyway.

>  2 files changed, 11 insertions(+), 1 deletion(-)
>  create mode 100644 include/linux/page_helpers.h
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index af23453e9dbd..bf49e52f749a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -17,6 +17,7 @@
>  #include <linux/mm_types.h>
>  #include <linux/mmap_lock.h>
>  #include <linux/range.h>
> +#include <linux/page_helpers.h>
>  #include <linux/pfn.h>
>  #include <linux/percpu-refcount.h>
>  #include <linux/bit_spinlock.h>
> @@ -3033,7 +3034,6 @@ static inline void clear_page_pfmemalloc(struct page *page)
>   */
>  extern void pagefault_out_of_memory(void);
>
> -#define offset_in_page(p)	((unsigned long)(p) & ~PAGE_MASK)
>  #define offset_in_folio(folio, p) ((unsigned long)(p) & (folio_size(folio) - 1))
>
>  /*
> diff --git a/include/linux/page_helpers.h b/include/linux/page_helpers.h
> new file mode 100644
> index 000000000000..102a4f3c3868
> --- /dev/null
> +++ b/include/linux/page_helpers.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0 */

No description of what this is for?

> +
> +#ifndef _LINUX_PAGE_HELPERS_H
> +#define _LINUX_PAGE_HELPERS_H
> +
> +#include <asm/page.h>
> +
> +#define offset_in_page(p)	((unsigned long)(p) & ~PAGE_MASK)

Why are you only porting the page version when ostensibly folios are more likely
to be the unit-of-operation in future?

> +
> +#endif /* _LINUX_PAGE_HELPERS_H */

Thanks, Lorenzo