linux-ext4 - Re: [PATCH 18/18] xfs: support for synchronous DAX faults

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Date:   Mon, 13 Nov 2017 18:19:42 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-mm@...ck.org, linux-api@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 18/18] xfs: support for synchronous DAX faults

On Wed, Nov 01, 2017 at 04:36:47PM +0100, Jan Kara wrote:
> From: Christoph Hellwig <hch@....de>
> 
> Return IOMAP_F_DIRTY from xfs_file_iomap_begin() when asked to prepare
> blocks for writing and the inode is pinned, and has dirty fields other
> than the timestamps.  In __xfs_filemap_fault() we then detect this case
> and call dax_finish_sync_fault() to make sure all metadata is committed,
> and to insert the page table entry.
> 
> Note that this will also dirty corresponding radix tree entry which is
> what we want - fsync(2) will still provide data integrity guarantees for
> applications not using userspace flushing. And applications using
> userspace flushing can avoid calling fsync(2) and thus avoid the
> performance overhead.
> 
> [JK: Added VM_SYNC flag handling]
> 
> Reviewed-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Signed-off-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Jan Kara <jack@...e.cz>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>

> ---
>  fs/xfs/xfs_file.c  | 15 ++++++++++++++-
>  fs/xfs/xfs_iomap.c |  5 +++++
>  2 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 4496b45678de..4827e82d5d2c 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -44,6 +44,7 @@
>  #include <linux/falloc.h>
>  #include <linux/pagevec.h>
>  #include <linux/backing-dev.h>
> +#include <linux/mman.h>
>  
>  static const struct vm_operations_struct xfs_file_vm_ops;
>  
> @@ -1040,7 +1041,11 @@ __xfs_filemap_fault(
>  
>  	xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
>  	if (IS_DAX(inode)) {
> -		ret = dax_iomap_fault(vmf, pe_size, NULL, &xfs_iomap_ops);
> +		pfn_t pfn;
> +
> +		ret = dax_iomap_fault(vmf, pe_size, &pfn, &xfs_iomap_ops);
> +		if (ret & VM_FAULT_NEEDDSYNC)
> +			ret = dax_finish_sync_fault(vmf, pe_size, pfn);
>  	} else {
>  		if (write_fault)
>  			ret = iomap_page_mkwrite(vmf, &xfs_iomap_ops);
> @@ -1110,6 +1115,13 @@ xfs_file_mmap(
>  	struct file	*filp,
>  	struct vm_area_struct *vma)
>  {
> +	/*
> +	 * We don't support synchronous mappings for non-DAX files. At least
> +	 * until someone comes with a sensible use case.
> +	 */
> +	if (!IS_DAX(file_inode(filp)) && (vma->vm_flags & VM_SYNC))
> +		return -EOPNOTSUPP;
> +
>  	file_accessed(filp);
>  	vma->vm_ops = &xfs_file_vm_ops;
>  	if (IS_DAX(file_inode(filp)))
> @@ -1128,6 +1140,7 @@ const struct file_operations xfs_file_operations = {
>  	.compat_ioctl	= xfs_file_compat_ioctl,
>  #endif
>  	.mmap		= xfs_file_mmap,
> +	.mmap_supported_flags = MAP_SYNC,
>  	.open		= xfs_file_open,
>  	.release	= xfs_file_release,
>  	.fsync		= xfs_file_fsync,
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index f179bdf1644d..b43be199fbdf 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -33,6 +33,7 @@
>  #include "xfs_error.h"
>  #include "xfs_trans.h"
>  #include "xfs_trans_space.h"
> +#include "xfs_inode_item.h"
>  #include "xfs_iomap.h"
>  #include "xfs_trace.h"
>  #include "xfs_icache.h"
> @@ -1086,6 +1087,10 @@ xfs_file_iomap_begin(
>  		trace_xfs_iomap_found(ip, offset, length, 0, &imap);
>  	}
>  
> +	if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) &&
> +	    (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
> +		iomap->flags |= IOMAP_F_DIRTY;
> +
>  	xfs_bmbt_to_iomap(ip, iomap, &imap);
>  
>  	if (shared)
> -- 
> 2.12.3
> 
> --
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