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

[Darrick J. Wong]

On Wed, Nov 01, 2017 at 04:36:47PM +0100, Jan Kara wrote:
> From: Christoph Hellwig 
> 
> 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 
> Signed-off-by: Christoph Hellwig 
> Signed-off-by: Jan Kara 

Looks ok,
Reviewed-by: Darrick J. Wong 

> ---
>  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 
>  #include 
>  #include 
> +#include 
>  
>  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, _iomap_ops);
> + pfn_t pfn;
> +
> + ret = dax_iomap_fault(vmf, pe_size, , _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, _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 = _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, );
>   }
>  
> + 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, );
>  
>   if (shared)
> -- 
> 2.12.3
> 
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[PATCH 18/18] xfs: support for synchronous DAX faults

[Jan Kara]

From: Christoph Hellwig 

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 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Jan Kara 
---
 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 
 #include 
 #include 
+#include 
 
 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, _iomap_ops);
+   pfn_t pfn;
+
+   ret = dax_iomap_fault(vmf, pe_size, , _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, _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 = _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, );
}
 
+   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, );
 
if (shared)
-- 
2.12.3

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