Re: [PATCH 2/4] xfs: split write fault handling out of __xfs_filemap_fault

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

On Tue, Oct 29, 2024 at 04:11:58PM +0100, Christoph Hellwig wrote:
> Only two of the callers of __xfs_filemap_fault every handle read faults.
> Split the write_fault handling out of __xfs_filemap_fault so that all
> callers call that directly either conditionally or unconditionally and
> only leave the read fault handling in __xfs_filemap_fault.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

This seems pretty straightforward so
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/xfs/xfs_file.c | 41 +++++++++++++++++++----------------------
>  1 file changed, 19 insertions(+), 22 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 20f7f92b8867..0b8e36f8703c 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1434,6 +1434,16 @@ xfs_dax_read_fault(
>  	return ret;
>  }
>  
> +/*
> + * Locking for serialisation of IO during page faults. This results in a lock
> + * ordering of:
> + *
> + * mmap_lock (MM)
> + *   sb_start_pagefault(vfs, freeze)
> + *     invalidate_lock (vfs/XFS_MMAPLOCK - truncate serialisation)
> + *       page_lock (MM)
> + *         i_lock (XFS - extent map serialisation)
> + */
>  static vm_fault_t
>  xfs_write_fault(
>  	struct vm_fault		*vmf,
> @@ -1471,26 +1481,13 @@ xfs_write_fault(
>  	return ret;
>  }
>  
> -/*
> - * Locking for serialisation of IO during page faults. This results in a lock
> - * ordering of:
> - *
> - * mmap_lock (MM)
> - *   sb_start_pagefault(vfs, freeze)
> - *     invalidate_lock (vfs/XFS_MMAPLOCK - truncate serialisation)
> - *       page_lock (MM)
> - *         i_lock (XFS - extent map serialisation)
> - */
>  static vm_fault_t
>  __xfs_filemap_fault(
>  	struct vm_fault		*vmf,
> -	unsigned int		order,
> -	bool			write_fault)
> +	unsigned int		order)
>  {
>  	struct inode		*inode = file_inode(vmf->vma->vm_file);
>  
> -	if (write_fault)
> -		return xfs_write_fault(vmf, order);
>  	if (IS_DAX(inode))
>  		return xfs_dax_read_fault(vmf, order);
>  
> @@ -1511,9 +1508,9 @@ xfs_filemap_fault(
>  	struct vm_fault		*vmf)
>  {
>  	/* DAX can shortcut the normal fault path on write faults! */
> -	return __xfs_filemap_fault(vmf, 0,
> -			IS_DAX(file_inode(vmf->vma->vm_file)) &&
> -			xfs_is_write_fault(vmf));
> +	if (IS_DAX(file_inode(vmf->vma->vm_file)) && xfs_is_write_fault(vmf))
> +		return xfs_write_fault(vmf, 0);
> +	return __xfs_filemap_fault(vmf, 0);
>  }
>  
>  static vm_fault_t
> @@ -1525,15 +1522,16 @@ xfs_filemap_huge_fault(
>  		return VM_FAULT_FALLBACK;
>  
>  	/* DAX can shortcut the normal fault path on write faults! */
> -	return __xfs_filemap_fault(vmf, order,
> -			xfs_is_write_fault(vmf));
> +	if (xfs_is_write_fault(vmf))
> +		return xfs_write_fault(vmf, order);
> +	return __xfs_filemap_fault(vmf, order);
>  }
>  
>  static vm_fault_t
>  xfs_filemap_page_mkwrite(
>  	struct vm_fault		*vmf)
>  {
> -	return __xfs_filemap_fault(vmf, 0, true);
> +	return xfs_write_fault(vmf, 0);
>  }
>  
>  /*
> @@ -1545,8 +1543,7 @@ static vm_fault_t
>  xfs_filemap_pfn_mkwrite(
>  	struct vm_fault		*vmf)
>  {
> -
> -	return __xfs_filemap_fault(vmf, 0, true);
> +	return xfs_write_fault(vmf, 0);
>  }
>  
>  static const struct vm_operations_struct xfs_file_vm_ops = {
> -- 
> 2.45.2
> 
>