linux-kernel - Re: [PATCH 7/8] xfs: Support for transparent PUD pages

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Date:	Thu, 31 Dec 2015 10:30:27 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc:	Matthew Wilcox <willy@...ux.intel.com>, linux-mm@...ck.org,
	linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 7/8] xfs: Support for transparent PUD pages

On Thu, Dec 24, 2015 at 11:20:36AM -0500, Matthew Wilcox wrote:
> From: Matthew Wilcox <willy@...ux.intel.com>
> 
> Call into DAX to provide support for PUD pages, just like the PMD cases.
> 
> Signed-off-by: Matthew Wilcox <willy@...ux.intel.com>
> ---
>  fs/xfs/xfs_file.c  | 33 +++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_trace.h |  1 +
>  2 files changed, 34 insertions(+)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index f5392ab..a81b942 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1600,6 +1600,38 @@ xfs_filemap_pmd_fault(
>  	return ret;
>  }
>  
> +STATIC int
> +xfs_filemap_pud_fault(
> +	struct vm_area_struct	*vma,
> +	unsigned long		addr,
> +	pud_t			*pud,
> +	unsigned int		flags)
> +{
> +	struct inode		*inode = file_inode(vma->vm_file);
> +	struct xfs_inode	*ip = XFS_I(inode);
> +	int			ret;
> +
> +	if (!IS_DAX(inode))
> +		return VM_FAULT_FALLBACK;
> +
> +	trace_xfs_filemap_pud_fault(ip);
> +
> +	if (flags & FAULT_FLAG_WRITE) {
> +		sb_start_pagefault(inode->i_sb);
> +		file_update_time(vma->vm_file);
> +	}
> +
> +	xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> +	ret = __dax_pud_fault(vma, addr, pud, flags, xfs_get_blocks_dax_fault,
> +			      NULL);
> +	xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> +
> +	if (flags & FAULT_FLAG_WRITE)
> +		sb_end_pagefault(inode->i_sb);
> +
> +	return ret;
> +}
> +
>  /*
>   * pfn_mkwrite was originally inteneded to ensure we capture time stamp
>   * updates on write faults. In reality, it's need to serialise against
> @@ -1637,6 +1669,7 @@ xfs_filemap_pfn_mkwrite(
>  static const struct vm_operations_struct xfs_file_vm_ops = {
>  	.fault		= xfs_filemap_fault,
>  	.pmd_fault	= xfs_filemap_pmd_fault,
> +	.pud_fault	= xfs_filemap_pud_fault,

This is getting silly - we now have 3 different page fault handlers
that all do exactly the same thing. Please abstract this so that the
page/pmd/pud is transparent and gets passed through to the generic
handler code that then handles the differences between page/pmd/pud
internally.

This, after all, is the original reason that the ->fault handler was
introduced....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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