Re: [PATCH-v5 0/5] add support for a lazytime mount option

[Jan Kara <jack@suse.cz>]

On Fri 28-11-14 09:55:19, Sedat Dilek wrote:
> On Fri, Nov 28, 2014 at 7:00 AM, Theodore Ts'o <tytso@mit.edu> wrote:
> > This is an updated version of what had originally been an
> > ext4-specific patch which significantly improves performance by lazily
> > writing timestamp updates (and in particular, mtime updates) to disk.
> > The in-memory timestamps are always correct, but they are only written
> > to disk when required for correctness.
> >
> > This provides a huge performance boost for ext4 due to how it handles
> > journalling, but it's valuable for all file systems running on flash
> > storage or drive-managed SMR disks by reducing the metadata write
> > load.  So upon request, I've moved the functionality to the VFS layer.
> > Once the /sbin/mount program adds support for MS_LAZYTIME, all file
> > systems should be able to benefit from this optimization.
> >
> > There is still an ext4-specific optimization, which may be applicable
> > for other file systems which store more than one inode in a block, but
> > it will require file system specific code.  It is purely optional,
> > however.
> >
> > Please note the changes to update_time() and the new write_time() inode
> > operations functions, which impact btrfs and xfs.  The changes are
> > fairly simple, but I would appreciate confirmation from the btrfs and
> > xfs teams that I got things right.   Thanks!!
> >
> 
> Some questions... on how to test this...
> 
> [ Base ]
> Is this patchset on top of ext4-next (ext4.git#dev)? Might someone
> test on top of Linux v3.18-rc6 with pulled in ext4.git#dev2?
> 
> [ Userland ]
> Do I need an updated userland (/sbin/mount)? IOW, adding "lazytime" to
> my ext4-line(s) in /etc/fstab is enough?
> 
> [ Benchmarks ]
> Do you have numbers - how big/fast is the benefit? On a desktop machine?
  Actually a benefit you may notice on a laptop machine is that disk will
wake up less often. When I was looking for reasons of disk wakeup on a
desktop machine, some of these were mtime updates of unix socket inodes.
This patches will make them go away.

								Honza

> 
> Thanks in advance.
> 
> - Sedat -
> 
> > Changes since -v4:
> >    - Fix ext4 optimization so it does not need to increment (and more
> >      problematically, decrement) the inode reference count
> >    - Per Christoph's suggestion, drop support for btrfs and xfs for now,
> >      issues with how btrfs and xfs handle dirty inode tracking.  We can add
> >      btrfs and xfs support back later or at the end of this series if we
> >      want to revisit this decision.
> >    - Miscellaneous cleanups
> >
> > Changes since -v3:
> >    - inodes with I_DIRTY_TIME set are placed on a new bdi list,
> >         b_dirty_time.  This allows filesystem-level syncs to more
> >         easily iterate over those inodes that need to have their
> >         timestamps written to disk.
> >    - dirty timestamps will be written out asynchronously on the final
> >         iput, instead of when the inode gets evicted.
> >    - separate the definition of the new function
> >         find_active_inode_nowait() to a separate patch
> >    - create separate flag masks: I_DIRTY_WB and I_DIRTY_INODE, which
> >        indicate whether the inode needs to be on the write back lists,
> >        or whether the inode itself is dirty, while I_DIRTY means any one
> >        of the inode dirty flags are set.  This simplifies the fs
> >        writeback logic which needs to test for different combinations of
> >        the inode dirty flags in different places.
> >
> > Changes since -v2:
> >    - If update_time() updates i_version, it will not use lazytime (i..e,
> >        the inode will be marked dirty so the change will be persisted on to
> >        disk sooner rather than later).  Yes, this eliminates the
> >        benefits of lazytime if the user is experting the file system via
> >        NFSv4.  Sad, but NFS's requirements seem to mandate this.
> >    - Fix time wrapping bug 49 days after the system boots (on a system
> >         with a 32-bit jiffies).   Use get_monotonic_boottime() instead.
> >    - Clean up type warning in include/tracing/ext4.h
> >    - Added explicit parenthesis for stylistic reasons
> >    - Added an is_readonly() inode operations method so btrfs doesn't
> >        have to duplicate code in update_time().
> >
> > Changes since -v1:
> >    - Added explanatory comments in update_time() regarding i_ts_dirty_days
> >    - Fix type used for days_since_boot
> >    - Improve SMP scalability in update_time and ext4_update_other_inodes_time
> >    - Added tracepoints to help test and characterize how often and under
> >          what circumstances inodes have their timestamps lazily updated
> >
> > Theodore Ts'o (5):
> >   vfs: add support for a lazytime mount option
> >   vfs: don't let the dirty time inodes get more than a day stale
> >   vfs: add lazytime tracepoints for better debugging
> >   vfs: add find_inode_nowait() function
> >   ext4: add optimization for the lazytime mount option
> >
> >  fs/ext4/inode.c             |  66 +++++++++++++++++++++++--
> >  fs/ext4/super.c             |   9 ++++
> >  fs/fs-writeback.c           |  66 ++++++++++++++++++++++---
> >  fs/inode.c                  | 116 +++++++++++++++++++++++++++++++++++++++++---
> >  fs/libfs.c                  |   2 +-
> >  fs/logfs/readwrite.c        |   2 +-
> >  fs/nfsd/vfs.c               |   2 +-
> >  fs/pipe.c                   |   2 +-
> >  fs/proc_namespace.c         |   1 +
> >  fs/sync.c                   |   8 +++
> >  fs/ufs/truncate.c           |   2 +-
> >  include/linux/backing-dev.h |   1 +
> >  include/linux/fs.h          |  17 ++++++-
> >  include/trace/events/ext4.h |  30 ++++++++++++
> >  include/trace/events/fs.h   |  56 +++++++++++++++++++++
> >  include/uapi/linux/fs.h     |   1 +
> >  mm/backing-dev.c            |  10 +++-
> >  17 files changed, 367 insertions(+), 24 deletions(-)
> >  create mode 100644 include/trace/events/fs.h
> >
> > --
> > 2.1.0
> >
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-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR