Re: [RFC PATCH v3] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

[Shiyang Ruan]

在 2022/6/23 0:49, Darrick J. Wong 写道:
> On Wed, Jun 15, 2022 at 08:54:00PM +0800, Shiyang Ruan wrote:
> > This patch is inspired by Dan's "mm, dax, pmem: Introduce
> > dev_pagemap_failure()"[1].  With the help of dax_holder and
> > ->notify_failure() mechanism, the pmem driver is able to ask filesystem
> > (or mapped device) on it to unmap all files in use and notify processes
> > who are using those files.
> >
> > Call trace:
> > trigger unbind
> >   -> unbind_store()
> >    -> ... (skip)
> >     -> devres_release_all()   # was pmem driver ->remove() in v1
> >      -> kill_dax()
> >       -> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_REMOVE)
> >        -> xfs_dax_notify_failure()
> >
> > Introduce MF_MEM_REMOVE to let filesystem know this is a remove event.
> > So do not shutdown filesystem directly if something not supported, or if
> > failure range includes metadata area.  Make sure all files and processes
> > are handled correctly.
> >
> > [1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> >
> > Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> >
> > ==
> > Changes since v2:
> >    1. Rebased on next-20220615
> >
> > Changes since v1:
> >    1. Drop the needless change of moving {kill,put}_dax()
> >    2. Rebased on '[PATCHSETS] v14 fsdax-rmap + v11 fsdax-reflink'[2]
> >
> > ---
> >   drivers/dax/super.c         | 2 +-
> >   fs/xfs/xfs_notify_failure.c | 6 +++++-
> >   include/linux/mm.h          | 1 +
> >   3 files changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index 9b5e2a5eb0ae..d4bc83159d46 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -323,7 +323,7 @@ void kill_dax(struct dax_device *dax_dev)
> >   		return;
> >   
> >   	if (dax_dev->holder_data != NULL)
> > -		dax_holder_notify_failure(dax_dev, 0, U64_MAX, 0);
> > +		dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_REMOVE);
>
> At the point we're initiating a MEM_REMOVE call, is the pmem already
> gone, or is it about to be gone?

It's about to be gone.

I found two cases:
  1. exec `unbind` by user, who wants to unplug the pmem
  2. handle failures during initialization

> >   
> >   	clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
> >   	synchronize_srcu(&dax_srcu);
> > diff --git a/fs/xfs/xfs_notify_failure.c b/fs/xfs/xfs_notify_failure.c
> > index aa8dc27c599c..91d3f05d4241 100644
> > --- a/fs/xfs/xfs_notify_failure.c
> > +++ b/fs/xfs/xfs_notify_failure.c
> > @@ -73,7 +73,9 @@ xfs_dax_failure_fn(
> >   	struct failure_info		*notify = data;
> >   	int				error = 0;
> >   
> > -	if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
> > +	/* Do not shutdown so early when device is to be removed */
> > +	if (!(notify->mf_flags & MF_MEM_REMOVE) ||
> > +	    XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
> >   	    (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) {
> >   		xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
> >   		return -EFSCORRUPTED;
> > @@ -182,6 +184,8 @@ xfs_dax_notify_failure(
> >   
> >   	if (mp->m_logdev_targp && mp->m_logdev_targp->bt_daxdev == dax_dev &&
> >   	    mp->m_logdev_targp != mp->m_ddev_targp) {
> > +		if (mf_flags & MF_MEM_REMOVE)
> > +			return -EOPNOTSUPP;
>
> The reason I ask is that if the pmem is *about to be* but not yet
> removed from the system, shouldn't we at least try to flush all dirty
> files and the log to reduce data loss and minimize recovery time?

Yes, they should be flushed.  Will add it.


--
Thanks,
Ruan.

> If it's already gone, then you might as well shut down immediately,
> unless there's a chance the pmem will come back(?)
>
> --D
>
> >   		xfs_err(mp, "ondisk log corrupt, shutting down fs!");
> >   		xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
> >   		return -EFSCORRUPTED;
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 623c2ee8330a..bbeb31883362 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -3249,6 +3249,7 @@ enum mf_flags {
> >   	MF_SOFT_OFFLINE = 1 << 3,
> >   	MF_UNPOISON = 1 << 4,
> >   	MF_NO_RETRY = 1 << 5,
> > +	MF_MEM_REMOVE = 1 << 6,
> >   };
> >   int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
> >   		      unsigned long count, int mf_flags);
> > --
> > 2.36.1