Re: [PATCH 2/3] xfs: drop IDONTCACHE on inodes when we mark them sick

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Jun 03, 2021 at 02:34:46PM +1000, Dave Chinner wrote:
> On Wed, Jun 02, 2021 at 08:12:46PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > When we decide to mark an inode sick, clear the DONTCACHE flag so that
> > the incore inode will be kept around until memory pressure forces it out
> > of memory.  This increases the chances that the sick status will be
> > caught by someone compiling a health report later on.
> > 
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > ---
> >  fs/xfs/xfs_health.c |    5 +++++
> >  fs/xfs/xfs_icache.c |    3 ++-
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> > 
> > 
> > diff --git a/fs/xfs/xfs_health.c b/fs/xfs/xfs_health.c
> > index 8e0cb05a7142..824e0b781290 100644
> > --- a/fs/xfs/xfs_health.c
> > +++ b/fs/xfs/xfs_health.c
> > @@ -231,6 +231,11 @@ xfs_inode_mark_sick(
> >  	ip->i_sick |= mask;
> >  	ip->i_checked |= mask;
> >  	spin_unlock(&ip->i_flags_lock);
> > +
> > +	/* Keep this inode around so we don't lose the sickness report. */
> > +	spin_lock(&VFS_I(ip)->i_lock);
> > +	VFS_I(ip)->i_state &= ~I_DONTCACHE;
> > +	spin_unlock(&VFS_I(ip)->i_lock);
> >  }
> 
> Dentries will still be reclaimed, but the VFS will at least hold on
> to the inode in this case.

Right.

> >  /* Mark parts of an inode healed. */
> > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> > index c3f912a9231b..0e2b6c05e604 100644
> > --- a/fs/xfs/xfs_icache.c
> > +++ b/fs/xfs/xfs_icache.c
> > @@ -23,6 +23,7 @@
> >  #include "xfs_dquot.h"
> >  #include "xfs_reflink.h"
> >  #include "xfs_ialloc.h"
> > +#include "xfs_health.h"
> >  
> >  #include <linux/iversion.h>
> >  
> > @@ -648,7 +649,7 @@ xfs_iget_cache_miss(
> >  	 * time.
> >  	 */
> >  	iflags = XFS_INEW;
> > -	if (flags & XFS_IGET_DONTCACHE)
> > +	if ((flags & XFS_IGET_DONTCACHE) && xfs_inode_is_healthy(ip))
> 
> Hmmmm. xfs_inode_is_healthy() is kind of heavyweight for just
> checking that ip->i_sick == 0. At this point, nobody else can be
> accessing the inode, so we don't need masks nor a spinlock for
> checking the sick field.
> 
> So why not:
> 
> 	if ((flags & XFS_IGET_DONTCACHE) && !READ_ONCE(ip->i_sick))
> 
> Or maybe still use xfs_inode_is_healthy() but convert it to the
> simpler, lockless sick check?

As Brian points out, it's totally unnecessary.

--D

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com