Re: [PATCH 11/12] shmem: add file length arg in shmem_get_folio() path

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, May 15, 2024 at 05:57:36AM +0000, Daniel Gomez wrote:
> In preparation for large folio in the write and fallocate paths, add
> file length argument in shmem_get_folio() path to be able to calculate
> the folio order based on the file size. Use of order-0 (PAGE_SIZE) for
> read, page cache read, and vm fault.
> 
> This enables high order folios in the write and fallocate path once the
> folio order is calculated based on the length.
> 
> Signed-off-by: Daniel Gomez <da.gomez@samsung.com>
> ---
>  fs/xfs/scrub/xfile.c     |  6 +++---
>  fs/xfs/xfs_buf_mem.c     |  3 ++-
>  include/linux/shmem_fs.h |  2 +-
>  mm/khugepaged.c          |  3 ++-
>  mm/shmem.c               | 35 ++++++++++++++++++++---------------
>  mm/userfaultfd.c         |  2 +-
>  6 files changed, 29 insertions(+), 22 deletions(-)
> 
> diff --git a/fs/xfs/scrub/xfile.c b/fs/xfs/scrub/xfile.c
> index 8cdd863db585..4905f5e4cb5d 100644
> --- a/fs/xfs/scrub/xfile.c
> +++ b/fs/xfs/scrub/xfile.c
> @@ -127,7 +127,7 @@ xfile_load(
>  		unsigned int	offset;
>  
>  		if (shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> -				SGP_READ) < 0)
> +				SGP_READ, PAGE_SIZE) < 0)

I suppose I /did/ say during LSFMM that for the current users of xfile.c
and xfs_buf_mem.c the order of the folio being returned doesn't really
matter, but why wouldn't the last argument here be "roundup_64(count,
PAGE_SIZE)" ?  Shouldn't we at least hint to the page cache about the
folio order that we actually want instead of limiting it to order-0?

(Also it seems a little odd to me that the @index is in units of pgoff_t
but @len is in bytes.)

>  			break;
>  		if (!folio) {
>  			/*
> @@ -197,7 +197,7 @@ xfile_store(
>  		unsigned int	offset;
>  
>  		if (shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> -				SGP_CACHE) < 0)
> +				SGP_CACHE, PAGE_SIZE) < 0)
>  			break;
>  		if (filemap_check_wb_err(inode->i_mapping, 0)) {
>  			folio_unlock(folio);
> @@ -268,7 +268,7 @@ xfile_get_folio(
>  
>  	pflags = memalloc_nofs_save();
>  	error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> -			(flags & XFILE_ALLOC) ? SGP_CACHE : SGP_READ);
> +			(flags & XFILE_ALLOC) ? SGP_CACHE : SGP_READ, PAGE_SIZE);
>  	memalloc_nofs_restore(pflags);
>  	if (error)
>  		return ERR_PTR(error);
> diff --git a/fs/xfs/xfs_buf_mem.c b/fs/xfs/xfs_buf_mem.c
> index 9bb2d24de709..784c81d35a1f 100644
> --- a/fs/xfs/xfs_buf_mem.c
> +++ b/fs/xfs/xfs_buf_mem.c
> @@ -149,7 +149,8 @@ xmbuf_map_page(
>  		return -ENOMEM;
>  	}
>  
> -	error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio, SGP_CACHE);
> +	error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio, SGP_CACHE,
> +				PAGE_SIZE);

This is ok unless someone wants to use a different XMBUF_BLOCKSIZE.

--D

>  	if (error)
>  		return error;
>  
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index 3fb18f7eb73e..bc59b4a00228 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -142,7 +142,7 @@ enum sgp_type {
>  };
>  
>  int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
> -		enum sgp_type sgp);
> +		enum sgp_type sgp, size_t len);
>  struct folio *shmem_read_folio_gfp(struct address_space *mapping,
>  		pgoff_t index, gfp_t gfp);
>  
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 38830174608f..947770ded68c 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1863,7 +1863,8 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
>  				xas_unlock_irq(&xas);
>  				/* swap in or instantiate fallocated page */
>  				if (shmem_get_folio(mapping->host, index,
> -						&folio, SGP_NOALLOC)) {
> +						    &folio, SGP_NOALLOC,
> +						    PAGE_SIZE)) {
>  					result = SCAN_FAIL;
>  					goto xa_unlocked;
>  				}
> diff --git a/mm/shmem.c b/mm/shmem.c
> index d531018ffece..fcd2c9befe19 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1134,7 +1134,7 @@ static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index)
>  	 * (although in some cases this is just a waste of time).
>  	 */
>  	folio = NULL;
> -	shmem_get_folio(inode, index, &folio, SGP_READ);
> +	shmem_get_folio(inode, index, &folio, SGP_READ, PAGE_SIZE);
>  	return folio;
>  }
>  
> @@ -1844,7 +1844,7 @@ static struct folio *shmem_alloc_folio(gfp_t gfp, struct shmem_inode_info *info,
>  
>  static struct folio *shmem_alloc_and_add_folio(gfp_t gfp,
>  		struct inode *inode, pgoff_t index,
> -		struct mm_struct *fault_mm, bool huge)
> +		struct mm_struct *fault_mm, bool huge, size_t len)
>  {
>  	struct address_space *mapping = inode->i_mapping;
>  	struct shmem_inode_info *info = SHMEM_I(inode);
> @@ -2173,7 +2173,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
>   */
>  static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
>  		struct folio **foliop, enum sgp_type sgp, gfp_t gfp,
> -		struct vm_fault *vmf, vm_fault_t *fault_type)
> +		struct vm_fault *vmf, vm_fault_t *fault_type, size_t len)
>  {
>  	struct vm_area_struct *vma = vmf ? vmf->vma : NULL;
>  	struct mm_struct *fault_mm;
> @@ -2258,7 +2258,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
>  		huge_gfp = vma_thp_gfp_mask(vma);
>  		huge_gfp = limit_gfp_mask(huge_gfp, gfp);
>  		folio = shmem_alloc_and_add_folio(huge_gfp,
> -				inode, index, fault_mm, true);
> +				inode, index, fault_mm, true, len);
>  		if (!IS_ERR(folio)) {
>  			count_vm_event(THP_FILE_ALLOC);
>  			goto alloced;
> @@ -2267,7 +2267,8 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
>  			goto repeat;
>  	}
>  
> -	folio = shmem_alloc_and_add_folio(gfp, inode, index, fault_mm, false);
> +	folio = shmem_alloc_and_add_folio(gfp, inode, index, fault_mm, false,
> +					  len);
>  	if (IS_ERR(folio)) {
>  		error = PTR_ERR(folio);
>  		if (error == -EEXIST)
> @@ -2377,10 +2378,10 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
>   * Return: 0 if successful, else a negative error code.
>   */
>  int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
> -		enum sgp_type sgp)
> +		enum sgp_type sgp, size_t len)
>  {
>  	return shmem_get_folio_gfp(inode, index, foliop, sgp,
> -			mapping_gfp_mask(inode->i_mapping), NULL, NULL);
> +			mapping_gfp_mask(inode->i_mapping), NULL, NULL, len);
>  }
>  EXPORT_SYMBOL_GPL(shmem_get_folio);
>  
> @@ -2475,7 +2476,7 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
>  
>  	WARN_ON_ONCE(vmf->page != NULL);
>  	err = shmem_get_folio_gfp(inode, vmf->pgoff, &folio, SGP_CACHE,
> -				  gfp, vmf, &ret);
> +				  gfp, vmf, &ret, PAGE_SIZE);
>  	if (err)
>  		return vmf_error(err);
>  	if (folio) {
> @@ -2954,6 +2955,9 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
>  	struct folio *folio;
>  	int ret = 0;
>  
> +	if (!mapping_large_folio_support(mapping))
> +		len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos));
> +
>  	/* i_rwsem is held by caller */
>  	if (unlikely(info->seals & (F_SEAL_GROW |
>  				   F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))) {
> @@ -2963,7 +2967,7 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
>  			return -EPERM;
>  	}
>  
> -	ret = shmem_get_folio(inode, index, &folio, SGP_WRITE);
> +	ret = shmem_get_folio(inode, index, &folio, SGP_WRITE, len);
>  	if (ret)
>  		return ret;
>  
> @@ -3083,7 +3087,7 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
>  				break;
>  		}
>  
> -		error = shmem_get_folio(inode, index, &folio, SGP_READ);
> +		error = shmem_get_folio(inode, index, &folio, SGP_READ, PAGE_SIZE);
>  		if (error) {
>  			if (error == -EINVAL)
>  				error = 0;
> @@ -3260,7 +3264,7 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
>  			break;
>  
>  		error = shmem_get_folio(inode, *ppos / PAGE_SIZE, &folio,
> -					SGP_READ);
> +					SGP_READ, PAGE_SIZE);
>  		if (error) {
>  			if (error == -EINVAL)
>  				error = 0;
> @@ -3469,7 +3473,8 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
>  			error = -ENOMEM;
>  		else
>  			error = shmem_get_folio(inode, index, &folio,
> -						SGP_FALLOC);
> +						SGP_FALLOC,
> +						(end - index) << PAGE_SHIFT);
>  		if (error) {
>  			info->fallocend = undo_fallocend;
>  			/* Remove the !uptodate folios we added */
> @@ -3822,7 +3827,7 @@ static int shmem_symlink(struct mnt_idmap *idmap, struct inode *dir,
>  	} else {
>  		inode_nohighmem(inode);
>  		inode->i_mapping->a_ops = &shmem_aops;
> -		error = shmem_get_folio(inode, 0, &folio, SGP_WRITE);
> +		error = shmem_get_folio(inode, 0, &folio, SGP_WRITE, PAGE_SIZE);
>  		if (error)
>  			goto out_remove_offset;
>  		inode->i_op = &shmem_symlink_inode_operations;
> @@ -3868,7 +3873,7 @@ static const char *shmem_get_link(struct dentry *dentry, struct inode *inode,
>  			return ERR_PTR(-ECHILD);
>  		}
>  	} else {
> -		error = shmem_get_folio(inode, 0, &folio, SGP_READ);
> +		error = shmem_get_folio(inode, 0, &folio, SGP_READ, PAGE_SIZE);
>  		if (error)
>  			return ERR_PTR(error);
>  		if (!folio)
> @@ -5255,7 +5260,7 @@ struct folio *shmem_read_folio_gfp(struct address_space *mapping,
>  	int error;
>  
>  	error = shmem_get_folio_gfp(inode, index, &folio, SGP_CACHE,
> -				    gfp, NULL, NULL);
> +				    gfp, NULL, NULL, PAGE_SIZE);
>  	if (error)
>  		return ERR_PTR(error);
>  
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 3c3539c573e7..540a0c2d4325 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -359,7 +359,7 @@ static int mfill_atomic_pte_continue(pmd_t *dst_pmd,
>  	struct page *page;
>  	int ret;
>  
> -	ret = shmem_get_folio(inode, pgoff, &folio, SGP_NOALLOC);
> +	ret = shmem_get_folio(inode, pgoff, &folio, SGP_NOALLOC, PAGE_SIZE);
>  	/* Our caller expects us to return -EFAULT if we failed to find folio */
>  	if (ret == -ENOENT)
>  		ret = -EFAULT;
> -- 
> 2.43.0
>