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From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 18/24] xfs: clean up inode reclaim comments
Date: Fri, 22 May 2020 16:17:47 -0700
Message-ID: <20200522231747.GV8230@magnolia> (raw)
In-Reply-To: <20200522035029.3022405-19-david@fromorbit.com>

On Fri, May 22, 2020 at 01:50:23PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Inode reclaim is quite different now to the way described in various
> comments, so update all the comments explaining what it does and how
> it works.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_icache.c | 128 ++++++++++++--------------------------------
>  1 file changed, 35 insertions(+), 93 deletions(-)
> 
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index 8b366bc7b53c9..81c23384d3310 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -141,11 +141,8 @@ xfs_inode_free(
>  }
>  
>  /*
> - * Queue a new inode reclaim pass if there are reclaimable inodes and there
> - * isn't a reclaim pass already in progress. By default it runs every 5s based
> - * on the xfs periodic sync default of 30s. Perhaps this should have it's own
> - * tunable, but that can be done if this method proves to be ineffective or too
> - * aggressive.
> + * Queue background inode reclaim work if there are reclaimable inodes and there
> + * isn't reclaim work already scheduled or in progress.
>   */
>  static void
>  xfs_reclaim_work_queue(
> @@ -164,8 +161,7 @@ xfs_reclaim_work_queue(
>   * This is a fast pass over the inode cache to try to get reclaim moving on as
>   * many inodes as possible in a short period of time. It kicks itself every few
>   * seconds, as well as being kicked by the inode cache shrinker when memory
> - * goes low. It scans as quickly as possible avoiding locked inodes or those
> - * already being flushed, and once done schedules a future pass.
> + * goes low.
>   */
>  void
>  xfs_reclaim_worker(
> @@ -618,48 +614,31 @@ xfs_iget_cache_miss(
>  }
>  
>  /*
> - * Look up an inode by number in the given file system.
> - * The inode is looked up in the cache held in each AG.
> - * If the inode is found in the cache, initialise the vfs inode
> - * if necessary.
> + * Look up an inode by number in the given file system.  The inode is looked up
> + * in the cache held in each AG.  If the inode is found in the cache, initialise
> + * the vfs inode if necessary.
>   *
> - * If it is not in core, read it in from the file system's device,
> - * add it to the cache and initialise the vfs inode.
> + * If it is not in core, read it in from the file system's device, add it to the
> + * cache and initialise the vfs inode.
>   *
>   * The inode is locked according to the value of the lock_flags parameter.
> - * This flag parameter indicates how and if the inode's IO lock and inode lock
> - * should be taken.
> - *
> - * mp -- the mount point structure for the current file system.  It points
> - *       to the inode hash table.
> - * tp -- a pointer to the current transaction if there is one.  This is
> - *       simply passed through to the xfs_iread() call.
> - * ino -- the number of the inode desired.  This is the unique identifier
> - *        within the file system for the inode being requested.
> - * lock_flags -- flags indicating how to lock the inode.  See the comment
> - *		 for xfs_ilock() for a list of valid values.
> + * Inode lookup is only done during metadata operations and not as part of the
> + * data IO path. Hence we only allow locking of the XFS_ILOCK during lookup.
>   */
>  int
>  xfs_iget(
> -	xfs_mount_t	*mp,
> -	xfs_trans_t	*tp,
> -	xfs_ino_t	ino,
> -	uint		flags,
> -	uint		lock_flags,
> -	xfs_inode_t	**ipp)
> +	struct xfs_mount	*mp,
> +	struct xfs_trans	*tp,
> +	xfs_ino_t		ino,
> +	uint			flags,
> +	uint			lock_flags,
> +	struct xfs_inode	**ipp)
>  {
> -	xfs_inode_t	*ip;
> -	int		error;
> -	xfs_perag_t	*pag;
> -	xfs_agino_t	agino;
> +	struct xfs_inode	*ip;
> +	struct xfs_perag	*pag;
> +	xfs_agino_t		agino;
> +	int			error;
>  
> -	/*
> -	 * xfs_reclaim_inode() uses the ILOCK to ensure an inode
> -	 * doesn't get freed while it's being referenced during a
> -	 * radix tree traversal here.  It assumes this function
> -	 * aqcuires only the ILOCK (and therefore it has no need to
> -	 * involve the IOLOCK in this synchronization).
> -	 */
>  	ASSERT((lock_flags & (XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED)) == 0);
>  
>  	/* reject inode numbers outside existing AGs */
> @@ -771,15 +750,7 @@ xfs_inode_ag_walk_grab(
>  
>  	ASSERT(rcu_read_lock_held());
>  
> -	/*
> -	 * check for stale RCU freed inode
> -	 *
> -	 * If the inode has been reallocated, it doesn't matter if it's not in
> -	 * the AG we are walking - we are walking for writeback, so if it
> -	 * passes all the "valid inode" checks and is dirty, then we'll write
> -	 * it back anyway.  If it has been reallocated and still being
> -	 * initialised, the XFS_INEW check below will catch it.
> -	 */
> +	/* Check for stale RCU freed inode */
>  	spin_lock(&ip->i_flags_lock);
>  	if (!ip->i_ino)
>  		goto out_unlock_noent;
> @@ -1089,43 +1060,16 @@ xfs_reclaim_inode_grab(
>  }
>  
>  /*
> - * Inodes in different states need to be treated differently. The following
> - * table lists the inode states and the reclaim actions necessary:
> - *
> - *	inode state	     iflush ret		required action
> - *      ---------------      ----------         ---------------
> - *	bad			-		reclaim
> - *	shutdown		EIO		unpin and reclaim
> - *	clean, unpinned		0		reclaim
> - *	stale, unpinned		0		reclaim
> - *	clean, pinned(*)	0		requeue
> - *	stale, pinned		EAGAIN		requeue
> - *	dirty, async		-		requeue
> - *	dirty, sync		0		reclaim
> + * Inode reclaim is non-blocking, so the default action if progress cannot be
> + * made is to "requeue" the inode for reclaim by unlocking it and clearing the
> + * XFS_IRECLAIM flag.  If we are in a shutdown state, we don't care about
> + * blocking anymore and hence we can wait for the inode to be able to reclaim
> + * it.
>   *
> - * (*) dgc: I don't think the clean, pinned state is possible but it gets
> - * handled anyway given the order of checks implemented.
> - *
> - * Also, because we get the flush lock first, we know that any inode that has
> - * been flushed delwri has had the flush completed by the time we check that
> - * the inode is clean.
> - *
> - * Note that because the inode is flushed delayed write by AIL pushing, the
> - * flush lock may already be held here and waiting on it can result in very
> - * long latencies.  Hence for sync reclaims, where we wait on the flush lock,
> - * the caller should push the AIL first before trying to reclaim inodes to
> - * minimise the amount of time spent waiting.  For background relaim, we only
> - * bother to reclaim clean inodes anyway.
> - *
> - * Hence the order of actions after gaining the locks should be:
> - *	bad		=> reclaim
> - *	shutdown	=> unpin and reclaim
> - *	pinned, async	=> requeue
> - *	pinned, sync	=> unpin
> - *	stale		=> reclaim
> - *	clean		=> reclaim
> - *	dirty, async	=> requeue
> - *	dirty, sync	=> flush, wait and reclaim
> + * We do no IO here - if callers require indoes to be cleaned they must push the

"...require inodes to be cleaned..."

> + * AIL first to trigger writeback of dirty inodes. The enbales both the

"This enables writeback to be done in the background in a non-blocking
manner, and enables memory reclaim to make progress without blocking."

--D

> + * writeback to be done in the background in a non-blocking manner, as well as
> + * allowing reclaim to make progress without blocking.
>   */
>  static bool
>  xfs_reclaim_inode(
> @@ -1327,13 +1271,11 @@ xfs_reclaim_inodes(
>  }
>  
>  /*
> - * Scan a certain number of inodes for reclaim.
> - *
> - * When called we make sure that there is a background (fast) inode reclaim in
> - * progress, while we will throttle the speed of reclaim via doing synchronous
> - * reclaim of inodes. That means if we come across dirty inodes, we wait for
> - * them to be cleaned, which we hope will not be very long due to the
> - * background walker having already kicked the IO off on those dirty inodes.
> + * The shrinker infrastructure determines how many inodes we should scan for
> + * reclaim. We want as many clean inodes ready to reclaim as possible, so we
> + * push the AIL here. We also want to proactively free up memory if we can to
> + * minimise the amount of work memory reclaim has to do so we kick the
> + * background reclaim if it isn't already scheduled.
>   */
>  long
>  xfs_reclaim_inodes_nr(
> -- 
> 2.26.2.761.g0e0b3e54be
> 

  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
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 [this message]
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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