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From: Dave Chinner <david@fromorbit.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 14/24] xfs: remove IO submission from xfs_reclaim_inode()
Date: Mon, 25 May 2020 13:49:43 +1000
Message-ID: <20200525034943.GW2040@dread.disaster.area> (raw)
In-Reply-To: <20200522230642.GR8230@magnolia>

On Fri, May 22, 2020 at 04:06:42PM -0700, Darrick J. Wong wrote:
> On Fri, May 22, 2020 at 01:50:19PM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > We no longer need to issue IO from shrinker based inode reclaim to
> > prevent spurious OOM killer invocation. This leaves only the global
> > filesystem management operations such as unmount needing to
> > writeback dirty inodes and reclaim them.
> > 
> > Instead of using the reclaim pass to write dirty inodes before
> > reclaiming them, use the AIL to push all the dirty inodes before we
> > try to reclaim them. This allows us to remove all the conditional
> > SYNC_WAIT locking and the writeback code from xfs_reclaim_inode()
> > and greatly simplify the checks we need to do to reclaim an inode.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
> >  fs/xfs/xfs_icache.c | 116 +++++++++++---------------------------------
> >  1 file changed, 29 insertions(+), 87 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> > index 0f0f8fcd61b03..ee9bc82a0dfbe 100644
> > --- a/fs/xfs/xfs_icache.c
> > +++ b/fs/xfs/xfs_icache.c
> > @@ -1130,24 +1130,17 @@ xfs_reclaim_inode_grab(
> >   *	dirty, async	=> requeue
> >   *	dirty, sync	=> flush, wait and reclaim
> >   */
> 
> The function comment probably ought to describe what the two return
> values mean.  true when the inode was freed and false if we need to try
> again, right?

The comments are all updated in a later patch. It seemed better to
do that than to have to rewrite the repeatedly as behaviour changes
in each patch.

> > @@ -1272,20 +1219,17 @@ xfs_reclaim_inode(
> >   * then a shut down during filesystem unmount reclaim walk leak all the
> >   * unreclaimed inodes.
> >   */
> > -STATIC int
> > +static int
> 
> The function comment /really/ needs to note that the return value
> here is number of inodes that were skipped, and not just some negative
> error code.

OK, done.

> > @@ -1398,8 +1329,18 @@ xfs_reclaim_inodes(
> >  	int		mode)
> >  {
> >  	int		nr_to_scan = INT_MAX;
> > +	int		skipped;
> >  
> > -	return xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);
> > +	skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);
> > +	if (!(mode & SYNC_WAIT))
> > +		return 0;
> > +
> > +	do {
> > +		xfs_ail_push_all_sync(mp->m_ail);
> > +		skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);
> > +	} while (skipped > 0);
> > +
> > +	return 0;
> 
> Might as well kill the return value here since none of the callers care.

I think I did that in the SYNC_WAIT futzing patches that were
causing me problems and I dropped. It was in a separate patch,
anyway.

> >  }
> >  
> >  /*
> > @@ -1420,7 +1361,8 @@ xfs_reclaim_inodes_nr(
> >  	xfs_reclaim_work_queue(mp);
> >  	xfs_ail_push_all(mp->m_ail);
> >  
> > -	return xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan);
> 
> So the old code was returning negative error codes here?  Given that the
> only caller is free_cached_objects which adds it to the 'freed' count...
> wow.

Actually, no. the error from xfs_reclaim_inodes_ag() can only come
from xfs_reclaim_inode(), which always returned 0.

> > +	xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan);
> > +	return 0;
> 
> Why do we return zero freed items here?  The VFS asked us to clear
> shrink_control->nr_to_scan (passed in here as nr_to_scan) and we're
> supposed to report what we did, right?

It's the same behaviour as we currently have.

ISTR that I did the accounting this way originally so we didn't
double count inodes being freed. The inode has already been
accounted as freed by the VFS inode shrinker when it runs
->destroy_inode, so double counting every inode that is freed (once
for the VFS cache removal, once for the XFS cache removal) seemed
like a bad thing to be doing...

> Or is there some odd subtlety here where we hate the shrinker and that's
> why we return zero?

Oh, that too :P

Cheers,

Dave.

-- 
Dave Chinner
david@fromorbit.com

  reply index

Thread overview: 91+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-22  3:50 [PATCH 00/24] xfs: rework inode flushing to make inode reclaim fully asynchronous Dave Chinner
2020-05-22  3:50 ` [PATCH 01/24] xfs: remove logged flag from inode log item Dave Chinner
2020-05-22  7:25   ` Christoph Hellwig
2020-05-22 21:13   ` Darrick J. Wong
2020-05-22  3:50 ` [PATCH 02/24] xfs: add an inode item lock Dave Chinner
2020-05-22  6:45   ` Amir Goldstein
2020-05-22 21:24   ` Darrick J. Wong
2020-05-23  8:45   ` Christoph Hellwig
2020-05-22  3:50 ` [PATCH 03/24] xfs: mark inode buffers in cache Dave Chinner
2020-05-22  7:45   ` Amir Goldstein
2020-05-22 21:35   ` Darrick J. Wong
2020-05-24 23:41     ` Dave Chinner
2020-05-23  8:48   ` Christoph Hellwig
2020-05-25  0:06     ` Dave Chinner
2020-05-22  3:50 ` [PATCH 04/24] xfs: mark dquot " Dave Chinner
2020-05-22  7:46   ` Amir Goldstein
2020-05-22 21:38   ` Darrick J. Wong
2020-05-22  3:50 ` [PATCH 05/24] xfs: mark log recovery buffers for completion Dave Chinner
2020-05-22  7:41   ` Amir Goldstein
2020-05-24 23:54     ` Dave Chinner
2020-05-22 21:41   ` Darrick J. Wong
2020-05-22  3:50 ` [PATCH 06/24] xfs: call xfs_buf_iodone directly Dave Chinner
2020-05-22  7:56   ` Amir Goldstein
2020-05-22 21:53   ` Darrick J. Wong
2020-05-22  3:50 ` [PATCH 07/24] xfs: clean up whacky buffer log item list reinit Dave Chinner
2020-05-22 22:01   ` Darrick J. Wong
2020-05-23  8:50   ` Christoph Hellwig
2020-05-22  3:50 ` [PATCH 08/24] xfs: fold xfs_istale_done into xfs_iflush_done Dave Chinner
2020-05-22 22:10   ` Darrick J. Wong
2020-05-23  9:12   ` Christoph Hellwig
2020-05-22  3:50 ` [PATCH 09/24] xfs: use direct calls for dquot IO completion Dave Chinner
2020-05-22 22:13   ` Darrick J. Wong
2020-05-23  9:16   ` Christoph Hellwig
2020-05-22  3:50 ` [PATCH 10/24] xfs: clean up the buffer iodone callback functions Dave Chinner
2020-05-22 22:26   ` Darrick J. Wong
2020-05-25  0:37     ` Dave Chinner
2020-05-23  9:19   ` Christoph Hellwig
2020-05-22  3:50 ` [PATCH 11/24] xfs: get rid of log item callbacks Dave Chinner
2020-05-22 22:27   ` Darrick J. Wong
2020-05-23  9:19   ` Christoph Hellwig
2020-05-22  3:50 ` [PATCH 12/24] xfs: pin inode backing buffer to the inode log item Dave Chinner
2020-05-22 22:39   ` Darrick J. Wong
2020-05-23  9:34   ` Christoph Hellwig
2020-05-23 21:43     ` Dave Chinner
2020-05-24  5:31       ` Christoph Hellwig
2020-05-24 23:13         ` Dave Chinner
2020-05-22  3:50 ` [PATCH 13/24] xfs: make inode reclaim almost non-blocking Dave Chinner
2020-05-22 12:19   ` Amir Goldstein
2020-05-22 22:48   ` Darrick J. Wong
2020-05-23 22:29     ` Dave Chinner
2020-05-22  3:50 ` [PATCH 14/24] xfs: remove IO submission from xfs_reclaim_inode() Dave Chinner
2020-05-22 23:06   ` Darrick J. Wong
2020-05-25  3:49     ` Dave Chinner [this message]
2020-05-23  9:40   ` Christoph Hellwig
2020-05-23 22:35     ` Dave Chinner
2020-05-22  3:50 ` [PATCH 15/24] xfs: allow multiple reclaimers per AG Dave Chinner
2020-05-22 23:10   ` Darrick J. Wong
2020-05-23 22:35     ` Dave Chinner
2020-05-22  3:50 ` [PATCH 16/24] xfs: don't block inode reclaim on the ILOCK Dave Chinner
2020-05-22 23:11   ` Darrick J. Wong
2020-05-22  3:50 ` [PATCH 17/24] xfs: remove SYNC_TRYLOCK from inode reclaim Dave Chinner
2020-05-22 23:14   ` Darrick J. Wong
2020-05-23 22:42     ` Dave Chinner
2020-05-22  3:50 ` [PATCH 18/24] xfs: clean up inode reclaim comments Dave Chinner
2020-05-22 23:17   ` Darrick J. Wong
2020-05-22  3:50 ` [PATCH 19/24] xfs: attach inodes to the cluster buffer when dirtied Dave Chinner
2020-05-22 23:48   ` Darrick J. Wong
2020-05-23 22:59     ` Dave Chinner
2020-05-22  3:50 ` [PATCH 20/24] xfs: xfs_iflush() is no longer necessary Dave Chinner
2020-05-22 23:54   ` Darrick J. Wong
2020-05-22  3:50 ` [PATCH 21/24] xfs: rename xfs_iflush_int() Dave Chinner
2020-05-22 12:33   ` Amir Goldstein
2020-05-22 23:57   ` Darrick J. Wong
2020-05-22  3:50 ` [PATCH 22/24] xfs: rework xfs_iflush_cluster() dirty inode iteration Dave Chinner
2020-05-23  0:13   ` Darrick J. Wong
2020-05-23 23:14     ` Dave Chinner
2020-05-23 11:31   ` Christoph Hellwig
2020-05-23 23:23     ` Dave Chinner
2020-05-24  5:32       ` Christoph Hellwig
2020-05-23 11:39   ` Christoph Hellwig
2020-05-22  3:50 ` [PATCH 23/24] xfs: factor xfs_iflush_done Dave Chinner
2020-05-23  0:20   ` Darrick J. Wong
2020-05-23 11:35   ` Christoph Hellwig
2020-05-22  3:50 ` [PATCH 24/24] xfs: remove xfs_inobp_check() Dave Chinner
2020-05-23  0:16   ` Darrick J. Wong
2020-05-23 11:36   ` Christoph Hellwig
2020-05-22  4:04 ` [PATCH 00/24] xfs: rework inode flushing to make inode reclaim fully asynchronous Dave Chinner
2020-05-23 16:18   ` Darrick J. Wong
2020-05-23 21:22     ` Dave Chinner
2020-05-22  6:18 ` Amir Goldstein
2020-05-22 12:01   ` Amir Goldstein

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