better shmem writeback interface for drm, was: Re: [PATCH 1/8] shmem: provide a shmem_write_folio wrapper

[Christoph Hellwig <hch@lst.de>]

Sashiko complains about a lot of pre-existing issues in i915/ttm here:

https://sashiko.dev/#/patchset/20260601113449.3464734-1-hch%40lst.de

This might be a good time to fix these, and as part of it provide
saner interfaces for drm.  The i915 case look like a plain writeback
range, which looks somewhat easy.  I don't really get what the ttm
code is trying to do.

Any takers to get drm out of messing with these lowlevel shmemfs
internals?

On Mon, Jun 01, 2026 at 01:34:27PM +0200, Christoph Hellwig wrote:
> Provide a wrapper for the shmem abuses in drm to preparare for swap I/O
> refactoring by keepin swap_iocb handling entirely contained in mm/.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 2 +-
>  drivers/gpu/drm/ttm/ttm_backup.c          | 2 +-
>  include/linux/shmem_fs.h                  | 5 +----
>  mm/shmem.c                                | 7 ++++++-
>  mm/swap.h                                 | 4 ++++
>  5 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> index 06543ae60706..ef9440166295 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> @@ -325,7 +325,7 @@ void __shmem_writeback(size_t size, struct address_space *mapping)
>  		if (folio_mapped(folio))
>  			folio_redirty_for_writepage(&wbc, folio);
>  		else
> -			error = shmem_writeout(folio, NULL, NULL);
> +			error = shmem_write_folio(folio);
>  	}
>  }
>  
> diff --git a/drivers/gpu/drm/ttm/ttm_backup.c b/drivers/gpu/drm/ttm/ttm_backup.c
> index 81df4cb5606b..c5b813a563e7 100644
> --- a/drivers/gpu/drm/ttm/ttm_backup.c
> +++ b/drivers/gpu/drm/ttm/ttm_backup.c
> @@ -117,7 +117,7 @@ ttm_backup_backup_page(struct file *backup, struct page *page,
>  	if (writeback && !folio_mapped(to_folio) &&
>  	    folio_clear_dirty_for_io(to_folio)) {
>  		folio_set_reclaim(to_folio);
> -		ret = shmem_writeout(to_folio, NULL, NULL);
> +		ret = shmem_write_folio(to_folio);
>  		if (!folio_test_writeback(to_folio))
>  			folio_clear_reclaim(to_folio);
>  		/*
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index acb8dd961b45..f35c752f27af 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -12,8 +12,6 @@
>  #include <linux/userfaultfd_k.h>
>  #include <linux/bits.h>
>  
> -struct swap_iocb;
> -
>  /* inode in-kernel data */
>  
>  #ifdef CONFIG_TMPFS_QUOTA
> @@ -122,8 +120,7 @@ static inline bool shmem_mapping(const struct address_space *mapping)
>  void shmem_unlock_mapping(struct address_space *mapping);
>  struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
>  					pgoff_t index, gfp_t gfp_mask);
> -int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
> -		struct list_head *folio_list);
> +int shmem_write_folio(struct folio *folio);
>  void shmem_truncate_range(struct inode *inode, loff_t start, uoff_t end);
>  int shmem_unuse(unsigned int type);
>  
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 56c23a7b15c7..d10735e49b25 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1738,7 +1738,12 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
>  	folio_mark_dirty(folio);
>  	return AOP_WRITEPAGE_ACTIVATE;	/* Return with folio locked */
>  }
> -EXPORT_SYMBOL_GPL(shmem_writeout);
> +
> +int shmem_write_folio(struct folio *folio)
> +{
> +	return shmem_writeout(folio, NULL, NULL);
> +}
> +EXPORT_SYMBOL_GPL(shmem_write_folio);
>  
>  #if defined(CONFIG_NUMA) && defined(CONFIG_TMPFS)
>  static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
> diff --git a/mm/swap.h b/mm/swap.h
> index 77d2d14eda42..4f86ef338a60 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -473,4 +473,8 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
>  }
>  
>  #endif /* CONFIG_SWAP */
> +
> +int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
> +		struct list_head *folio_list);
> +
>  #endif /* _MM_SWAP_H */
> -- 
> 2.53.0
> 
---end quoted text---