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From: Ira Weiny <ira.weiny@intel.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-kernel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@lst.de>,
	"Theodore Y. Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
	linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [RFC PATCH V2 08/12] fs/xfs: Add lock/unlock mode to xfs
Date: Wed, 15 Jan 2020 15:52:37 -0800
Message-ID: <20200115235237.GA24522@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200113221957.GN8247@magnolia>

On Mon, Jan 13, 2020 at 02:19:57PM -0800, Darrick J. Wong wrote:
> On Fri, Jan 10, 2020 at 11:29:38AM -0800, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.com>
> > 

[snip]

> >  
> > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> > index 401da197f012..e8fd95b75e5b 100644
> > --- a/fs/xfs/xfs_inode.c
> > +++ b/fs/xfs/xfs_inode.c
> > @@ -142,12 +142,12 @@ xfs_ilock_attr_map_shared(
> >   *
> >   * Basic locking order:
> >   *
> > - * i_rwsem -> i_mmap_lock -> page_lock -> i_ilock
> > + * i_rwsem -> i_dax_sem -> i_mmap_lock -> page_lock -> i_ilock
> 
> Mmmmmm, more locks.  Can we skip the extra lock if CONFIG_FSDAX=n or if
> the filesystem devices don't support DAX at all?

I've looked into this a bit more and I think skipping on CONFIG_FSDAX=n is ok
but doing so on individual devices is not going to be possible because we don't
have that information at the vfs layer.

I'll continue to think about how to mitigate this more while I add CONFIG_FSDAX
checks before rolling out a new patch set.

> 
> Also, I don't think we're actually following the i_rwsem -> i_daxsem
> order in fallocate, and possibly elsewhere too?
> 
> Does the vfs have to take the i_dax_sem to do remapping things like
> reflink?  (Pretend that reflink and dax are compatible for the moment)
> 

I spoke with Dan today about this and we believe the answer is going to be yes.
However, not until the code is added to support DAX in reflink.  Because
currently this is only required for places which use "IS_DAX()" to see the
state of the inode.

Currently the vfs layer does not have any IS_DAX() checks in the reflink path.
But when they are added they will be required to take this sem.

Ira


  parent reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-10 19:29 [RFC PATCH V2 00/12] Enable per-file/directory DAX operations V2 ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 01/12] fs/stat: Define DAX statx attribute ira.weiny
2020-01-15 11:37   ` Jan Kara
2020-01-15 17:38     ` Darrick J. Wong
2020-01-15 19:45       ` Ira Weiny
2020-01-15 20:10         ` Dan Williams
2020-01-15 22:38           ` Ira Weiny
2020-01-16  5:39             ` Darrick J. Wong
2020-01-16  6:05               ` Dan Williams
2020-01-16  6:18                 ` Darrick J. Wong
2020-01-16  6:25                   ` Dan Williams
2020-01-16 17:55               ` Ira Weiny
2020-01-16 18:04                 ` Darrick J. Wong
2020-01-16 18:52                   ` Ira Weiny
2020-01-16 22:19                     ` Darrick J. Wong
2020-01-17 11:58                     ` Jan Kara
2020-01-10 19:29 ` [RFC PATCH V2 02/12] fs/xfs: Isolate the physical DAX flag from effective ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 03/12] fs/xfs: Separate functionality of xfs_inode_supports_dax() ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 04/12] fs/xfs: Clean up DAX support check ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 05/12] fs: remove unneeded IS_DAX() check ira.weiny
2020-01-16  9:38   ` Jan Kara
2020-01-16 18:47     ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 06/12] fs/xfs: Check if the inode supports DAX under lock ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 07/12] fs: Add locking for a dynamic inode 'mode' ira.weiny
2020-01-13 22:12   ` Darrick J. Wong
2020-01-14  0:20     ` Ira Weiny
2020-01-14  1:03       ` Darrick J. Wong
2020-01-15 19:08         ` Ira Weiny
2020-01-16  5:40           ` Darrick J. Wong
2020-01-16 18:54             ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 08/12] fs/xfs: Add lock/unlock mode to xfs ira.weiny
2020-01-13 22:19   ` Darrick J. Wong
2020-01-14  0:35     ` Ira Weiny
2020-01-15  0:57       ` Ira Weiny
2020-01-15 23:52     ` Ira Weiny [this message]
2020-01-16  9:24   ` Jan Kara
2020-01-16 19:12     ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 09/12] fs: Prevent mode change if file is mmap'ed ira.weiny
2020-01-13 22:22   ` Darrick J. Wong
2020-01-14  0:46     ` Ira Weiny
2020-01-14  1:30       ` Darrick J. Wong
2020-01-14 17:53         ` Ira Weiny
2020-01-15 11:34           ` Jan Kara
2020-01-15 18:24             ` Ira Weiny
2020-01-15 10:21   ` David Laight
2020-01-15 17:53     ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 10/12] fs/xfs: Fix truncate up ira.weiny
2020-01-13 22:27   ` Darrick J. Wong
2020-01-14  0:40     ` Ira Weiny
2020-01-14  1:14       ` Darrick J. Wong
2020-01-14 19:00         ` Ira Weiny
2020-01-14 19:39           ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 11/12] fs/xfs: Clean up locking in dax invalidate ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 12/12] fs/xfs: Allow toggle of effective DAX flag ira.weiny

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