Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1585790

Re: [PATCH 2/7] fs, xfs: convert xfs_buf.b_hold and xfs_buf.b_lru_ref from atomic_t to refcount_t

Show all headers | View raw

On Tue, Feb 21, 2017 at 05:04:08PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 21, 2017 at 05:49:02PM +0200, Elena Reshetova wrote:
> > @@ -1684,10 +1684,11 @@ xfs_buftarg_isolate(
> >  	 * zero. If the value is already zero, we need to reclaim the
> >  	 * buffer, otherwise it gets another trip through the LRU.
> >  	 */
> > -	if (!atomic_add_unless(&bp->b_lru_ref, -1, 0)) {
> > +	if (!refcount_read(&bp->b_lru_ref)) {
> >  		spin_unlock(&bp->b_lock);
> >  		return LRU_ROTATE;
> >  	}
> > +	refcount_dec_and_test(&bp->b_lru_ref);
> >  
> >  	bp->b_state |= XFS_BSTATE_DISPOSE;
> >  	list_lru_isolate_move(lru, item, dispose);
> 
> This should never have passed testing.. refcount_dec_and_test() has a
> __must_check.
> 
> Furthermore the above seems to suggest thingies can live with a 0
> refcount, so a straight conversion cannot work.

Yes, 0 is a valid value - the buffer lru reference is *not an object
lifecycle reference count*. A value of zero means reclaim needs to
take action if it sees that value - it does not mean that the object
is not referenced by anyone (that's b_hold). i.e.  b_lru_ref is an
"active reference weighting" used to provide a heirarchical reclaim
bias toward less important metadata objects, and has no bearing on
the actual active users of the object.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 0/7] fs, xfs subsystem refcounter conversions Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 16:50 +0100
  [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 16:50 +0100
    Re: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-02-21 17:40 +0100
      RE: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-22 12:20 +0100
    Re: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t Dave Chinner <david@fromorbit.com> - 2017-02-22 00:00 +0100
      RE: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-22 12:30 +0100
        Re: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t Dave Chinner <david@fromorbit.com> - 2017-02-22 23:10 +0100
          RE: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-23 09:00 +0100
  [PATCH 5/7] fs, xfs: convert xlog_ticket.t_ref from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
  Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-02-21 17:00 +0100
    RE: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-21 17:10 +0100
      Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-02-21 17:30 +0100
        Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-02-21 17:40 +0100
      Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-02-21 18:10 +0100
        Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t Brian Foster <bfoster@redhat.com> - 2017-02-21 20:30 +0100
          RE: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-22 12:30 +0100
  [PATCH 7/7] fs, xfs: convert xfs_rui_log_item.rui_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
  [PATCH 4/7] fs, xfs: convert xfs_efi_log_item.efi_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
  [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
  [PATCH 2/7] fs, xfs: convert xfs_buf.b_hold and xfs_buf.b_lru_ref from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
    Re: [PATCH 2/7] fs, xfs: convert xfs_buf.b_hold and  xfs_buf.b_lru_ref from atomic_t to refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-02-21 17:10 +0100
      Re: [PATCH 2/7] fs, xfs: convert xfs_buf.b_hold and  xfs_buf.b_lru_ref from atomic_t to refcount_t Dave Chinner <david@fromorbit.com> - 2017-02-22 00:00 +0100
        RE: [PATCH 2/7] fs, xfs: convert xfs_buf.b_hold and  xfs_buf.b_lru_ref from atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-22 12:20 +0100
  [PATCH 6/7] fs, xfs: convert xfs_cui_log_item.cui_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100

csiph-web