[PATCH v3 0/8] repair: Phase 6 performance improvements

[PATCH v3 0/8] repair: Phase 6 performance improvements

[Gao Xiang]

From: Gao Xiang <hsiangkao@redhat.com>

Hi folks,

This version addresses comments except for some points I mentioned in
https://lore.kernel.org/r/20210324012655.GA2245176@xiangao.remote.csb

since I don't have such test setting, I just ran fstests and it
seems fine.. Hopefully of some help to this patchset and I don't
miss something.

Changelog since v2:
 - support multiple producers suggested by Darrick;
 - turn bad inode list into array, although no bulk allocation yet,
   and not sure if it'd help (Christoph);
 - use namebuf[] instead of pointer arithmetics (Christoph);

Original description:

Phase 6 is single threaded, processing a single AG at a time and a
single directory inode at a time.  Phase 6 if often IO latency bound
despite the prefetching it does, resulting in low disk utilisation
and high runtimes. The solution for this is the same as phase 3 and
4 - scan multiple AGs at once for directory inodes to process. This
patch set enables phase 6 to scan multiple AGS at once, and hence
requires concurrent updates of inode records as tehy can be accessed
and modified by multiple scanning threads now. We also need to
protect the bad inodes list from concurrent access and then we can
enable concurrent processing of directories.

However, directory entry checking and reconstruction can also be CPU
bound - large directories overwhelm the directory name hash
structures because the algorithms have poor scalability - one is O(n
+ n^2), another is O(n^2) when the number of dirents greatly
outsizes the hash table sizes. Hence we need to more than just
parallelise across AGs - we need to parallelise processing within
AGs so that a single large directory doesn't completely serialise
processing within an AG.  This is done by using bound-depth
workqueues to allow inode records to be processed asynchronously as
the inode records are fetched from disk.

Further, we need to fix the bad alogrithmic scalability of the in
memory directory tracking structures. This is done through a
combination of better structures and more appropriate dynamic size
choices.

The results on a filesystem with a single 10 million entry directory
containing 400MB of directory entry data is as follows:

v5.6.0 (Baseline)

       XFS_REPAIR Summary    Thu Oct 22 12:10:52 2020

Phase           Start           End             Duration
Phase 1:        10/22 12:06:41  10/22 12:06:41
Phase 2:        10/22 12:06:41  10/22 12:06:41
Phase 3:        10/22 12:06:41  10/22 12:07:00  19 seconds
Phase 4:        10/22 12:07:00  10/22 12:07:12  12 seconds
Phase 5:        10/22 12:07:12  10/22 12:07:13  1 second
Phase 6:        10/22 12:07:13  10/22 12:10:51  3 minutes, 38 seconds
Phase 7:        10/22 12:10:51  10/22 12:10:51

Total run time: 4 minutes, 10 seconds

real	4m11.151s
user	4m20.083s
sys	0m14.744s


5.9.0-rc1 + patchset:

        XFS_REPAIR Summary    Thu Oct 22 13:19:02 2020

Phase           Start           End             Duration
Phase 1:        10/22 13:18:09  10/22 13:18:09
Phase 2:        10/22 13:18:09  10/22 13:18:09
Phase 3:        10/22 13:18:09  10/22 13:18:31  22 seconds
Phase 4:        10/22 13:18:31  10/22 13:18:45  14 seconds
Phase 5:        10/22 13:18:45  10/22 13:18:45
Phase 6:        10/22 13:18:45  10/22 13:19:00  15 seconds
Phase 7:        10/22 13:19:00  10/22 13:19:00

Total run time: 51 seconds

real	0m52.375s
user	1m3.739s
sys	0m20.346s


Performance improvements on filesystems with small directories and
really fast storage are, at best, modest. The big improvements are
seen with either really large directories and/or relatively slow
devices that are IO latency bound and can benefit from having more
IO in flight at once.

Thanks,
Gao Xiang

Dave Chinner (7):
  workqueue: bound maximum queue depth
  repair: Protect bad inode list with mutex
  repair: protect inode chunk tree records with a mutex
  repair: parallelise phase 6
  repair: don't duplicate names in phase 6
  repair: convert the dir byaddr hash to a radix tree
  repair: scale duplicate name checking in phase 6.

Gao Xiang (1):
  repair: turn bad inode list into array

 libfrog/radix-tree.c |  46 +++++
 libfrog/workqueue.c  |  42 ++++-
 libfrog/workqueue.h  |   4 +
 repair/dir2.c        |  43 +++--
 repair/dir2.h        |   2 +-
 repair/incore.h      |  23 +++
 repair/incore_ino.c  |  15 ++
 repair/phase6.c      | 395 +++++++++++++++++++++----------------------
 8 files changed, 343 insertions(+), 227 deletions(-)

-- 
2.20.1

[PATCH v3 1/8] repair: turn bad inode list into array

[Gao Xiang]

From: Gao Xiang <hsiangkao@redhat.com>

Just use array and reallocate one-by-one here (not sure if bulk
allocation is more effective or not.)

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 repair/dir2.c | 34 +++++++++++++++++-----------------
 repair/dir2.h |  2 +-
 2 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/repair/dir2.c b/repair/dir2.c
index eabdb4f2d497..b6a8a5c40ae4 100644
--- a/repair/dir2.c
+++ b/repair/dir2.c
@@ -20,40 +20,40 @@
  * Known bad inode list.  These are seen when the leaf and node
  * block linkages are incorrect.
  */
-typedef struct dir2_bad {
-	xfs_ino_t	ino;
-	struct dir2_bad	*next;
-} dir2_bad_t;
+struct dir2_bad {
+	unsigned int	nr;
+	xfs_ino_t	*itab;
+};
 
-static dir2_bad_t *dir2_bad_list;
+static struct dir2_bad	dir2_bad;
 
 static void
 dir2_add_badlist(
 	xfs_ino_t	ino)
 {
-	dir2_bad_t	*l;
+	xfs_ino_t	*itab;
 
-	if ((l = malloc(sizeof(dir2_bad_t))) == NULL) {
+	itab = realloc(dir2_bad.itab, (dir2_bad.nr + 1) * sizeof(xfs_ino_t));
+	if (!itab) {
 		do_error(
 _("malloc failed (%zu bytes) dir2_add_badlist:ino %" PRIu64 "\n"),
-			sizeof(dir2_bad_t), ino);
+			sizeof(xfs_ino_t), ino);
 		exit(1);
 	}
-	l->next = dir2_bad_list;
-	dir2_bad_list = l;
-	l->ino = ino;
+	itab[dir2_bad.nr++] = ino;
+	dir2_bad.itab = itab;
 }
 
-int
+bool
 dir2_is_badino(
 	xfs_ino_t	ino)
 {
-	dir2_bad_t	*l;
+	unsigned int i;
 
-	for (l = dir2_bad_list; l; l = l->next)
-		if (l->ino == ino)
-			return 1;
-	return 0;
+	for (i = 0; i < dir2_bad.nr; ++i)
+		if (dir2_bad.itab[i] == ino)
+			return true;
+	return false;
 }
 
 /*
diff --git a/repair/dir2.h b/repair/dir2.h
index 5795aac5eaab..af4cfb1da329 100644
--- a/repair/dir2.h
+++ b/repair/dir2.h
@@ -27,7 +27,7 @@ process_sf_dir2_fixi8(
 	struct xfs_dir2_sf_hdr	*sfp,
 	xfs_dir2_sf_entry_t	**next_sfep);
 
-int
+bool
 dir2_is_badino(
 	xfs_ino_t	ino);
 
-- 
2.20.1

Re: [PATCH v3 1/8] repair: turn bad inode list into array

[Darrick J. Wong]

On Tue, Mar 30, 2021 at 10:25:24PM +0800, Gao Xiang wrote:
> From: Gao Xiang <hsiangkao@redhat.com>
> 
> Just use array and reallocate one-by-one here (not sure if bulk
> allocation is more effective or not.)

I'm not sure either.  The list of bad directories is likely to be
sparse, so perhaps the libfrog bitmap isn't going to beat a realloc
array for space efficiency... and reusing the slab array might be
overkill for an array-backed bitmap?

Eh, you know what?  I don't think the bad directory bitmap is hot enough
to justify broadening this into an algorithmic review of data
structures.  Incremental space efficiency is good enough for me.

> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> ---
>  repair/dir2.c | 34 +++++++++++++++++-----------------
>  repair/dir2.h |  2 +-
>  2 files changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/repair/dir2.c b/repair/dir2.c
> index eabdb4f2d497..b6a8a5c40ae4 100644
> --- a/repair/dir2.c
> +++ b/repair/dir2.c
> @@ -20,40 +20,40 @@
>   * Known bad inode list.  These are seen when the leaf and node
>   * block linkages are incorrect.
>   */
> -typedef struct dir2_bad {
> -	xfs_ino_t	ino;
> -	struct dir2_bad	*next;
> -} dir2_bad_t;
> +struct dir2_bad {
> +	unsigned int	nr;

We could have more than 4 billion bad directories.

> +	xfs_ino_t	*itab;
> +};
>  
> -static dir2_bad_t *dir2_bad_list;
> +static struct dir2_bad	dir2_bad;
>  
>  static void
>  dir2_add_badlist(
>  	xfs_ino_t	ino)
>  {
> -	dir2_bad_t	*l;
> +	xfs_ino_t	*itab;
>  
> -	if ((l = malloc(sizeof(dir2_bad_t))) == NULL) {
> +	itab = realloc(dir2_bad.itab, (dir2_bad.nr + 1) * sizeof(xfs_ino_t));

Minor quibble: you could improve the efficiency of this by tracking both
the array size and fill count so that you only have to expand the array
by powers of two at a time.  The glibc heap is faster than it once was,
but you could help it along by only asking for memory in MMAP_THRESHOLD
chunks.  Or possibly even pagesize chunks.

--D

> +	if (!itab) {
>  		do_error(
>  _("malloc failed (%zu bytes) dir2_add_badlist:ino %" PRIu64 "\n"),
> -			sizeof(dir2_bad_t), ino);
> +			sizeof(xfs_ino_t), ino);
>  		exit(1);
>  	}
> -	l->next = dir2_bad_list;
> -	dir2_bad_list = l;
> -	l->ino = ino;
> +	itab[dir2_bad.nr++] = ino;
> +	dir2_bad.itab = itab;
>  }
>  
> -int
> +bool
>  dir2_is_badino(
>  	xfs_ino_t	ino)
>  {
> -	dir2_bad_t	*l;
> +	unsigned int i;
>  
> -	for (l = dir2_bad_list; l; l = l->next)
> -		if (l->ino == ino)
> -			return 1;
> -	return 0;
> +	for (i = 0; i < dir2_bad.nr; ++i)
> +		if (dir2_bad.itab[i] == ino)
> +			return true;
> +	return false;
>  }
>  
>  /*
> diff --git a/repair/dir2.h b/repair/dir2.h
> index 5795aac5eaab..af4cfb1da329 100644
> --- a/repair/dir2.h
> +++ b/repair/dir2.h
> @@ -27,7 +27,7 @@ process_sf_dir2_fixi8(
>  	struct xfs_dir2_sf_hdr	*sfp,
>  	xfs_dir2_sf_entry_t	**next_sfep);
>  
> -int
> +bool
>  dir2_is_badino(
>  	xfs_ino_t	ino);
>  
> -- 
> 2.20.1
> 

Re: [PATCH v3 1/8] repair: turn bad inode list into array

[Gao Xiang]

Hi Darrick,

On Tue, Mar 30, 2021 at 11:46:08AM -0700, Darrick J. Wong wrote:
> On Tue, Mar 30, 2021 at 10:25:24PM +0800, Gao Xiang wrote:
> > From: Gao Xiang <hsiangkao@redhat.com>
> > 
> > Just use array and reallocate one-by-one here (not sure if bulk
> > allocation is more effective or not.)
> 
> I'm not sure either.  The list of bad directories is likely to be
> sparse, so perhaps the libfrog bitmap isn't going to beat a realloc
> array for space efficiency... and reusing the slab array might be
> overkill for an array-backed bitmap?
> 
> Eh, you know what?  I don't think the bad directory bitmap is hot enough
> to justify broadening this into an algorithmic review of data
> structures.  Incremental space efficiency is good enough for me.

I'm not sure if it's a good choice tbh, let me try to use some
balanced binary tree instead as Dave suggested.

Thanks,
Gao Xiang

Re: [PATCH v3 1/8] repair: turn bad inode list into array

[Dave Chinner]

On Tue, Mar 30, 2021 at 10:25:24PM +0800, Gao Xiang wrote:
> From: Gao Xiang <hsiangkao@redhat.com>
> 
> Just use array and reallocate one-by-one here (not sure if bulk
> allocation is more effective or not.)

Did you profile repairing a filesystem with lots of broken
directories? Optimisations like this really need to be profile
guided and the impact docuemnted. That way reviewers can actually
see the benefit the change brings to the table....

> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> ---
>  repair/dir2.c | 34 +++++++++++++++++-----------------
>  repair/dir2.h |  2 +-
>  2 files changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/repair/dir2.c b/repair/dir2.c
> index eabdb4f2d497..b6a8a5c40ae4 100644
> --- a/repair/dir2.c
> +++ b/repair/dir2.c
> @@ -20,40 +20,40 @@
>   * Known bad inode list.  These are seen when the leaf and node
>   * block linkages are incorrect.
>   */
> -typedef struct dir2_bad {
> -	xfs_ino_t	ino;
> -	struct dir2_bad	*next;
> -} dir2_bad_t;
> +struct dir2_bad {
> +	unsigned int	nr;
> +	xfs_ino_t	*itab;
> +};
>  
> -static dir2_bad_t *dir2_bad_list;
> +static struct dir2_bad	dir2_bad;
>  
>  static void
>  dir2_add_badlist(
>  	xfs_ino_t	ino)
>  {
> -	dir2_bad_t	*l;
> +	xfs_ino_t	*itab;
>  
> -	if ((l = malloc(sizeof(dir2_bad_t))) == NULL) {
> +	itab = realloc(dir2_bad.itab, (dir2_bad.nr + 1) * sizeof(xfs_ino_t));
> +	if (!itab) {
>  		do_error(
>  _("malloc failed (%zu bytes) dir2_add_badlist:ino %" PRIu64 "\n"),
> -			sizeof(dir2_bad_t), ino);
> +			sizeof(xfs_ino_t), ino);
>  		exit(1);
>  	}
> -	l->next = dir2_bad_list;
> -	dir2_bad_list = l;
> -	l->ino = ino;
> +	itab[dir2_bad.nr++] = ino;
> +	dir2_bad.itab = itab;
>  }
>  
> -int
> +bool
>  dir2_is_badino(
>  	xfs_ino_t	ino)
>  {
> -	dir2_bad_t	*l;
> +	unsigned int i;
>  
> -	for (l = dir2_bad_list; l; l = l->next)
> -		if (l->ino == ino)
> -			return 1;
> -	return 0;
> +	for (i = 0; i < dir2_bad.nr; ++i)
> +		if (dir2_bad.itab[i] == ino)
> +			return true;
> +	return false;

This ignores the problem with this code: it is a O(n * N) search
that gets done under an exclusive lock. Changing this to an array
doesn't improve the efficiency of the algorithm at all. It might
slighty reduce the magnitude of N, but modern CPU prefetchers detect
link list walks like this so are almost as fast sequentail array
walks. Hence this change will gain us relatively little when we have
millions of bad inodes to search.

IOWs, the scalability problem that needs to be solved here is not
"replace a linked list", it is "replace an O(n * N) search
algorithm". We should address the algorithmic problem, not the code
implementation issue.

That means we need to replace the linear search with a different
algorithm, not rework the data structure used to do a linear search.
We want this search to be reduced to O(n * log N) or O(n). We really
don't care about memory usage or even the overhead of per-object
memory allocation - we already do that and it isn't a performance
limitation, so optimising for memory allocation reductions is
optimising the wrong thing.

Replacing the linked list with an AVL tree or radix tree will make
the search O(log N), giving us the desired reduction in search
overhead to O(n * log N) and, more importantly, a significant
reduction in lock hold times.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

Re: [PATCH v3 1/8] repair: turn bad inode list into array

[Gao Xiang]

On Wed, Mar 31, 2021 at 09:18:58AM +1100, Dave Chinner wrote:
> On Tue, Mar 30, 2021 at 10:25:24PM +0800, Gao Xiang wrote:
> > From: Gao Xiang <hsiangkao@redhat.com>
> > 
> > Just use array and reallocate one-by-one here (not sure if bulk
> > allocation is more effective or not.)
> 
> Did you profile repairing a filesystem with lots of broken
> directories? Optimisations like this really need to be profile
> guided and the impact docuemnted. That way reviewers can actually
> see the benefit the change brings to the table....

Nope, will do then (since I'm not confident with the target
performance tbh.)

> 
> > Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> > ---
> >  repair/dir2.c | 34 +++++++++++++++++-----------------
> >  repair/dir2.h |  2 +-
> >  2 files changed, 18 insertions(+), 18 deletions(-)
> > 
> > diff --git a/repair/dir2.c b/repair/dir2.c
> > index eabdb4f2d497..b6a8a5c40ae4 100644
> > --- a/repair/dir2.c
> > +++ b/repair/dir2.c
> > @@ -20,40 +20,40 @@
> >   * Known bad inode list.  These are seen when the leaf and node
> >   * block linkages are incorrect.
> >   */
> > -typedef struct dir2_bad {
> > -	xfs_ino_t	ino;
> > -	struct dir2_bad	*next;
> > -} dir2_bad_t;
> > +struct dir2_bad {
> > +	unsigned int	nr;
> > +	xfs_ino_t	*itab;
> > +};
> >  
> > -static dir2_bad_t *dir2_bad_list;
> > +static struct dir2_bad	dir2_bad;
> >  
> >  static void
> >  dir2_add_badlist(
> >  	xfs_ino_t	ino)
> >  {
> > -	dir2_bad_t	*l;
> > +	xfs_ino_t	*itab;
> >  
> > -	if ((l = malloc(sizeof(dir2_bad_t))) == NULL) {
> > +	itab = realloc(dir2_bad.itab, (dir2_bad.nr + 1) * sizeof(xfs_ino_t));
> > +	if (!itab) {
> >  		do_error(
> >  _("malloc failed (%zu bytes) dir2_add_badlist:ino %" PRIu64 "\n"),
> > -			sizeof(dir2_bad_t), ino);
> > +			sizeof(xfs_ino_t), ino);
> >  		exit(1);
> >  	}
> > -	l->next = dir2_bad_list;
> > -	dir2_bad_list = l;
> > -	l->ino = ino;
> > +	itab[dir2_bad.nr++] = ino;
> > +	dir2_bad.itab = itab;
> >  }
> >  
> > -int
> > +bool
> >  dir2_is_badino(
> >  	xfs_ino_t	ino)
> >  {
> > -	dir2_bad_t	*l;
> > +	unsigned int i;
> >  
> > -	for (l = dir2_bad_list; l; l = l->next)
> > -		if (l->ino == ino)
> > -			return 1;
> > -	return 0;
> > +	for (i = 0; i < dir2_bad.nr; ++i)
> > +		if (dir2_bad.itab[i] == ino)
> > +			return true;
> > +	return false;
> 
> This ignores the problem with this code: it is a O(n * N) search
> that gets done under an exclusive lock. Changing this to an array
> doesn't improve the efficiency of the algorithm at all. It might
> slighty reduce the magnitude of N, but modern CPU prefetchers detect
> link list walks like this so are almost as fast sequentail array
> walks. Hence this change will gain us relatively little when we have
> millions of bad inodes to search.
> 
> IOWs, the scalability problem that needs to be solved here is not
> "replace a linked list", it is "replace an O(n * N) search
> algorithm". We should address the algorithmic problem, not the code
> implementation issue.
> 
> That means we need to replace the linear search with a different
> algorithm, not rework the data structure used to do a linear search.
> We want this search to be reduced to O(n * log N) or O(n). We really
> don't care about memory usage or even the overhead of per-object
> memory allocation - we already do that and it isn't a performance
> limitation, so optimising for memory allocation reductions is
> optimising the wrong thing.
> 
> Replacing the linked list with an AVL tree or radix tree will make
> the search O(log N), giving us the desired reduction in search
> overhead to O(n * log N) and, more importantly, a significant
> reduction in lock hold times.

Obviously, I agree with your idea. Radix tree indexed by inode number
may waste space. I didn't notice that repair code had some AVL
infrastructure, let me try to use AVL instead.

But anyway, I'm not sure if it's a critical problem and if users really
came into bad inode bomb. Use array here just because some previous
review suggestion.

Thanks,
Gao Xiang

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

[PATCH v3 2/8] workqueue: bound maximum queue depth

[Gao Xiang]

From: Dave Chinner <dchinner@redhat.com>

Existing users of workqueues have bound maximum queue depths in
their external algorithms (e.g. prefetch counts). For parallelising
work that doesn't have an external bound, allow workqueues to
throttle incoming requests at a maximum bound. Bounded workqueues
also need to distribute work over all worker threads themselves as
there is no external bounding or worker function throttling
provided.

Existing callers are not throttled and retain direct control of
worker threads, only users of the new create interface will be
throttled and concurrency managed.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 libfrog/workqueue.c | 42 +++++++++++++++++++++++++++++++++++++++---
 libfrog/workqueue.h |  4 ++++
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/libfrog/workqueue.c b/libfrog/workqueue.c
index fe3de4289379..8c1a163e145f 100644
--- a/libfrog/workqueue.c
+++ b/libfrog/workqueue.c
@@ -40,13 +40,21 @@ workqueue_thread(void *arg)
 		}
 
 		/*
-		 *  Dequeue work from the head of the list.
+		 *  Dequeue work from the head of the list. If the queue was
+		 *  full then send a wakeup if we're configured to do so.
 		 */
 		assert(wq->item_count > 0);
+		if (wq->max_queued)
+			pthread_cond_broadcast(&wq->queue_full);
+
 		wi = wq->next_item;
 		wq->next_item = wi->next;
 		wq->item_count--;
 
+		if (wq->max_queued && wq->next_item) {
+			/* more work, wake up another worker */
+			pthread_cond_signal(&wq->wakeup);
+		}
 		pthread_mutex_unlock(&wq->lock);
 
 		(wi->function)(wi->queue, wi->index, wi->arg);
@@ -58,10 +66,11 @@ workqueue_thread(void *arg)
 
 /* Allocate a work queue and threads.  Returns zero or negative error code. */
 int
-workqueue_create(
+workqueue_create_bound(
 	struct workqueue	*wq,
 	void			*wq_ctx,
-	unsigned int		nr_workers)
+	unsigned int		nr_workers,
+	unsigned int		max_queue)
 {
 	unsigned int		i;
 	int			err = 0;
@@ -70,12 +79,16 @@ workqueue_create(
 	err = -pthread_cond_init(&wq->wakeup, NULL);
 	if (err)
 		return err;
+	err = -pthread_cond_init(&wq->queue_full, NULL);
+	if (err)
+		goto out_wake;
 	err = -pthread_mutex_init(&wq->lock, NULL);
 	if (err)
 		goto out_cond;
 
 	wq->wq_ctx = wq_ctx;
 	wq->thread_count = nr_workers;
+	wq->max_queued = max_queue;
 	wq->threads = malloc(nr_workers * sizeof(pthread_t));
 	if (!wq->threads) {
 		err = -errno;
@@ -102,10 +115,21 @@ workqueue_create(
 out_mutex:
 	pthread_mutex_destroy(&wq->lock);
 out_cond:
+	pthread_cond_destroy(&wq->queue_full);
+out_wake:
 	pthread_cond_destroy(&wq->wakeup);
 	return err;
 }
 
+int
+workqueue_create(
+	struct workqueue	*wq,
+	void			*wq_ctx,
+	unsigned int		nr_workers)
+{
+	return workqueue_create_bound(wq, wq_ctx, nr_workers, 0);
+}
+
 /*
  * Create a work item consisting of a function and some arguments and schedule
  * the work item to be run via the thread pool.  Returns zero or a negative
@@ -140,6 +164,7 @@ workqueue_add(
 
 	/* Now queue the new work structure to the work queue. */
 	pthread_mutex_lock(&wq->lock);
+restart:
 	if (wq->next_item == NULL) {
 		assert(wq->item_count == 0);
 		ret = -pthread_cond_signal(&wq->wakeup);
@@ -150,6 +175,16 @@ workqueue_add(
 		}
 		wq->next_item = wi;
 	} else {
+		/* throttle on a full queue if configured */
+		if (wq->max_queued && wq->item_count == wq->max_queued) {
+			pthread_cond_wait(&wq->queue_full, &wq->lock);
+			/*
+			 * Queue might be empty or even still full by the time
+			 * we get the lock back, so restart the lookup so we do
+			 * the right thing with the current state of the queue.
+			 */
+			goto restart;
+		}
 		wq->last_item->next = wi;
 	}
 	wq->last_item = wi;
@@ -201,5 +236,6 @@ workqueue_destroy(
 	free(wq->threads);
 	pthread_mutex_destroy(&wq->lock);
 	pthread_cond_destroy(&wq->wakeup);
+	pthread_cond_destroy(&wq->queue_full);
 	memset(wq, 0, sizeof(*wq));
 }
diff --git a/libfrog/workqueue.h b/libfrog/workqueue.h
index a56d1cf14081..a9c108d0e66a 100644
--- a/libfrog/workqueue.h
+++ b/libfrog/workqueue.h
@@ -31,10 +31,14 @@ struct workqueue {
 	unsigned int		thread_count;
 	bool			terminate;
 	bool			terminated;
+	int			max_queued;
+	pthread_cond_t		queue_full;
 };
 
 int workqueue_create(struct workqueue *wq, void *wq_ctx,
 		unsigned int nr_workers);
+int workqueue_create_bound(struct workqueue *wq, void *wq_ctx,
+		unsigned int nr_workers, unsigned int max_queue);
 int workqueue_add(struct workqueue *wq, workqueue_func_t fn,
 		uint32_t index, void *arg);
 int workqueue_terminate(struct workqueue *wq);
-- 
2.20.1

[PATCH v3 3/8] repair: Protect bad inode list with mutex

[Gao Xiang]

From: Dave Chinner <dchinner@redhat.com>

To enable phase 6 parallelisation, we need to protect the bad inode
list from concurrent modification and/or access. Wrap it with a
mutex and clean up the nasty typedefs.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 repair/dir2.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/repair/dir2.c b/repair/dir2.c
index b6a8a5c40ae4..c1d262fb1207 100644
--- a/repair/dir2.c
+++ b/repair/dir2.c
@@ -26,6 +26,7 @@ struct dir2_bad {
 };
 
 static struct dir2_bad	dir2_bad;
+pthread_mutex_t		dir2_bad_lock = PTHREAD_MUTEX_INITIALIZER;
 
 static void
 dir2_add_badlist(
@@ -33,6 +34,7 @@ dir2_add_badlist(
 {
 	xfs_ino_t	*itab;
 
+	pthread_mutex_lock(&dir2_bad_lock);
 	itab = realloc(dir2_bad.itab, (dir2_bad.nr + 1) * sizeof(xfs_ino_t));
 	if (!ino) {
 		do_error(
@@ -42,18 +44,25 @@ _("malloc failed (%zu bytes) dir2_add_badlist:ino %" PRIu64 "\n"),
 	}
 	itab[dir2_bad.nr++] = ino;
 	dir2_bad.itab = itab;
+	pthread_mutex_unlock(&dir2_bad_lock);
 }
 
 bool
 dir2_is_badino(
 	xfs_ino_t	ino)
 {
-	unsigned int i;
+	unsigned int	i;
+	bool		ret = false;
 
-	for (i = 0; i < dir2_bad.nr; ++i)
-		if (dir2_bad.itab[i] == ino)
-			return true;
-	return false;
+	pthread_mutex_lock(&dir2_bad_lock);
+	for (i = 0; i < dir2_bad.nr; ++i) {
+		if (dir2_bad.itab[i] == ino) {
+			ret = true;
+			break;
+		}
+	}
+	pthread_mutex_unlock(&dir2_bad_lock);
+	return ret;
 }
 
 /*
-- 
2.20.1

[PATCH v3 RESEND 3/8] repair: Protect bad inode list with mutex

[Gao Xiang]

From: Dave Chinner <dchinner@redhat.com>

To enable phase 6 parallelisation, we need to protect the bad inode
list from concurrent modification and/or access. Wrap it with a
mutex and clean up the nasty typedefs.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
RESEND:
 - fix broken v3 due to rebasing

 repair/dir2.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/repair/dir2.c b/repair/dir2.c
index b6a8a5c40ae4..c1d262fb1207 100644
--- a/repair/dir2.c
+++ b/repair/dir2.c
@@ -26,6 +26,7 @@ struct dir2_bad {
 };
 
 static struct dir2_bad	dir2_bad;
+pthread_mutex_t		dir2_bad_lock = PTHREAD_MUTEX_INITIALIZER;
 
 static void
 dir2_add_badlist(
@@ -33,6 +34,7 @@ dir2_add_badlist(
 {
 	xfs_ino_t	*itab;
 
+	pthread_mutex_lock(&dir2_bad_lock);
 	itab = realloc(dir2_bad.itab, (dir2_bad.nr + 1) * sizeof(xfs_ino_t));
 	if (!itab) {
 		do_error(
@@ -42,18 +44,25 @@ _("malloc failed (%zu bytes) dir2_add_badlist:ino %" PRIu64 "\n"),
 	}
 	itab[dir2_bad.nr++] = ino;
 	dir2_bad.itab = itab;
+	pthread_mutex_unlock(&dir2_bad_lock);
 }
 
 bool
 dir2_is_badino(
 	xfs_ino_t	ino)
 {
-	unsigned int i;
+	unsigned int	i;
+	bool		ret = false;
 
-	for (i = 0; i < dir2_bad.nr; ++i)
-		if (dir2_bad.itab[i] == ino)
-			return true;
-	return false;
+	pthread_mutex_lock(&dir2_bad_lock);
+	for (i = 0; i < dir2_bad.nr; ++i) {
+		if (dir2_bad.itab[i] == ino) {
+			ret = true;
+			break;
+		}
+	}
+	pthread_mutex_unlock(&dir2_bad_lock);
+	return ret;
 }
 
 /*
-- 
2.20.1

Re: [PATCH v3 3/8] repair: Protect bad inode list with mutex

[Dave Chinner]

On Tue, Mar 30, 2021 at 10:25:26PM +0800, Gao Xiang wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> To enable phase 6 parallelisation, we need to protect the bad inode
> list from concurrent modification and/or access. Wrap it with a
> mutex and clean up the nasty typedefs.
> 
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> ---
>  repair/dir2.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/repair/dir2.c b/repair/dir2.c
> index b6a8a5c40ae4..c1d262fb1207 100644
> --- a/repair/dir2.c
> +++ b/repair/dir2.c
> @@ -26,6 +26,7 @@ struct dir2_bad {
>  };
>  
>  static struct dir2_bad	dir2_bad;
> +pthread_mutex_t		dir2_bad_lock = PTHREAD_MUTEX_INITIALIZER;
>  
>  static void
>  dir2_add_badlist(
> @@ -33,6 +34,7 @@ dir2_add_badlist(
>  {
>  	xfs_ino_t	*itab;
>  
> +	pthread_mutex_lock(&dir2_bad_lock);
>  	itab = realloc(dir2_bad.itab, (dir2_bad.nr + 1) * sizeof(xfs_ino_t));
>  	if (!ino) {
>  		do_error(
> @@ -42,18 +44,25 @@ _("malloc failed (%zu bytes) dir2_add_badlist:ino %" PRIu64 "\n"),
>  	}
>  	itab[dir2_bad.nr++] = ino;
>  	dir2_bad.itab = itab;
> +	pthread_mutex_unlock(&dir2_bad_lock);

Putting a global mutex around a memory allocation like this will
really hurt concurrency. This turns the add operation into a very
complex operation instead of the critical section being just a few
instructions long.

The existing linked list code is far more efficient in this case
because the allocation of the structure tracking the bad inode is
done outside the global lock, and only the list_add() operation is
done within the critical section.

Again, an AVL or radix tree can do the tracking structure allocation
outside the add operation, and with an AVL tree there are no
allocations needed to do the insert operation. A radix tree will
amortise the allocations its needs over many inserts that don't need
allocation. However, I'd be tending towards using an AVL tree here
over a radix tree because bad inodes will be sparse and that's the
worst case for radix tree indexing w.r.t to requiring allocation
during insert...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

Re: [PATCH v3 3/8] repair: Protect bad inode list with mutex

[Gao Xiang]

On Wed, Mar 31, 2021 at 09:26:42AM +1100, Dave Chinner wrote:
> On Tue, Mar 30, 2021 at 10:25:26PM +0800, Gao Xiang wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > To enable phase 6 parallelisation, we need to protect the bad inode
> > list from concurrent modification and/or access. Wrap it with a
> > mutex and clean up the nasty typedefs.
> > 
> > Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> > ---
> >  repair/dir2.c | 19 ++++++++++++++-----
> >  1 file changed, 14 insertions(+), 5 deletions(-)
> > 
> > diff --git a/repair/dir2.c b/repair/dir2.c
> > index b6a8a5c40ae4..c1d262fb1207 100644
> > --- a/repair/dir2.c
> > +++ b/repair/dir2.c
> > @@ -26,6 +26,7 @@ struct dir2_bad {
> >  };
> >  
> >  static struct dir2_bad	dir2_bad;
> > +pthread_mutex_t		dir2_bad_lock = PTHREAD_MUTEX_INITIALIZER;
> >  
> >  static void
> >  dir2_add_badlist(
> > @@ -33,6 +34,7 @@ dir2_add_badlist(
> >  {
> >  	xfs_ino_t	*itab;
> >  
> > +	pthread_mutex_lock(&dir2_bad_lock);
> >  	itab = realloc(dir2_bad.itab, (dir2_bad.nr + 1) * sizeof(xfs_ino_t));
> >  	if (!ino) {
> >  		do_error(
> > @@ -42,18 +44,25 @@ _("malloc failed (%zu bytes) dir2_add_badlist:ino %" PRIu64 "\n"),
> >  	}
> >  	itab[dir2_bad.nr++] = ino;
> >  	dir2_bad.itab = itab;
> > +	pthread_mutex_unlock(&dir2_bad_lock);
> 
> Putting a global mutex around a memory allocation like this will
> really hurt concurrency. This turns the add operation into a very
> complex operation instead of the critical section being just a few
> instructions long.
> 
> The existing linked list code is far more efficient in this case
> because the allocation of the structure tracking the bad inode is
> done outside the global lock, and only the list_add() operation is
> done within the critical section.

I agree with your conclusion here and actually realized the problem
at that time.

> 
> Again, an AVL or radix tree can do the tracking structure allocation
> outside the add operation, and with an AVL tree there are no
> allocations needed to do the insert operation. A radix tree will
> amortise the allocations its needs over many inserts that don't need
> allocation. However, I'd be tending towards using an AVL tree here
> over a radix tree because bad inodes will be sparse and that's the
> worst case for radix tree indexing w.r.t to requiring allocation
> during insert...

Yeah, I saw some AVL infrastructure, yet AVL needs amortise insert/lookup
O(logn). Anyway, let me try use ACL instead and do some profile.

Thanks,
Gao Xiang

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

[PATCH v3 4/8] repair: protect inode chunk tree records with a mutex

[Gao Xiang]

From: Dave Chinner <dchinner@redhat.com>

Phase 6 accesses inode chunk records mostly in an isolated manner.
However, when it finds a corruption in a directory or there are
multiple hardlinks to an inode, there can be concurrent access
to the inode chunk record to update state.

Hence the inode record itself needs a mutex. This protects all state
changes within the inode chunk record, as well as inode link counts
and chunk references. That allows us to process multiple chunks at
once, providing concurrency within an AG as well as across AGs.

The inode chunk tree itself is not modified in the directory
scanning and rebuilding part of phase 6 which we are making
concurrent, hence we do not need to worry about locking for AVL tree
lookups to find the inode chunk records themselves. Therefore
internal locking is all we need here.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 repair/incore.h     | 23 +++++++++++++++++++++++
 repair/incore_ino.c | 15 +++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/repair/incore.h b/repair/incore.h
index 977e5dd04336..d64315fd2585 100644
--- a/repair/incore.h
+++ b/repair/incore.h
@@ -281,6 +281,7 @@ typedef struct ino_tree_node  {
 		parent_list_t	*plist;		/* phases 2-5 */
 	} ino_un;
 	uint8_t			*ftypes;	/* phases 3,6 */
+	pthread_mutex_t		lock;
 } ino_tree_node_t;
 
 #define INOS_PER_IREC	(sizeof(uint64_t) * NBBY)
@@ -411,7 +412,9 @@ next_free_ino_rec(ino_tree_node_t *ino_rec)
  */
 static inline void add_inode_refchecked(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	irec->ino_un.ex_data->ino_processed |= IREC_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 static inline int is_inode_refchecked(struct ino_tree_node *irec, int offset)
@@ -437,12 +440,16 @@ static inline int is_inode_confirmed(struct ino_tree_node *irec, int offset)
  */
 static inline void set_inode_isadir(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	irec->ino_isa_dir |= IREC_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 static inline void clear_inode_isadir(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	irec->ino_isa_dir &= ~IREC_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 static inline int inode_isadir(struct ino_tree_node *irec, int offset)
@@ -455,15 +462,19 @@ static inline int inode_isadir(struct ino_tree_node *irec, int offset)
  */
 static inline void set_inode_free(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	set_inode_confirmed(irec, offset);
 	irec->ir_free |= XFS_INOBT_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 
 }
 
 static inline void set_inode_used(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	set_inode_confirmed(irec, offset);
 	irec->ir_free &= ~XFS_INOBT_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 static inline int is_inode_free(struct ino_tree_node *irec, int offset)
@@ -476,7 +487,9 @@ static inline int is_inode_free(struct ino_tree_node *irec, int offset)
  */
 static inline void set_inode_sparse(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	irec->ir_sparse |= XFS_INOBT_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 static inline bool is_inode_sparse(struct ino_tree_node *irec, int offset)
@@ -489,12 +502,16 @@ static inline bool is_inode_sparse(struct ino_tree_node *irec, int offset)
  */
 static inline void set_inode_was_rl(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	irec->ino_was_rl |= IREC_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 static inline void clear_inode_was_rl(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	irec->ino_was_rl &= ~IREC_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 static inline int inode_was_rl(struct ino_tree_node *irec, int offset)
@@ -507,12 +524,16 @@ static inline int inode_was_rl(struct ino_tree_node *irec, int offset)
  */
 static inline void set_inode_is_rl(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	irec->ino_is_rl |= IREC_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 static inline void clear_inode_is_rl(struct ino_tree_node *irec, int offset)
 {
+	pthread_mutex_lock(&irec->lock);
 	irec->ino_is_rl &= ~IREC_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 static inline int inode_is_rl(struct ino_tree_node *irec, int offset)
@@ -545,7 +566,9 @@ static inline int is_inode_reached(struct ino_tree_node *irec, int offset)
 static inline void add_inode_reached(struct ino_tree_node *irec, int offset)
 {
 	add_inode_ref(irec, offset);
+	pthread_mutex_lock(&irec->lock);
 	irec->ino_un.ex_data->ino_reached |= IREC_MASK(offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 /*
diff --git a/repair/incore_ino.c b/repair/incore_ino.c
index 82956ae93005..299e4f949e5e 100644
--- a/repair/incore_ino.c
+++ b/repair/incore_ino.c
@@ -91,6 +91,7 @@ void add_inode_ref(struct ino_tree_node *irec, int ino_offset)
 {
 	ASSERT(irec->ino_un.ex_data != NULL);
 
+	pthread_mutex_lock(&irec->lock);
 	switch (irec->nlink_size) {
 	case sizeof(uint8_t):
 		if (irec->ino_un.ex_data->counted_nlinks.un8[ino_offset] < 0xff) {
@@ -112,6 +113,7 @@ void add_inode_ref(struct ino_tree_node *irec, int ino_offset)
 	default:
 		ASSERT(0);
 	}
+	pthread_mutex_unlock(&irec->lock);
 }
 
 void drop_inode_ref(struct ino_tree_node *irec, int ino_offset)
@@ -120,6 +122,7 @@ void drop_inode_ref(struct ino_tree_node *irec, int ino_offset)
 
 	ASSERT(irec->ino_un.ex_data != NULL);
 
+	pthread_mutex_lock(&irec->lock);
 	switch (irec->nlink_size) {
 	case sizeof(uint8_t):
 		ASSERT(irec->ino_un.ex_data->counted_nlinks.un8[ino_offset] > 0);
@@ -139,6 +142,7 @@ void drop_inode_ref(struct ino_tree_node *irec, int ino_offset)
 
 	if (refs == 0)
 		irec->ino_un.ex_data->ino_reached &= ~IREC_MASK(ino_offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 uint32_t num_inode_references(struct ino_tree_node *irec, int ino_offset)
@@ -161,6 +165,7 @@ uint32_t num_inode_references(struct ino_tree_node *irec, int ino_offset)
 void set_inode_disk_nlinks(struct ino_tree_node *irec, int ino_offset,
 		uint32_t nlinks)
 {
+	pthread_mutex_lock(&irec->lock);
 	switch (irec->nlink_size) {
 	case sizeof(uint8_t):
 		if (nlinks < 0xff) {
@@ -182,6 +187,7 @@ void set_inode_disk_nlinks(struct ino_tree_node *irec, int ino_offset,
 	default:
 		ASSERT(0);
 	}
+	pthread_mutex_unlock(&irec->lock);
 }
 
 uint32_t get_inode_disk_nlinks(struct ino_tree_node *irec, int ino_offset)
@@ -253,6 +259,7 @@ alloc_ino_node(
 	irec->nlink_size = sizeof(uint8_t);
 	irec->disk_nlinks.un8 = alloc_nlink_array(irec->nlink_size);
 	irec->ftypes = alloc_ftypes_array(mp);
+	pthread_mutex_init(&irec->lock, NULL);
 	return irec;
 }
 
@@ -294,6 +301,7 @@ free_ino_tree_node(
 	}
 
 	free(irec->ftypes);
+	pthread_mutex_destroy(&irec->lock);
 	free(irec);
 }
 
@@ -600,6 +608,7 @@ set_inode_parent(
 	uint64_t		bitmask;
 	parent_entry_t		*tmp;
 
+	pthread_mutex_lock(&irec->lock);
 	if (full_ino_ex_data)
 		ptbl = irec->ino_un.ex_data->parents;
 	else
@@ -625,6 +634,7 @@ set_inode_parent(
 #endif
 		ptbl->pentries[0] = parent;
 
+		pthread_mutex_unlock(&irec->lock);
 		return;
 	}
 
@@ -642,6 +652,7 @@ set_inode_parent(
 #endif
 		ptbl->pentries[target] = parent;
 
+		pthread_mutex_unlock(&irec->lock);
 		return;
 	}
 
@@ -682,6 +693,7 @@ set_inode_parent(
 #endif
 	ptbl->pentries[target] = parent;
 	ptbl->pmask |= (1ULL << offset);
+	pthread_mutex_unlock(&irec->lock);
 }
 
 xfs_ino_t
@@ -692,6 +704,7 @@ get_inode_parent(ino_tree_node_t *irec, int offset)
 	int		i;
 	int		target;
 
+	pthread_mutex_lock(&irec->lock);
 	if (full_ino_ex_data)
 		ptbl = irec->ino_un.ex_data->parents;
 	else
@@ -709,9 +722,11 @@ get_inode_parent(ino_tree_node_t *irec, int offset)
 #ifdef DEBUG
 		ASSERT(target < ptbl->cnt);
 #endif
+		pthread_mutex_unlock(&irec->lock);
 		return(ptbl->pentries[target]);
 	}
 
+	pthread_mutex_unlock(&irec->lock);
 	return(0LL);
 }
 
-- 
2.20.1

[PATCH v3 5/8] repair: parallelise phase 6

[Gao Xiang]

From: Dave Chinner <dchinner@redhat.com>

A recent metadump provided to us caused repair to take hours in
phase6. It wasn't IO bound - it was fully CPU bound the entire time.
The only way to speed it up is to make phase 6 run multiple
concurrent processing threads.

The obvious way to do this is to spread the concurrency across AGs,
like the other phases, and while this works it is not optimal. When
a processing thread hits a really large directory, it essentially
sits CPU bound until that directory is processed. IF an AG has lots
of large directories, we end up with a really long single threaded
tail that limits concurrency.

Hence we also need to have concurrency /within/ the AG. This is
realtively easy, as the inode chunk records allow for a simple
concurrency mechanism within an AG. We can simply feed each chunk
record to a workqueue, and we get concurrency within the AG for
free. However, this allows prefetch to run way ahead of processing
and this blows out the buffer cache size and can cause OOM.

However, we can use the new workqueue depth limiting to limit the
number of inode chunks queued, and this then backs up the inode
prefetching to it's maximum queue depth. Hence we prevent having the
prefetch code queue the entire AG's inode chunks on the workqueue
blowing out memory by throttling the prefetch consumer.

This takes phase 6 from taking many, many hours down to:

Phase 6:        10/30 21:12:58  10/30 21:40:48  27 minutes, 50 seconds

And burning 20-30 cpus that entire time on my test rig.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 repair/phase6.c | 42 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 34 insertions(+), 8 deletions(-)

diff --git a/repair/phase6.c b/repair/phase6.c
index 14464befa8b6..e51784521d28 100644
--- a/repair/phase6.c
+++ b/repair/phase6.c
@@ -6,6 +6,7 @@
 
 #include "libxfs.h"
 #include "threads.h"
+#include "threads.h"
 #include "prefetch.h"
 #include "avl.h"
 #include "globals.h"
@@ -3105,20 +3106,44 @@ check_for_orphaned_inodes(
 }
 
 static void
-traverse_function(
+do_dir_inode(
 	struct workqueue	*wq,
-	xfs_agnumber_t 		agno,
+	xfs_agnumber_t		agno,
 	void			*arg)
 {
-	ino_tree_node_t 	*irec;
+	struct ino_tree_node	*irec = arg;
 	int			i;
+
+	for (i = 0; i < XFS_INODES_PER_CHUNK; i++)  {
+		if (inode_isadir(irec, i))
+			process_dir_inode(wq->wq_ctx, agno, irec, i);
+	}
+}
+
+static void
+traverse_function(
+	struct workqueue	*wq,
+	xfs_agnumber_t		agno,
+	void			*arg)
+{
+	struct ino_tree_node	*irec;
 	prefetch_args_t		*pf_args = arg;
+	struct workqueue	lwq;
+	struct xfs_mount	*mp = wq->wq_ctx;
 
 	wait_for_inode_prefetch(pf_args);
 
 	if (verbose)
 		do_log(_("        - agno = %d\n"), agno);
 
+	/*
+	 * The more AGs we have in flight at once, the fewer processing threads
+	 * per AG. This means we don't overwhelm the machine with hundreds of
+	 * threads when we start acting on lots of AGs at once. We just want
+	 * enough that we can keep multiple CPUs busy across multiple AGs.
+	 */
+	workqueue_create_bound(&lwq, mp, ag_stride, 1000);
+
 	for (irec = findfirst_inode_rec(agno); irec; irec = next_ino_rec(irec)) {
 		if (irec->ino_isa_dir == 0)
 			continue;
@@ -3126,18 +3151,19 @@ traverse_function(
 		if (pf_args) {
 			sem_post(&pf_args->ra_count);
 #ifdef XR_PF_TRACE
+			{
+			int	i;
 			sem_getvalue(&pf_args->ra_count, &i);
 			pftrace(
 		"processing inode chunk %p in AG %d (sem count = %d)",
 				irec, agno, i);
+			}
 #endif
 		}
 
-		for (i = 0; i < XFS_INODES_PER_CHUNK; i++)  {
-			if (inode_isadir(irec, i))
-				process_dir_inode(wq->wq_ctx, agno, irec, i);
-		}
+		queue_work(&lwq, do_dir_inode, agno, irec);
 	}
+	destroy_work_queue(&lwq);
 	cleanup_inode_prefetch(pf_args);
 }
 
@@ -3165,7 +3191,7 @@ static void
 traverse_ags(
 	struct xfs_mount	*mp)
 {
-	do_inode_prefetch(mp, 0, traverse_function, false, true);
+	do_inode_prefetch(mp, ag_stride, traverse_function, false, true);
 }
 
 void
-- 
2.20.1

Re: [PATCH v3 5/8] repair: parallelise phase 6

[Darrick J. Wong]

On Tue, Mar 30, 2021 at 10:25:28PM +0800, Gao Xiang wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> A recent metadump provided to us caused repair to take hours in
> phase6. It wasn't IO bound - it was fully CPU bound the entire time.
> The only way to speed it up is to make phase 6 run multiple
> concurrent processing threads.
> 
> The obvious way to do this is to spread the concurrency across AGs,
> like the other phases, and while this works it is not optimal. When
> a processing thread hits a really large directory, it essentially
> sits CPU bound until that directory is processed. IF an AG has lots
> of large directories, we end up with a really long single threaded
> tail that limits concurrency.
> 
> Hence we also need to have concurrency /within/ the AG. This is
> realtively easy, as the inode chunk records allow for a simple
> concurrency mechanism within an AG. We can simply feed each chunk
> record to a workqueue, and we get concurrency within the AG for
> free. However, this allows prefetch to run way ahead of processing
> and this blows out the buffer cache size and can cause OOM.
> 
> However, we can use the new workqueue depth limiting to limit the
> number of inode chunks queued, and this then backs up the inode
> prefetching to it's maximum queue depth. Hence we prevent having the
> prefetch code queue the entire AG's inode chunks on the workqueue
> blowing out memory by throttling the prefetch consumer.
> 
> This takes phase 6 from taking many, many hours down to:
> 
> Phase 6:        10/30 21:12:58  10/30 21:40:48  27 minutes, 50 seconds
> 
> And burning 20-30 cpus that entire time on my test rig.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> ---
>  repair/phase6.c | 42 ++++++++++++++++++++++++++++++++++--------
>  1 file changed, 34 insertions(+), 8 deletions(-)
> 
> diff --git a/repair/phase6.c b/repair/phase6.c
> index 14464befa8b6..e51784521d28 100644
> --- a/repair/phase6.c
> +++ b/repair/phase6.c
> @@ -6,6 +6,7 @@
>  
>  #include "libxfs.h"
>  #include "threads.h"
> +#include "threads.h"
>  #include "prefetch.h"
>  #include "avl.h"
>  #include "globals.h"
> @@ -3105,20 +3106,44 @@ check_for_orphaned_inodes(
>  }
>  
>  static void
> -traverse_function(
> +do_dir_inode(
>  	struct workqueue	*wq,
> -	xfs_agnumber_t 		agno,
> +	xfs_agnumber_t		agno,
>  	void			*arg)
>  {
> -	ino_tree_node_t 	*irec;
> +	struct ino_tree_node	*irec = arg;
>  	int			i;
> +
> +	for (i = 0; i < XFS_INODES_PER_CHUNK; i++)  {
> +		if (inode_isadir(irec, i))
> +			process_dir_inode(wq->wq_ctx, agno, irec, i);
> +	}
> +}
> +
> +static void
> +traverse_function(
> +	struct workqueue	*wq,
> +	xfs_agnumber_t		agno,
> +	void			*arg)
> +{
> +	struct ino_tree_node	*irec;
>  	prefetch_args_t		*pf_args = arg;
> +	struct workqueue	lwq;
> +	struct xfs_mount	*mp = wq->wq_ctx;
>  
>  	wait_for_inode_prefetch(pf_args);
>  
>  	if (verbose)
>  		do_log(_("        - agno = %d\n"), agno);
>  
> +	/*
> +	 * The more AGs we have in flight at once, the fewer processing threads
> +	 * per AG. This means we don't overwhelm the machine with hundreds of
> +	 * threads when we start acting on lots of AGs at once. We just want
> +	 * enough that we can keep multiple CPUs busy across multiple AGs.
> +	 */
> +	workqueue_create_bound(&lwq, mp, ag_stride, 1000);

At some point I realized that two reviews ago I mixed up the last two
arguments and thought that we were creating 1000 threads.  We're not,
we're creating ag_stride threads and saying that we want to throttle
queue_work if the queue reaches 1000 directory inodes.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D


> +
>  	for (irec = findfirst_inode_rec(agno); irec; irec = next_ino_rec(irec)) {
>  		if (irec->ino_isa_dir == 0)
>  			continue;
> @@ -3126,18 +3151,19 @@ traverse_function(
>  		if (pf_args) {
>  			sem_post(&pf_args->ra_count);
>  #ifdef XR_PF_TRACE
> +			{
> +			int	i;
>  			sem_getvalue(&pf_args->ra_count, &i);
>  			pftrace(
>  		"processing inode chunk %p in AG %d (sem count = %d)",
>  				irec, agno, i);
> +			}
>  #endif
>  		}
>  
> -		for (i = 0; i < XFS_INODES_PER_CHUNK; i++)  {
> -			if (inode_isadir(irec, i))
> -				process_dir_inode(wq->wq_ctx, agno, irec, i);
> -		}
> +		queue_work(&lwq, do_dir_inode, agno, irec);
>  	}
> +	destroy_work_queue(&lwq);
>  	cleanup_inode_prefetch(pf_args);
>  }
>  
> @@ -3165,7 +3191,7 @@ static void
>  traverse_ags(
>  	struct xfs_mount	*mp)
>  {
> -	do_inode_prefetch(mp, 0, traverse_function, false, true);
> +	do_inode_prefetch(mp, ag_stride, traverse_function, false, true);
>  }
>  
>  void
> -- 
> 2.20.1
> 

[PATCH v3 6/8] repair: don't duplicate names in phase 6

[Gao Xiang]

From: Dave Chinner <dchinner@redhat.com>

The name hash in phase 6 is constructed by using names that point
directly into the directory buffers. Hence before the buffers can be
released, the constructed name hash has to duplicate all those names
into meory it owns via dir_hash_dup_names().

Given that the structure that holds the name is dynamically
allocated, it makes no sense to store a pointer to the name
dir_hash_add() and then later have dynamically allocate the name.

Extend the name hash allocation to contain space for the name
itself, and copy the name into the name hash structure in
dir_hash_add(). This allows us to get rid of dir_hash_dup_names(),
and the directory checking code no longer needs to hold all the
directory buffers in memory until the entire directory walk is
complete and the names duplicated.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 repair/phase6.c | 101 ++++++++++++++----------------------------------
 1 file changed, 29 insertions(+), 72 deletions(-)

diff --git a/repair/phase6.c b/repair/phase6.c
index e51784521d28..df8db146c187 100644
--- a/repair/phase6.c
+++ b/repair/phase6.c
@@ -72,15 +72,15 @@ typedef struct dir_hash_ent {
 	struct dir_hash_ent	*nextbyorder;	/* next in order added */
 	xfs_dahash_t		hashval;	/* hash value of name */
 	uint32_t		address;	/* offset of data entry */
-	xfs_ino_t 		inum;		/* inode num of entry */
+	xfs_ino_t		inum;		/* inode num of entry */
 	short			junkit;		/* name starts with / */
 	short			seen;		/* have seen leaf entry */
 	struct xfs_name		name;
+	unsigned char		namebuf[];
 } dir_hash_ent_t;
 
 typedef struct dir_hash_tab {
 	int			size;		/* size of hash tables */
-	int			names_duped;	/* 1 = ent names malloced */
 	dir_hash_ent_t		*first;		/* ptr to first added entry */
 	dir_hash_ent_t		*last;		/* ptr to last added entry */
 	dir_hash_ent_t		**byhash;	/* ptr to name hash buckets */
@@ -171,8 +171,6 @@ dir_hash_add(
 	short			junk;
 	struct xfs_name		xname;
 
-	ASSERT(!hashtab->names_duped);
-
 	xname.name = name;
 	xname.len = namelen;
 	xname.type = ftype;
@@ -199,7 +197,12 @@ dir_hash_add(
 		}
 	}
 
-	if ((p = malloc(sizeof(*p))) == NULL)
+	/*
+	 * Allocate enough space for the hash entry and the name in a single
+	 * allocation so we can store our own copy of the name for later use.
+	 */
+	p = calloc(1, sizeof(*p) + namelen + 1);
+	if (!p)
 		do_error(_("malloc failed in dir_hash_add (%zu bytes)\n"),
 			sizeof(*p));
 
@@ -220,8 +223,12 @@ dir_hash_add(
 	p->address = addr;
 	p->inum = inum;
 	p->seen = 0;
-	p->name = xname;
 
+	/* Set up the name in the region trailing the hash entry. */
+	memcpy(p->namebuf, name, namelen);
+	p->name.name = p->namebuf;
+	p->name.len = namelen;
+	p->name.type = ftype;
 	return !dup;
 }
 
@@ -287,8 +294,6 @@ dir_hash_done(
 	for (i = 0; i < hashtab->size; i++) {
 		for (p = hashtab->byaddr[i]; p; p = n) {
 			n = p->nextbyaddr;
-			if (hashtab->names_duped)
-				free((void *)p->name.name);
 			free(p);
 		}
 	}
@@ -385,27 +390,6 @@ dir_hash_see_all(
 	return j == stale ? DIR_HASH_CK_OK : DIR_HASH_CK_BADSTALE;
 }
 
-/*
- * Convert name pointers into locally allocated memory.
- * This must only be done after all the entries have been added.
- */
-static void
-dir_hash_dup_names(dir_hash_tab_t *hashtab)
-{
-	unsigned char		*name;
-	dir_hash_ent_t		*p;
-
-	if (hashtab->names_duped)
-		return;
-
-	for (p = hashtab->first; p; p = p->nextbyorder) {
-		name = malloc(p->name.len);
-		memcpy(name, p->name.name, p->name.len);
-		p->name.name = name;
-	}
-	hashtab->names_duped = 1;
-}
-
 /*
  * Given a block number in a fork, return the next valid block number (not a
  * hole).  If this is the last block number then NULLFILEOFF is returned.
@@ -1383,6 +1367,7 @@ dir2_kill_block(
 		res_failed(error);
 	libxfs_trans_ijoin(tp, ip, 0);
 	libxfs_trans_bjoin(tp, bp);
+	libxfs_trans_bhold(tp, bp);
 	memset(&args, 0, sizeof(args));
 	args.dp = ip;
 	args.trans = tp;
@@ -1414,7 +1399,7 @@ longform_dir2_entry_check_data(
 	int			*need_dot,
 	ino_tree_node_t		*current_irec,
 	int			current_ino_offset,
-	struct xfs_buf		**bpp,
+	struct xfs_buf		*bp,
 	dir_hash_tab_t		*hashtab,
 	freetab_t		**freetabp,
 	xfs_dablk_t		da_bno,
@@ -1422,7 +1407,6 @@ longform_dir2_entry_check_data(
 {
 	xfs_dir2_dataptr_t	addr;
 	xfs_dir2_leaf_entry_t	*blp;
-	struct xfs_buf		*bp;
 	xfs_dir2_block_tail_t	*btp;
 	struct xfs_dir2_data_hdr *d;
 	xfs_dir2_db_t		db;
@@ -1453,7 +1437,6 @@ longform_dir2_entry_check_data(
 	};
 
 
-	bp = *bpp;
 	d = bp->b_addr;
 	ptr = (char *)d + mp->m_dir_geo->data_entry_offset;
 	nbad = 0;
@@ -1554,10 +1537,8 @@ longform_dir2_entry_check_data(
 			dir2_kill_block(mp, ip, da_bno, bp);
 		} else {
 			do_warn(_("would junk block\n"));
-			libxfs_buf_relse(bp);
 		}
 		freetab->ents[db].v = NULLDATAOFF;
-		*bpp = NULL;
 		return;
 	}
 
@@ -2215,17 +2196,15 @@ longform_dir2_entry_check(xfs_mount_t	*mp,
 			int		ino_offset,
 			dir_hash_tab_t	*hashtab)
 {
-	struct xfs_buf		**bplist;
+	struct xfs_buf		*bp;
 	xfs_dablk_t		da_bno;
 	freetab_t		*freetab;
-	int			num_bps;
 	int			i;
 	int			isblock;
 	int			isleaf;
 	xfs_fileoff_t		next_da_bno;
 	int			seeval;
 	int			fixit = 0;
-	xfs_dir2_db_t		db;
 	struct xfs_da_args	args;
 
 	*need_dot = 1;
@@ -2242,11 +2221,6 @@ longform_dir2_entry_check(xfs_mount_t	*mp,
 		freetab->ents[i].v = NULLDATAOFF;
 		freetab->ents[i].s = 0;
 	}
-	num_bps = freetab->naents;
-	bplist = calloc(num_bps, sizeof(struct xfs_buf*));
-	if (!bplist)
-		do_error(_("calloc failed in %s (%zu bytes)\n"),
-			__func__, num_bps * sizeof(struct xfs_buf*));
 
 	/* is this a block, leaf, or node directory? */
 	args.dp = ip;
@@ -2275,28 +2249,12 @@ longform_dir2_entry_check(xfs_mount_t	*mp,
 			break;
 		}
 
-		db = xfs_dir2_da_to_db(mp->m_dir_geo, da_bno);
-		if (db >= num_bps) {
-			int last_size = num_bps;
-
-			/* more data blocks than expected */
-			num_bps = db + 1;
-			bplist = realloc(bplist, num_bps * sizeof(struct xfs_buf*));
-			if (!bplist)
-				do_error(_("realloc failed in %s (%zu bytes)\n"),
-					__func__,
-					num_bps * sizeof(struct xfs_buf*));
-			/* Initialize the new elements */
-			for (i = last_size; i < num_bps; i++)
-				bplist[i] = NULL;
-		}
-
 		if (isblock)
 			ops = &xfs_dir3_block_buf_ops;
 		else
 			ops = &xfs_dir3_data_buf_ops;
 
-		error = dir_read_buf(ip, da_bno, &bplist[db], ops, &fixit);
+		error = dir_read_buf(ip, da_bno, &bp, ops, &fixit);
 		if (error) {
 			do_warn(
 	_("can't read data block %u for directory inode %" PRIu64 " error %d\n"),
@@ -2316,21 +2274,25 @@ longform_dir2_entry_check(xfs_mount_t	*mp,
 		}
 
 		/* check v5 metadata */
-		d = bplist[db]->b_addr;
+		d = bp->b_addr;
 		if (be32_to_cpu(d->magic) == XFS_DIR3_BLOCK_MAGIC ||
 		    be32_to_cpu(d->magic) == XFS_DIR3_DATA_MAGIC) {
-			struct xfs_buf		 *bp = bplist[db];
-
 			error = check_dir3_header(mp, bp, ino);
 			if (error) {
 				fixit++;
+				if (isblock)
+					goto out_fix;
 				continue;
 			}
 		}
 
 		longform_dir2_entry_check_data(mp, ip, num_illegal, need_dot,
-				irec, ino_offset, &bplist[db], hashtab,
+				irec, ino_offset, bp, hashtab,
 				&freetab, da_bno, isblock);
+		if (isblock)
+			break;
+
+		libxfs_buf_relse(bp);
 	}
 	fixit |= (*num_illegal != 0) || dir2_is_badino(ino) || *need_dot;
 
@@ -2341,7 +2303,7 @@ longform_dir2_entry_check(xfs_mount_t	*mp,
 			xfs_dir2_block_tail_t	*btp;
 			xfs_dir2_leaf_entry_t	*blp;
 
-			block = bplist[0]->b_addr;
+			block = bp->b_addr;
 			btp = xfs_dir2_block_tail_p(mp->m_dir_geo, block);
 			blp = xfs_dir2_block_leaf_p(btp);
 			seeval = dir_hash_see_all(hashtab, blp,
@@ -2358,11 +2320,10 @@ longform_dir2_entry_check(xfs_mount_t	*mp,
 		}
 	}
 out_fix:
+	if (isblock && bp)
+		libxfs_buf_relse(bp);
+
 	if (!no_modify && (fixit || dotdot_update)) {
-		dir_hash_dup_names(hashtab);
-		for (i = 0; i < num_bps; i++)
-			if (bplist[i])
-				libxfs_buf_relse(bplist[i]);
 		longform_dir2_rebuild(mp, ino, ip, irec, ino_offset, hashtab);
 		*num_illegal = 0;
 		*need_dot = 0;
@@ -2370,12 +2331,8 @@ out_fix:
 		if (fixit || dotdot_update)
 			do_warn(
 	_("would rebuild directory inode %" PRIu64 "\n"), ino);
-		for (i = 0; i < num_bps; i++)
-			if (bplist[i])
-				libxfs_buf_relse(bplist[i]);
 	}
 
-	free(bplist);
 	free(freetab);
 }
 
-- 
2.20.1

[PATCH v3 7/8] repair: convert the dir byaddr hash to a radix tree

[Gao Xiang]

From: Dave Chinner <dchinner@redhat.com>

Phase 6 uses a hash table to track the data segment addresses of the
entries it has seen in a directory. This is indexed by the offset
into the data segment for the dirent, and is used to check if the
entry exists, is a duplicate or has a bad hash value. The lookup
operations involve walking long hash chains on large directories and
they are done for every entry in the directory. This means certain
operations have O(n^2) scalability (or worse!) and hence hurt on
very large directories.

It is also used to determine if the directory has unseen entries,
which involves a full hash traversal that is very expensive on large
directories. Hence the directory checking for unseen ends up being
roughly a O(n^2 + n) algorithm.

Switch the byaddr indexing to a radix tree. While a radix tree will
burn more memory than the linked list, it gives us O(log n) lookup
operations instead of O(n) on large directories, and use for tags
gives us O(1) determination of whether all entries have been seen or
not. This brings the "entry seen" algorithm scalability back to
O(nlog n) and so is a major improvement for processing large
directories.

Given a filesystem with 10M empty files in a single directory, we
see:

5.6.0:

  97.56%  xfs_repair              [.] dir_hash_add.lto_priv.0
   0.38%  xfs_repair              [.] avl_ino_start.lto_priv.0
   0.37%  libc-2.31.so            [.] malloc
   0.34%  xfs_repair              [.] longform_dir2_entry_check_data.lto_priv.0

Phase 6:        10/22 12:07:13  10/22 12:10:51  3 minutes, 38 seconds

Patched:

  97.11%  xfs_repair          [.] dir_hash_add
   0.38%  xfs_repair          [.] longform_dir2_entry_check_data
   0.34%  libc-2.31.so        [.] __libc_calloc
   0.32%  xfs_repair          [.] avl_ino_start

Phase 6:        10/22 12:11:40  10/22 12:14:28  2 minutes, 48 seconds

So there's some improvement, but we are clearly still CPU bound due
to the O(n^2) scalability of the duplicate name checking algorithm.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 libfrog/radix-tree.c |  46 +++++++++
 repair/phase6.c      | 222 ++++++++++++++++++++-----------------------
 2 files changed, 148 insertions(+), 120 deletions(-)

diff --git a/libfrog/radix-tree.c b/libfrog/radix-tree.c
index c1c74876964c..261fc2487de9 100644
--- a/libfrog/radix-tree.c
+++ b/libfrog/radix-tree.c
@@ -312,6 +312,52 @@ void *radix_tree_lookup_first(struct radix_tree_root *root, unsigned long *index
 
 #ifdef RADIX_TREE_TAGS
 
+/**
+ * radix_tree_tag_get - get a tag on a radix tree node
+ * @root:		radix tree root
+ * @index:		index key
+ * @tag:		tag index (< RADIX_TREE_MAX_TAGS)
+ *
+ * Return values:
+ *
+ *  0: tag not present or not set
+ *  1: tag set
+ *
+ * Note that the return value of this function may not be relied on, even if
+ * the RCU lock is held, unless tag modification and node deletion are excluded
+ * from concurrency.
+ */
+int radix_tree_tag_get(struct radix_tree_root *root,
+			unsigned long index, unsigned int tag)
+{
+	unsigned int height, shift;
+	struct radix_tree_node *slot;
+
+	height = root->height;
+	if (index > radix_tree_maxindex(height))
+		return 0;
+
+	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
+	slot = root->rnode;
+
+	while (height > 0) {
+		int offset;
+
+		if (slot == NULL)
+			return 0;
+
+		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
+		if (!tag_get(slot, tag, offset))
+			return 0;
+
+		slot = slot->slots[offset];
+		ASSERT(slot != NULL);
+		shift -= RADIX_TREE_MAP_SHIFT;
+		height--;
+	}
+	return 1;
+}
+
 /**
  *	radix_tree_tag_set - set a tag on a radix tree node
  *	@root:		radix tree root
diff --git a/repair/phase6.c b/repair/phase6.c
index df8db146c187..063329636500 100644
--- a/repair/phase6.c
+++ b/repair/phase6.c
@@ -66,8 +66,7 @@ add_dotdot_update(
  * and whether their leaf entry has been seen. Also used for name
  * duplicate checking and rebuilding step if required.
  */
-typedef struct dir_hash_ent {
-	struct dir_hash_ent	*nextbyaddr;	/* next in addr bucket */
+struct dir_hash_ent {
 	struct dir_hash_ent	*nextbyhash;	/* next in name bucket */
 	struct dir_hash_ent	*nextbyorder;	/* next in order added */
 	xfs_dahash_t		hashval;	/* hash value of name */
@@ -77,18 +76,19 @@ typedef struct dir_hash_ent {
 	short			seen;		/* have seen leaf entry */
 	struct xfs_name		name;
 	unsigned char		namebuf[];
-} dir_hash_ent_t;
+};
 
-typedef struct dir_hash_tab {
+struct dir_hash_tab {
 	int			size;		/* size of hash tables */
-	dir_hash_ent_t		*first;		/* ptr to first added entry */
-	dir_hash_ent_t		*last;		/* ptr to last added entry */
-	dir_hash_ent_t		**byhash;	/* ptr to name hash buckets */
-	dir_hash_ent_t		**byaddr;	/* ptr to addr hash buckets */
-} dir_hash_tab_t;
+	struct dir_hash_ent	*first;		/* ptr to first added entry */
+	struct dir_hash_ent	*last;		/* ptr to last added entry */
+	struct dir_hash_ent	**byhash;	/* ptr to name hash buckets */
+#define HT_UNSEEN		1
+	struct radix_tree_root	byaddr;
+};
 
 #define	DIR_HASH_TAB_SIZE(n)	\
-	(sizeof(dir_hash_tab_t) + (sizeof(dir_hash_ent_t *) * (n) * 2))
+	(sizeof(struct dir_hash_tab) + (sizeof(struct dir_hash_ent *) * (n)))
 #define	DIR_HASH_FUNC(t,a)	((a) % (t)->size)
 
 /*
@@ -155,8 +155,8 @@ dir_read_buf(
  */
 static int
 dir_hash_add(
-	xfs_mount_t		*mp,
-	dir_hash_tab_t		*hashtab,
+	struct xfs_mount	*mp,
+	struct dir_hash_tab	*hashtab,
 	uint32_t		addr,
 	xfs_ino_t		inum,
 	int			namelen,
@@ -164,19 +164,18 @@ dir_hash_add(
 	uint8_t			ftype)
 {
 	xfs_dahash_t		hash = 0;
-	int			byaddr;
 	int			byhash = 0;
-	dir_hash_ent_t		*p;
+	struct dir_hash_ent	*p;
 	int			dup;
 	short			junk;
 	struct xfs_name		xname;
+	int			error;
 
 	xname.name = name;
 	xname.len = namelen;
 	xname.type = ftype;
 
 	junk = name[0] == '/';
-	byaddr = DIR_HASH_FUNC(hashtab, addr);
 	dup = 0;
 
 	if (!junk) {
@@ -206,8 +205,14 @@ dir_hash_add(
 		do_error(_("malloc failed in dir_hash_add (%zu bytes)\n"),
 			sizeof(*p));
 
-	p->nextbyaddr = hashtab->byaddr[byaddr];
-	hashtab->byaddr[byaddr] = p;
+	error = radix_tree_insert(&hashtab->byaddr, addr, p);
+	if (error == EEXIST) {
+		do_warn(_("duplicate addrs %u in directory!\n"), addr);
+		free(p);
+		return 0;
+	}
+	radix_tree_tag_set(&hashtab->byaddr, addr, HT_UNSEEN);
+
 	if (hashtab->last)
 		hashtab->last->nextbyorder = p;
 	else
@@ -232,33 +237,14 @@ dir_hash_add(
 	return !dup;
 }
 
-/*
- * checks to see if any data entries are not in the leaf blocks
- */
-static int
-dir_hash_unseen(
-	dir_hash_tab_t	*hashtab)
-{
-	int		i;
-	dir_hash_ent_t	*p;
-
-	for (i = 0; i < hashtab->size; i++) {
-		for (p = hashtab->byaddr[i]; p; p = p->nextbyaddr) {
-			if (p->seen == 0)
-				return 1;
-		}
-	}
-	return 0;
-}
-
 static int
 dir_hash_check(
-	dir_hash_tab_t	*hashtab,
-	xfs_inode_t	*ip,
-	int		seeval)
+	struct dir_hash_tab	*hashtab,
+	struct xfs_inode	*ip,
+	int			seeval)
 {
-	static char	*seevalstr[DIR_HASH_CK_TOTAL];
-	static int	done;
+	static char		*seevalstr[DIR_HASH_CK_TOTAL];
+	static int		done;
 
 	if (!done) {
 		seevalstr[DIR_HASH_CK_OK] = _("ok");
@@ -270,7 +256,8 @@ dir_hash_check(
 		done = 1;
 	}
 
-	if (seeval == DIR_HASH_CK_OK && dir_hash_unseen(hashtab))
+	if (seeval == DIR_HASH_CK_OK &&
+	    radix_tree_tagged(&hashtab->byaddr, HT_UNSEEN))
 		seeval = DIR_HASH_CK_NOLEAF;
 	if (seeval == DIR_HASH_CK_OK)
 		return 0;
@@ -285,27 +272,28 @@ dir_hash_check(
 
 static void
 dir_hash_done(
-	dir_hash_tab_t	*hashtab)
+	struct dir_hash_tab	*hashtab)
 {
-	int		i;
-	dir_hash_ent_t	*n;
-	dir_hash_ent_t	*p;
+	int			i;
+	struct dir_hash_ent	*n;
+	struct dir_hash_ent	*p;
 
 	for (i = 0; i < hashtab->size; i++) {
-		for (p = hashtab->byaddr[i]; p; p = n) {
-			n = p->nextbyaddr;
+		for (p = hashtab->byhash[i]; p; p = n) {
+			n = p->nextbyhash;
+			radix_tree_delete(&hashtab->byaddr, p->address);
 			free(p);
 		}
 	}
 	free(hashtab);
 }
 
-static dir_hash_tab_t *
+static struct dir_hash_tab *
 dir_hash_init(
-	xfs_fsize_t	size)
+	xfs_fsize_t		size)
 {
-	dir_hash_tab_t	*hashtab;
-	int		hsize;
+	struct dir_hash_tab	*hashtab;
+	int			hsize;
 
 	hsize = size / (16 * 4);
 	if (hsize > 65536)
@@ -315,51 +303,43 @@ dir_hash_init(
 	if ((hashtab = calloc(DIR_HASH_TAB_SIZE(hsize), 1)) == NULL)
 		do_error(_("calloc failed in dir_hash_init\n"));
 	hashtab->size = hsize;
-	hashtab->byhash = (dir_hash_ent_t**)((char *)hashtab +
-		sizeof(dir_hash_tab_t));
-	hashtab->byaddr = (dir_hash_ent_t**)((char *)hashtab +
-		sizeof(dir_hash_tab_t) + sizeof(dir_hash_ent_t*) * hsize);
+	hashtab->byhash = (struct dir_hash_ent **)((char *)hashtab +
+		sizeof(struct dir_hash_tab));
+	INIT_RADIX_TREE(&hashtab->byaddr, 0);
 	return hashtab;
 }
 
 static int
 dir_hash_see(
-	dir_hash_tab_t		*hashtab,
+	struct dir_hash_tab	*hashtab,
 	xfs_dahash_t		hash,
 	xfs_dir2_dataptr_t	addr)
 {
-	int			i;
-	dir_hash_ent_t		*p;
+	struct dir_hash_ent	*p;
 
-	i = DIR_HASH_FUNC(hashtab, addr);
-	for (p = hashtab->byaddr[i]; p; p = p->nextbyaddr) {
-		if (p->address != addr)
-			continue;
-		if (p->seen)
-			return DIR_HASH_CK_DUPLEAF;
-		if (p->junkit == 0 && p->hashval != hash)
-			return DIR_HASH_CK_BADHASH;
-		p->seen = 1;
-		return DIR_HASH_CK_OK;
-	}
-	return DIR_HASH_CK_NODATA;
+	p = radix_tree_lookup(&hashtab->byaddr, addr);
+	if (!p)
+		return DIR_HASH_CK_NODATA;
+	if (!radix_tree_tag_get(&hashtab->byaddr, addr, HT_UNSEEN))
+		return DIR_HASH_CK_DUPLEAF;
+	if (p->junkit == 0 && p->hashval != hash)
+		return DIR_HASH_CK_BADHASH;
+	radix_tree_tag_clear(&hashtab->byaddr, addr, HT_UNSEEN);
+	return DIR_HASH_CK_OK;
 }
 
 static void
 dir_hash_update_ftype(
-	dir_hash_tab_t		*hashtab,
+	struct dir_hash_tab	*hashtab,
 	xfs_dir2_dataptr_t	addr,
 	uint8_t			ftype)
 {
-	int			i;
-	dir_hash_ent_t		*p;
+	struct dir_hash_ent	*p;
 
-	i = DIR_HASH_FUNC(hashtab, addr);
-	for (p = hashtab->byaddr[i]; p; p = p->nextbyaddr) {
-		if (p->address != addr)
-			continue;
-		p->name.type = ftype;
-	}
+	p = radix_tree_lookup(&hashtab->byaddr, addr);
+	if (!p)
+		return;
+	p->name.type = ftype;
 }
 
 /*
@@ -368,7 +348,7 @@ dir_hash_update_ftype(
  */
 static int
 dir_hash_see_all(
-	dir_hash_tab_t		*hashtab,
+	struct dir_hash_tab	*hashtab,
 	xfs_dir2_leaf_entry_t	*ents,
 	int			count,
 	int			stale)
@@ -1222,19 +1202,19 @@ dir_binval(
 
 static void
 longform_dir2_rebuild(
-	xfs_mount_t		*mp,
+	struct xfs_mount	*mp,
 	xfs_ino_t		ino,
-	xfs_inode_t		*ip,
-	ino_tree_node_t		*irec,
+	struct xfs_inode	*ip,
+	struct ino_tree_node	*irec,
 	int			ino_offset,
-	dir_hash_tab_t		*hashtab)
+	struct dir_hash_tab	*hashtab)
 {
 	int			error;
 	int			nres;
-	xfs_trans_t		*tp;
+	struct xfs_trans	*tp;
 	xfs_fileoff_t		lastblock;
-	xfs_inode_t		pip;
-	dir_hash_ent_t		*p;
+	struct xfs_inode	pip;
+	struct dir_hash_ent	*p;
 	int			done = 0;
 
 	/*
@@ -1393,14 +1373,14 @@ _("directory shrink failed (%d)\n"), error);
  */
 static void
 longform_dir2_entry_check_data(
-	xfs_mount_t		*mp,
-	xfs_inode_t		*ip,
+	struct xfs_mount	*mp,
+	struct xfs_inode	*ip,
 	int			*num_illegal,
 	int			*need_dot,
-	ino_tree_node_t		*current_irec,
+	struct ino_tree_node	*current_irec,
 	int			current_ino_offset,
 	struct xfs_buf		*bp,
-	dir_hash_tab_t		*hashtab,
+	struct dir_hash_tab	*hashtab,
 	freetab_t		**freetabp,
 	xfs_dablk_t		da_bno,
 	int			isblock)
@@ -1927,10 +1907,10 @@ check_dir3_header(
  */
 static int
 longform_dir2_check_leaf(
-	xfs_mount_t		*mp,
-	xfs_inode_t		*ip,
-	dir_hash_tab_t		*hashtab,
-	freetab_t		*freetab)
+	struct xfs_mount	*mp,
+	struct xfs_inode	*ip,
+	struct dir_hash_tab	*hashtab,
+	struct freetab		*freetab)
 {
 	int			badtail;
 	__be16			*bestsp;
@@ -2012,10 +1992,10 @@ longform_dir2_check_leaf(
  */
 static int
 longform_dir2_check_node(
-	xfs_mount_t		*mp,
-	xfs_inode_t		*ip,
-	dir_hash_tab_t		*hashtab,
-	freetab_t		*freetab)
+	struct xfs_mount	*mp,
+	struct xfs_inode	*ip,
+	struct dir_hash_tab	*hashtab,
+	struct freetab		*freetab)
 {
 	struct xfs_buf		*bp;
 	xfs_dablk_t		da_bno;
@@ -2187,14 +2167,15 @@ longform_dir2_check_node(
  * (ie. get libxfs to do all the grunt work)
  */
 static void
-longform_dir2_entry_check(xfs_mount_t	*mp,
-			xfs_ino_t	ino,
-			xfs_inode_t	*ip,
-			int		*num_illegal,
-			int		*need_dot,
-			ino_tree_node_t	*irec,
-			int		ino_offset,
-			dir_hash_tab_t	*hashtab)
+longform_dir2_entry_check(
+	struct xfs_mount	*mp,
+	xfs_ino_t		ino,
+	struct xfs_inode	*ip,
+	int			*num_illegal,
+	int			*need_dot,
+	struct ino_tree_node	*irec,
+	int			ino_offset,
+	struct dir_hash_tab	*hashtab)
 {
 	struct xfs_buf		*bp;
 	xfs_dablk_t		da_bno;
@@ -2397,13 +2378,14 @@ shortform_dir2_junk(
 }
 
 static void
-shortform_dir2_entry_check(xfs_mount_t	*mp,
-			xfs_ino_t	ino,
-			xfs_inode_t	*ip,
-			int		*ino_dirty,
-			ino_tree_node_t	*current_irec,
-			int		current_ino_offset,
-			dir_hash_tab_t	*hashtab)
+shortform_dir2_entry_check(
+	struct xfs_mount	*mp,
+	xfs_ino_t		ino,
+	struct xfs_inode	*ip,
+	int			*ino_dirty,
+	struct ino_tree_node	*current_irec,
+	int			current_ino_offset,
+	struct dir_hash_tab	*hashtab)
 {
 	xfs_ino_t		lino;
 	xfs_ino_t		parent;
@@ -2745,15 +2727,15 @@ _("entry \"%s\" (ino %" PRIu64 ") in dir %" PRIu64 " is a duplicate name"),
  */
 static void
 process_dir_inode(
-	xfs_mount_t 		*mp,
+	struct xfs_mount	*mp,
 	xfs_agnumber_t		agno,
-	ino_tree_node_t		*irec,
+	struct ino_tree_node	*irec,
 	int			ino_offset)
 {
 	xfs_ino_t		ino;
-	xfs_inode_t		*ip;
-	xfs_trans_t		*tp;
-	dir_hash_tab_t		*hashtab;
+	struct xfs_inode	*ip;
+	struct xfs_trans	*tp;
+	struct dir_hash_tab	*hashtab;
 	int			need_dot;
 	int			dirty, num_illegal, error, nres;
 
-- 
2.20.1

[PATCH v3 8/8] repair: scale duplicate name checking in phase 6.

[Gao Xiang]

From: Dave Chinner <dchinner@redhat.com>

phase 6 on large directories is cpu bound on duplicate name checking
due to the algorithm having effectively O(n^2) scalability. Hence
when the duplicate name hash table  size is far smaller than the
number of directory entries, we end up with long hash chains that
are searched linearly on every new entry that is found in the
directory to do duplicate detection.

The in-memory hash table size is limited to 64k entries. Hence when
we have millions of entries in a directory, duplicate entry lookups
on the hash table have substantial overhead. Scale this table out to
larger sizes so that we keep the chain lengths short and hence the
O(n^2) scalability impact is limited because N is always small.

For a 10M entry directory consuming 400MB of directory data, the
hash table now sizes at 6.4 million entries instead of ~64k - it is
~100x larger. While the hash table now consumes ~50MB of RAM, the
xfs_repair footprint barely changes as it's using already consuming
~9GB of RAM at this point in time. IOWs, the incremental memory
usage change is noise, but the directory checking time:

Unpatched:

  97.11%  xfs_repair          [.] dir_hash_add
   0.38%  xfs_repair          [.] longform_dir2_entry_check_data
   0.34%  libc-2.31.so        [.] __libc_calloc
   0.32%  xfs_repair          [.] avl_ino_start

Phase 6:        10/22 12:11:40  10/22 12:14:28  2 minutes, 48 seconds

Patched:

  46.74%  xfs_repair          [.] radix_tree_lookup
  32.13%  xfs_repair          [.] dir_hash_see_all
   7.70%  xfs_repair          [.] radix_tree_tag_get
   3.92%  xfs_repair          [.] dir_hash_add
   3.52%  xfs_repair          [.] radix_tree_tag_clear
   2.43%  xfs_repair          [.] crc32c_le

Phase 6:        10/22 13:11:01  10/22 13:11:18  17 seconds

has been reduced by an order of magnitude.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 repair/phase6.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/repair/phase6.c b/repair/phase6.c
index 063329636500..aa991bf76da6 100644
--- a/repair/phase6.c
+++ b/repair/phase6.c
@@ -288,19 +288,37 @@ dir_hash_done(
 	free(hashtab);
 }
 
+/*
+ * Create a directory hash index structure based on the size of the directory we
+ * are about to try to repair. The size passed in is the size of the data
+ * segment of the directory in bytes, so we don't really know exactly how many
+ * entries are in it. Hence assume an entry size of around 64 bytes - that's a
+ * name length of 40+ bytes so should cover a most situations with large
+ * really directories.
+ */
 static struct dir_hash_tab *
 dir_hash_init(
 	xfs_fsize_t		size)
 {
-	struct dir_hash_tab	*hashtab;
+	struct dir_hash_tab	*hashtab = NULL;
 	int			hsize;
 
-	hsize = size / (16 * 4);
-	if (hsize > 65536)
-		hsize = 63336;
-	else if (hsize < 16)
+	hsize = size / 64;
+	if (hsize < 16)
 		hsize = 16;
-	if ((hashtab = calloc(DIR_HASH_TAB_SIZE(hsize), 1)) == NULL)
+
+	/*
+	 * Try to allocate as large a hash table as possible. Failure to
+	 * allocate isn't fatal, it will just result in slower performance as we
+	 * reduce the size of the table.
+	 */
+	while (hsize >= 16) {
+		hashtab = calloc(DIR_HASH_TAB_SIZE(hsize), 1);
+		if (hashtab)
+			break;
+		hsize /= 2;
+	}
+	if (!hashtab)
 		do_error(_("calloc failed in dir_hash_init\n"));
 	hashtab->size = hsize;
 	hashtab->byhash = (struct dir_hash_ent **)((char *)hashtab +
-- 
2.20.1

Re: [PATCH v3 8/8] repair: scale duplicate name checking in phase 6.

[Darrick J. Wong]

On Tue, Mar 30, 2021 at 10:25:31PM +0800, Gao Xiang wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> phase 6 on large directories is cpu bound on duplicate name checking
> due to the algorithm having effectively O(n^2) scalability. Hence
> when the duplicate name hash table  size is far smaller than the
> number of directory entries, we end up with long hash chains that
> are searched linearly on every new entry that is found in the
> directory to do duplicate detection.
> 
> The in-memory hash table size is limited to 64k entries. Hence when
> we have millions of entries in a directory, duplicate entry lookups
> on the hash table have substantial overhead. Scale this table out to
> larger sizes so that we keep the chain lengths short and hence the
> O(n^2) scalability impact is limited because N is always small.
> 
> For a 10M entry directory consuming 400MB of directory data, the
> hash table now sizes at 6.4 million entries instead of ~64k - it is
> ~100x larger. While the hash table now consumes ~50MB of RAM, the
> xfs_repair footprint barely changes as it's using already consuming
> ~9GB of RAM at this point in time. IOWs, the incremental memory
> usage change is noise, but the directory checking time:
> 
> Unpatched:
> 
>   97.11%  xfs_repair          [.] dir_hash_add
>    0.38%  xfs_repair          [.] longform_dir2_entry_check_data
>    0.34%  libc-2.31.so        [.] __libc_calloc
>    0.32%  xfs_repair          [.] avl_ino_start
> 
> Phase 6:        10/22 12:11:40  10/22 12:14:28  2 minutes, 48 seconds
> 
> Patched:
> 
>   46.74%  xfs_repair          [.] radix_tree_lookup
>   32.13%  xfs_repair          [.] dir_hash_see_all
>    7.70%  xfs_repair          [.] radix_tree_tag_get
>    3.92%  xfs_repair          [.] dir_hash_add
>    3.52%  xfs_repair          [.] radix_tree_tag_clear
>    2.43%  xfs_repair          [.] crc32c_le
> 
> Phase 6:        10/22 13:11:01  10/22 13:11:18  17 seconds
> 
> has been reduced by an order of magnitude.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> ---
>  repair/phase6.c | 30 ++++++++++++++++++++++++------
>  1 file changed, 24 insertions(+), 6 deletions(-)
> 
> diff --git a/repair/phase6.c b/repair/phase6.c
> index 063329636500..aa991bf76da6 100644
> --- a/repair/phase6.c
> +++ b/repair/phase6.c
> @@ -288,19 +288,37 @@ dir_hash_done(
>  	free(hashtab);
>  }
>  
> +/*
> + * Create a directory hash index structure based on the size of the directory we
> + * are about to try to repair. The size passed in is the size of the data
> + * segment of the directory in bytes, so we don't really know exactly how many
> + * entries are in it. Hence assume an entry size of around 64 bytes - that's a
> + * name length of 40+ bytes so should cover a most situations with large
> + * really directories.

"...with really large directories."

> + */
>  static struct dir_hash_tab *
>  dir_hash_init(
>  	xfs_fsize_t		size)
>  {
> -	struct dir_hash_tab	*hashtab;
> +	struct dir_hash_tab	*hashtab = NULL;
>  	int			hsize;
>  
> -	hsize = size / (16 * 4);
> -	if (hsize > 65536)
> -		hsize = 63336;
> -	else if (hsize < 16)
> +	hsize = size / 64;
> +	if (hsize < 16)
>  		hsize = 16;
> -	if ((hashtab = calloc(DIR_HASH_TAB_SIZE(hsize), 1)) == NULL)
> +
> +	/*
> +	 * Try to allocate as large a hash table as possible. Failure to
> +	 * allocate isn't fatal, it will just result in slower performance as we
> +	 * reduce the size of the table.
> +	 */
> +	while (hsize >= 16) {
> +		hashtab = calloc(DIR_HASH_TAB_SIZE(hsize), 1);
> +		if (hashtab)
> +			break;
> +		hsize /= 2;
> +	}

I still kinda wonder if the hash size ought to be some prime number,
though I suppose /finding/ a prime number isn't necessarily easy.

Hm, let's assume you had the maximal 32GB directory.

size = 34359738368
hsize = size/64 = 536870912
DIR_HASH_TAB_SIZE(hsize) =
	(sizeof(dir_hash_tab_t) + (sizeof(dir_hash_ent_t *) * (hsize) * 2))

== 40 + (8 * 536870912 * 2) == 8589934632

That's ... kind of big?  I guess the saving grace is that we halve hsize
if calloc fails and the address space isn't populated with memory pages
until we actually use them.  It might turn out that users want a lower
cap than 8GB per 32GB directory, but I suppose we won't find /that/ out
until we try...

With the comment fixed,

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> +	if (!hashtab)
>  		do_error(_("calloc failed in dir_hash_init\n"));
>  	hashtab->size = hsize;
>  	hashtab->byhash = (struct dir_hash_ent **)((char *)hashtab +
> -- 
> 2.20.1
>