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Message-ID: <20190404150025.GN5147@magnolia> Date: Thu, 4 Apr 2019 08:00:25 -0700 From: "Darrick J. Wong" <darrick.wong@...cle.com> To: Pankaj Gupta <pagupta@...hat.com> Cc: Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>, cohuck@...hat.com, kvm@...r.kernel.org, mst@...hat.com, jasowang@...hat.com, qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org, adilger kernel <adilger.kernel@...ger.ca>, zwisler@...nel.org, aarcange@...hat.com, dave jiang <dave.jiang@...el.com>, linux-nvdimm@...ts.01.org, vishal l verma <vishal.l.verma@...el.com>, david@...hat.com, willy@...radead.org, hch@...radead.org, linux-acpi@...r.kernel.org, jmoyer@...hat.com, linux-ext4@...r.kernel.org, lenb@...nel.org, riel@...riel.com, stefanha@...hat.com, dan j williams <dan.j.williams@...el.com>, lcapitulino@...hat.com, kwolf@...hat.com, nilal@...hat.com, tytso@....edu, xiaoguangrong eric <xiaoguangrong.eric@...il.com>, rjw@...ysocki.net, linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, imammedo@...hat.com Subject: Re: [Qemu-devel] [PATCH v4 5/5] xfs: disable map_sync for async flush On Thu, Apr 04, 2019 at 06:08:44AM -0400, Pankaj Gupta wrote: > > > On Thu 04-04-19 05:09:10, Pankaj Gupta wrote: > > > > > > > > On Thu, Apr 04, 2019 at 09:09:12AM +1100, Dave Chinner wrote: > > > > > > On Wed, Apr 03, 2019 at 04:10:18PM +0530, Pankaj Gupta wrote: > > > > > > > Virtio pmem provides asynchronous host page cache flush > > > > > > > mechanism. we don't support 'MAP_SYNC' with virtio pmem > > > > > > > and xfs. > > > > > > > > > > > > > > Signed-off-by: Pankaj Gupta <pagupta@...hat.com> > > > > > > > --- > > > > > > > fs/xfs/xfs_file.c | 8 ++++++++ > > > > > > > 1 file changed, 8 insertions(+) > > > > > > > > > > > > > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > > > > > > > index 1f2e2845eb76..dced2eb8c91a 100644 > > > > > > > --- a/fs/xfs/xfs_file.c > > > > > > > +++ b/fs/xfs/xfs_file.c > > > > > > > @@ -1203,6 +1203,14 @@ xfs_file_mmap( > > > > > > > if (!IS_DAX(file_inode(filp)) && (vma->vm_flags & VM_SYNC)) > > > > > > > return -EOPNOTSUPP; > > > > > > > > > > > > > > + /* We don't support synchronous mappings with DAX files if > > > > > > > + * dax_device is not synchronous. > > > > > > > + */ > > > > > > > + if (IS_DAX(file_inode(filp)) && !dax_synchronous( > > > > > > > + xfs_find_daxdev_for_inode(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))) > > > > > > > > > > > > All this ad hoc IS_DAX conditional logic is getting pretty nasty. > > > > > > > > > > > > xfs_file_mmap( > > > > > > .... > > > > > > { > > > > > > struct inode *inode = file_inode(filp); > > > > > > > > > > > > if (vma->vm_flags & VM_SYNC) { > > > > > > if (!IS_DAX(inode)) > > > > > > return -EOPNOTSUPP; > > > > > > if (!dax_synchronous(xfs_find_daxdev_for_inode(inode)) > > > > > > return -EOPNOTSUPP; > > > > > > } > > > > > > > > > > > > file_accessed(filp); > > > > > > vma->vm_ops = &xfs_file_vm_ops; > > > > > > if (IS_DAX(inode)) > > > > > > vma->vm_flags |= VM_HUGEPAGE; > > > > > > return 0; > > > > > > } > > > > > > > > > > > > > > > > > > Even better, factor out all the "MAP_SYNC supported" checks into a > > > > > > helper so that the filesystem code just doesn't have to care about > > > > > > the details of checking for DAX+MAP_SYNC support.... > > > > > > > > > > Seconded, since ext4 has nearly the same flag validation logic. > > > > > > > > > > Only issue with this I see is we need the helper function only for > > > supported > > > filesystems ext4 & xfs (right now). If I create the function in "fs.h" it > > > will be compiled for every filesystem, even for those don't need it. > > > > > > Sample patch below, does below patch is near to what you have in mind? > > > > So I would put the helper in include/linux/dax.h and have it like: > > > > bool daxdev_mapping_supported(struct vm_area_struct *vma, Should this be static inline if you're putting it in the header file? A comment ought to be added to describe what this predicate function does. > > struct dax_device *dax_dev) > > { > > if (!(vma->vm_flags & VM_SYNC)) > > return true; > > if (!IS_DAX(file_inode(vma->vm_file))) > > return false; > > return dax_synchronous(dax_dev); > > } > > Sure. This is much better. I was also not sure what to name the helper function. > I will go ahead with this unless 'Dave' & 'Darrick' have anything to add. Jan's approach (modulo that one comment) looks good to me. --D > Thank you very much. > > Best regards, > Pankaj > > > > > Honza > > > > > > ================= > > > > > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > > > index 1f2e2845eb76..614995170cac 100644 > > > --- a/fs/xfs/xfs_file.c > > > +++ b/fs/xfs/xfs_file.c > > > @@ -1196,12 +1196,17 @@ xfs_file_mmap( > > > struct file *filp, > > > struct vm_area_struct *vma) > > > { > > > + struct dax_device *dax_dev = > > > xfs_find_daxdev_for_inode(file_inode(filp)); > > > + > > > /* > > > - * We don't support synchronous mappings for non-DAX files. At > > > least > > > - * until someone comes with a sensible use case. > > > + * We don't support synchronous mappings for non-DAX files and > > > + * for DAX files if underneath dax_device is not synchronous. > > > */ > > > - if (!IS_DAX(file_inode(filp)) && (vma->vm_flags & VM_SYNC)) > > > - return -EOPNOTSUPP; > > > + if (vma->vm_flags & VM_SYNC) { > > > + int err = is_synchronous(filp, dax_dev); > > > + if (err) > > > + return err; > > > + } > > > > > > file_accessed(filp); > > > vma->vm_ops = &xfs_file_vm_ops; > > > diff --git a/include/linux/fs.h b/include/linux/fs.h > > > index 8b42df09b04c..add017de3dd7 100644 > > > --- a/include/linux/fs.h > > > +++ b/include/linux/fs.h > > > @@ -2162,6 +2162,20 @@ static inline void file_accessed(struct file *file) > > > touch_atime(&file->f_path); > > > } > > > > > > +struct dax_device; > > > +extern bool dax_synchronous(struct dax_device *dax_dev); > > > +static inline int is_synchronous(struct file *filp, struct dax_device > > > *dax_dev) > > > +{ > > > + struct inode *inode = file_inode(filp); > > > + > > > + if (!IS_DAX(inode)) > > > + return -EOPNOTSUPP; > > > + if (!dax_synchronous(dax_dev)) > > > + return -EOPNOTSUPP; > > > + > > > + return 0; > > > +} > > > + > > > int sync_inode(struct inode *inode, struct writeback_control *wbc); > > > int sync_inode_metadata(struct inode *inode, int wait); > > > > > > --------- > > > > > > Thanks, > > > Pankaj > > > > > > > > > > > -- > > Jan Kara <jack@...e.com> > > SUSE Labs, CR > > > >
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