[PATCH 0/4] improved busy extent handling V5

[PATCH 0/4] improved busy extent handling V5

[Christoph Hellwig]

This series optimizes how XFS deals with busy extents.  It starts to
track them exactly, and allows reuses where possible (metadata to metadata)
or else tries to avoid busy extents during allocations.  This means
we don't have a single log force due to busy extents during either
xfstests, compilebench or postmark on my testsystem, which can easily
be tracked using the new tracepoints added in the last patch.

Changes from V4:
 - fix xfs_alloc_busy_trim tracing
Changes from V3:
 - address review comments from Alex in patch 2
 - add a new patch to reduce pagb_lock roundtrips
Changes from V2:
 - remove the bmapi userdata tracking now that is unused
 - restructure the busy extent reuse code to make it more suitable
   for the discard support
 - reshuffle the patch boundaries

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[PATCH 1/4] xfs: optimize AGFL refills

[Christoph Hellwig]

[-- Attachment #1: xfs-optimize-freelist-refills --]
[-- Type: text/plain, Size: 3699 bytes --]

While we need to make sure we do not reuse busy extents, there is no need
to force out busy extents when moving them between the AGFL and the
freespace btree as we still take care of that when doing the real allocation.

To avoid the log force when just moving extents from the different free
space tracking structures, move the busy search out of
xfs_alloc_get_freelist into the callers that need it, and move the busy
list insert from xfs_free_ag_extent which is used both by AGFL refills
and real allocation to xfs_free_extent, which is only used by the latter.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>

Index: xfs/fs/xfs/xfs_alloc.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.c	2011-04-09 23:30:52.778449337 +0200
+++ xfs/fs/xfs/xfs_alloc.c	2011-04-15 08:33:19.762528005 +0200
@@ -1326,6 +1326,8 @@ xfs_alloc_ag_vextent_small(
 		if (error)
 			goto error0;
 		if (fbno != NULLAGBLOCK) {
+			if (xfs_alloc_busy_search(args->mp, args->agno, fbno, 1))
+				xfs_trans_set_sync(args->tp);
 			if (args->userdata) {
 				xfs_buf_t	*bp;
 
@@ -1617,18 +1619,6 @@ xfs_free_ag_extent(
 
 	trace_xfs_free_extent(mp, agno, bno, len, isfl, haveleft, haveright);
 
-	/*
-	 * Since blocks move to the free list without the coordination
-	 * used in xfs_bmap_finish, we can't allow block to be available
-	 * for reallocation and non-transaction writing (user data)
-	 * until we know that the transaction that moved it to the free
-	 * list is permanently on disk.  We track the blocks by declaring
-	 * these blocks as "busy"; the busy list is maintained on a per-ag
-	 * basis and each transaction records which entries should be removed
-	 * when the iclog commits to disk.  If a busy block is allocated,
-	 * the iclog is pushed up to the LSN that freed the block.
-	 */
-	xfs_alloc_busy_insert(tp, agno, bno, len);
 	return 0;
 
  error0:
@@ -1923,21 +1913,6 @@ xfs_alloc_get_freelist(
 	xfs_alloc_log_agf(tp, agbp, logflags);
 	*bnop = bno;
 
-	/*
-	 * As blocks are freed, they are added to the per-ag busy list and
-	 * remain there until the freeing transaction is committed to disk.
-	 * Now that we have allocated blocks, this list must be searched to see
-	 * if a block is being reused.  If one is, then the freeing transaction
-	 * must be pushed to disk before this transaction.
-	 *
-	 * We do this by setting the current transaction to a sync transaction
-	 * which guarantees that the freeing transaction is on disk before this
-	 * transaction. This is done instead of a synchronous log force here so
-	 * that we don't sit and wait with the AGF locked in the transaction
-	 * during the log force.
-	 */
-	if (xfs_alloc_busy_search(mp, be32_to_cpu(agf->agf_seqno), bno, 1))
-		xfs_trans_set_sync(tp);
 	return 0;
 }
 
@@ -2423,6 +2398,8 @@ xfs_free_extent(
 	}
 
 	error = xfs_free_ag_extent(tp, args.agbp, args.agno, args.agbno, len, 0);
+	if (!error)
+		xfs_alloc_busy_insert(tp, args.agno, args.agbno, len);
 error0:
 	xfs_perag_put(args.pag);
 	return error;
Index: xfs/fs/xfs/xfs_alloc_btree.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc_btree.c	2011-04-06 16:04:49.962413009 +0200
+++ xfs/fs/xfs/xfs_alloc_btree.c	2011-04-15 08:33:19.762528005 +0200
@@ -94,6 +94,8 @@ xfs_allocbt_alloc_block(
 		*stat = 0;
 		return 0;
 	}
+	if (xfs_alloc_busy_search(cur->bc_mp, cur->bc_private.a.agno, bno, 1))
+		xfs_trans_set_sync(cur->bc_tp);
 
 	xfs_trans_agbtree_delta(cur->bc_tp, 1);
 	new->s = cpu_to_be32(bno);

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Re: [PATCH 1/4] xfs: optimize AGFL refills

[Dave Chinner]

On Sun, Apr 24, 2011 at 03:06:14PM -0400, Christoph Hellwig wrote:
> While we need to make sure we do not reuse busy extents, there is no need
> to force out busy extents when moving them between the AGFL and the
> freespace btree as we still take care of that when doing the real allocation.
> 
> To avoid the log force when just moving extents from the different free
> space tracking structures, move the busy search out of
> xfs_alloc_get_freelist into the callers that need it, and move the busy
> list insert from xfs_free_ag_extent which is used both by AGFL refills
> and real allocation to xfs_free_extent, which is only used by the latter.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Alex Elder <aelder@sgi.com>

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com

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[PATCH 2/4] xfs: do not immediately reuse busy extent ranges

[Christoph Hellwig]

[-- Attachment #1: xfs-skip-busy-extents --]
[-- Type: text/plain, Size: 22492 bytes --]

Every time we reallocate a busy extent, we cause a synchronous log force
to occur to ensure the freeing transaction is on disk before we continue
and use the newly allocated extent.  This is extremely sub-optimal as we
have to mark every transaction with blocks that get reused as synchronous.

Instead of searching the busy extent list after deciding on the extent to
allocate, check each candidate extent during the allocation decisions as
to whether they are in the busy list.  If they are in the busy list, we
trim the busy range out of the extent we have found and determine if that
trimmed range is still OK for allocation. In many cases, this check can
be incorporated into the allocation extent alignment code which already
does trimming of the found extent before determining if it is a valid
candidate for allocation.

Based on earlier patches from Dave Chinner.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>

Index: xfs/fs/xfs/xfs_alloc.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.c	2011-04-22 06:23:52.495828397 +0200
+++ xfs/fs/xfs/xfs_alloc.c	2011-04-22 06:24:39.602239867 +0200
@@ -41,19 +41,13 @@
 #define	XFSA_FIXUP_BNO_OK	1
 #define	XFSA_FIXUP_CNT_OK	2
 
-/*
- * Prototypes for per-ag allocation routines
- */
-
 STATIC int xfs_alloc_ag_vextent_exact(xfs_alloc_arg_t *);
 STATIC int xfs_alloc_ag_vextent_near(xfs_alloc_arg_t *);
 STATIC int xfs_alloc_ag_vextent_size(xfs_alloc_arg_t *);
 STATIC int xfs_alloc_ag_vextent_small(xfs_alloc_arg_t *,
-	xfs_btree_cur_t *, xfs_agblock_t *, xfs_extlen_t *, int *);
-
-/*
- * Internal functions.
- */
+		xfs_btree_cur_t *, xfs_agblock_t *, xfs_extlen_t *, int *);
+STATIC void xfs_alloc_busy_trim(struct xfs_alloc_arg *,
+		xfs_agblock_t, xfs_extlen_t, xfs_agblock_t *, xfs_extlen_t *);
 
 /*
  * Lookup the record equal to [bno, len] in the btree given by cur.
@@ -154,19 +148,21 @@ xfs_alloc_compute_aligned(
 	xfs_extlen_t	*reslen)	/* result length */
 {
 	xfs_agblock_t	bno;
-	xfs_extlen_t	diff;
 	xfs_extlen_t	len;
 
-	if (args->alignment > 1 && foundlen >= args->minlen) {
-		bno = roundup(foundbno, args->alignment);
-		diff = bno - foundbno;
-		len = diff >= foundlen ? 0 : foundlen - diff;
+	/* Trim busy sections out of found extent */
+	xfs_alloc_busy_trim(args, foundbno, foundlen, &bno, &len);
+
+	if (args->alignment > 1 && len >= args->minlen) {
+		xfs_agblock_t	aligned_bno = roundup(bno, args->alignment);
+		xfs_extlen_t	diff = aligned_bno - bno;
+
+		*resbno = aligned_bno;
+		*reslen = diff >= len ? 0 : len - diff;
 	} else {
-		bno = foundbno;
-		len = foundlen;
+		*resbno = bno;
+		*reslen = len;
 	}
-	*resbno = bno;
-	*reslen = len;
 }
 
 /*
@@ -541,16 +537,8 @@ xfs_alloc_ag_vextent(
 		if (error)
 			return error;
 
-		/*
-		 * Search the busylist for these blocks and mark the
-		 * transaction as synchronous if blocks are found. This
-		 * avoids the need to block due to a synchronous log
-		 * force to ensure correct ordering as the synchronous
-		 * transaction will guarantee that for us.
-		 */
-		if (xfs_alloc_busy_search(args->mp, args->agno,
-					args->agbno, args->len))
-			xfs_trans_set_sync(args->tp);
+		ASSERT(!xfs_alloc_busy_search(args->mp, args->agno,
+					      args->agbno, args->len));
 	}
 
 	if (!args->isfl) {
@@ -577,14 +565,14 @@ xfs_alloc_ag_vextent_exact(
 {
 	xfs_btree_cur_t	*bno_cur;/* by block-number btree cursor */
 	xfs_btree_cur_t	*cnt_cur;/* by count btree cursor */
-	xfs_agblock_t	end;	/* end of allocated extent */
 	int		error;
 	xfs_agblock_t	fbno;	/* start block of found extent */
-	xfs_agblock_t	fend;	/* end block of found extent */
 	xfs_extlen_t	flen;	/* length of found extent */
+	xfs_agblock_t	tbno;	/* start block of trimmed extent */
+	xfs_extlen_t	tlen;	/* length of trimmed extent */
+	xfs_agblock_t	tend;	/* end block of trimmed extent */
+	xfs_agblock_t	end;	/* end of allocated extent */
 	int		i;	/* success/failure of operation */
-	xfs_agblock_t	maxend;	/* end of maximal extent */
-	xfs_agblock_t	minend;	/* end of minimal extent */
 	xfs_extlen_t	rlen;	/* length of returned extent */
 
 	ASSERT(args->alignment == 1);
@@ -614,14 +602,22 @@ xfs_alloc_ag_vextent_exact(
 		goto error0;
 	XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
 	ASSERT(fbno <= args->agbno);
-	minend = args->agbno + args->minlen;
-	maxend = args->agbno + args->maxlen;
-	fend = fbno + flen;
 
 	/*
-	 * Give up if the freespace isn't long enough for the minimum request.
+	 * Check for overlapping busy extents.
+	 */
+	xfs_alloc_busy_trim(args, fbno, flen, &tbno, &tlen);
+
+	/*
+	 * Give up if the start of the extent is busy, or the freespace isn't
+	 * long enough for the minimum request.
 	 */
-	if (fend < minend)
+	if (tbno > args->agbno)
+		goto not_found;
+	if (tlen < args->minlen)
+		goto not_found;
+	tend = tbno + tlen;
+	if (tend < args->agbno + args->minlen)
 		goto not_found;
 
 	/*
@@ -630,14 +626,14 @@ xfs_alloc_ag_vextent_exact(
 	 *
 	 * Fix the length according to mod and prod if given.
 	 */
-	end = XFS_AGBLOCK_MIN(fend, maxend);
+	end = XFS_AGBLOCK_MIN(tend, args->agbno + args->maxlen);
 	args->len = end - args->agbno;
 	xfs_alloc_fix_len(args);
 	if (!xfs_alloc_fix_minleft(args))
 		goto not_found;
 
 	rlen = args->len;
-	ASSERT(args->agbno + rlen <= fend);
+	ASSERT(args->agbno + rlen <= tend);
 	end = args->agbno + rlen;
 
 	/*
@@ -686,11 +682,11 @@ xfs_alloc_find_best_extent(
 	struct xfs_btree_cur	**scur,	/* searching cursor */
 	xfs_agblock_t		gdiff,	/* difference for search comparison */
 	xfs_agblock_t		*sbno,	/* extent found by search */
-	xfs_extlen_t		*slen,
-	xfs_extlen_t		*slena,	/* aligned length */
+	xfs_extlen_t		*slen,	/* extent length */
+	xfs_agblock_t		*sbnoa,	/* aligned extent found by search */
+	xfs_extlen_t		*slena,	/* aligned extent length */
 	int			dir)	/* 0 = search right, 1 = search left */
 {
-	xfs_agblock_t		bno;
 	xfs_agblock_t		new;
 	xfs_agblock_t		sdiff;
 	int			error;
@@ -708,16 +704,16 @@ xfs_alloc_find_best_extent(
 		if (error)
 			goto error0;
 		XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
-		xfs_alloc_compute_aligned(args, *sbno, *slen, &bno, slena);
+		xfs_alloc_compute_aligned(args, *sbno, *slen, sbnoa, slena);
 
 		/*
 		 * The good extent is closer than this one.
 		 */
 		if (!dir) {
-			if (bno >= args->agbno + gdiff)
+			if (*sbnoa >= args->agbno + gdiff)
 				goto out_use_good;
 		} else {
-			if (bno <= args->agbno - gdiff)
+			if (*sbnoa <= args->agbno - gdiff)
 				goto out_use_good;
 		}
 
@@ -729,8 +725,8 @@ xfs_alloc_find_best_extent(
 			xfs_alloc_fix_len(args);
 
 			sdiff = xfs_alloc_compute_diff(args->agbno, args->len,
-						       args->alignment, *sbno,
-						       *slen, &new);
+						       args->alignment, *sbnoa,
+						       *slena, &new);
 
 			/*
 			 * Choose closer size and invalidate other cursor.
@@ -780,7 +776,7 @@ xfs_alloc_ag_vextent_near(
 	xfs_agblock_t	gtbnoa;		/* aligned ... */
 	xfs_extlen_t	gtdiff;		/* difference to right side entry */
 	xfs_extlen_t	gtlen;		/* length of right side entry */
-	xfs_extlen_t	gtlena = 0;	/* aligned ... */
+	xfs_extlen_t	gtlena;		/* aligned ... */
 	xfs_agblock_t	gtnew;		/* useful start bno of right side */
 	int		error;		/* error code */
 	int		i;		/* result code, temporary */
@@ -789,9 +785,10 @@ xfs_alloc_ag_vextent_near(
 	xfs_agblock_t	ltbnoa;		/* aligned ... */
 	xfs_extlen_t	ltdiff;		/* difference to left side entry */
 	xfs_extlen_t	ltlen;		/* length of left side entry */
-	xfs_extlen_t	ltlena = 0;	/* aligned ... */
+	xfs_extlen_t	ltlena;		/* aligned ... */
 	xfs_agblock_t	ltnew;		/* useful start bno of left side */
 	xfs_extlen_t	rlen;		/* length of returned extent */
+	int		forced = 0;
 #if defined(DEBUG) && defined(__KERNEL__)
 	/*
 	 * Randomly don't execute the first algorithm.
@@ -800,13 +797,20 @@ xfs_alloc_ag_vextent_near(
 
 	dofirst = random32() & 1;
 #endif
+
+restart:
+	bno_cur_lt = NULL;
+	bno_cur_gt = NULL;
+	ltlen = 0;
+	gtlena = 0;
+	ltlena = 0;
+
 	/*
 	 * Get a cursor for the by-size btree.
 	 */
 	cnt_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
 		args->agno, XFS_BTNUM_CNT);
-	ltlen = 0;
-	bno_cur_lt = bno_cur_gt = NULL;
+
 	/*
 	 * See if there are any free extents as big as maxlen.
 	 */
@@ -822,11 +826,13 @@ xfs_alloc_ag_vextent_near(
 			goto error0;
 		if (i == 0 || ltlen == 0) {
 			xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
+			trace_xfs_alloc_near_noentry(args);
 			return 0;
 		}
 		ASSERT(i == 1);
 	}
 	args->wasfromfl = 0;
+
 	/*
 	 * First algorithm.
 	 * If the requested extent is large wrt the freespaces available
@@ -890,7 +896,7 @@ xfs_alloc_ag_vextent_near(
 			if (args->len < blen)
 				continue;
 			ltdiff = xfs_alloc_compute_diff(args->agbno, args->len,
-				args->alignment, ltbno, ltlen, &ltnew);
+				args->alignment, ltbnoa, ltlena, &ltnew);
 			if (ltnew != NULLAGBLOCK &&
 			    (args->len > blen || ltdiff < bdiff)) {
 				bdiff = ltdiff;
@@ -1042,11 +1048,12 @@ xfs_alloc_ag_vextent_near(
 			args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
 			xfs_alloc_fix_len(args);
 			ltdiff = xfs_alloc_compute_diff(args->agbno, args->len,
-				args->alignment, ltbno, ltlen, &ltnew);
+				args->alignment, ltbnoa, ltlena, &ltnew);
 
 			error = xfs_alloc_find_best_extent(args,
 						&bno_cur_lt, &bno_cur_gt,
-						ltdiff, &gtbno, &gtlen, &gtlena,
+						ltdiff, &gtbno, &gtlen,
+						&gtbnoa, &gtlena,
 						0 /* search right */);
 		} else {
 			ASSERT(gtlena >= args->minlen);
@@ -1057,11 +1064,12 @@ xfs_alloc_ag_vextent_near(
 			args->len = XFS_EXTLEN_MIN(gtlena, args->maxlen);
 			xfs_alloc_fix_len(args);
 			gtdiff = xfs_alloc_compute_diff(args->agbno, args->len,
-				args->alignment, gtbno, gtlen, &gtnew);
+				args->alignment, gtbnoa, gtlena, &gtnew);
 
 			error = xfs_alloc_find_best_extent(args,
 						&bno_cur_gt, &bno_cur_lt,
-						gtdiff, &ltbno, &ltlen, &ltlena,
+						gtdiff, &ltbno, &ltlen,
+						&ltbnoa, &ltlena,
 						1 /* search left */);
 		}
 
@@ -1073,6 +1081,12 @@ xfs_alloc_ag_vextent_near(
 	 * If we couldn't get anything, give up.
 	 */
 	if (bno_cur_lt == NULL && bno_cur_gt == NULL) {
+		if (!forced++) {
+			trace_xfs_alloc_near_busy(args);
+			xfs_log_force(args->mp, XFS_LOG_SYNC);
+			goto restart;
+		}
+
 		trace_xfs_alloc_size_neither(args);
 		args->agbno = NULLAGBLOCK;
 		return 0;
@@ -1107,12 +1121,13 @@ xfs_alloc_ag_vextent_near(
 		return 0;
 	}
 	rlen = args->len;
-	(void)xfs_alloc_compute_diff(args->agbno, rlen, args->alignment, ltbno,
-		ltlen, &ltnew);
+	(void)xfs_alloc_compute_diff(args->agbno, rlen, args->alignment,
+				     ltbnoa, ltlena, &ltnew);
 	ASSERT(ltnew >= ltbno);
-	ASSERT(ltnew + rlen <= ltbno + ltlen);
+	ASSERT(ltnew + rlen <= ltbnoa + ltlena);
 	ASSERT(ltnew + rlen <= be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
 	args->agbno = ltnew;
+
 	if ((error = xfs_alloc_fixup_trees(cnt_cur, bno_cur_lt, ltbno, ltlen,
 			ltnew, rlen, XFSA_FIXUP_BNO_OK)))
 		goto error0;
@@ -1155,26 +1170,35 @@ xfs_alloc_ag_vextent_size(
 	int		i;		/* temp status variable */
 	xfs_agblock_t	rbno;		/* returned block number */
 	xfs_extlen_t	rlen;		/* length of returned extent */
+	int		forced = 0;
 
+restart:
 	/*
 	 * Allocate and initialize a cursor for the by-size btree.
 	 */
 	cnt_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
 		args->agno, XFS_BTNUM_CNT);
 	bno_cur = NULL;
+
 	/*
 	 * Look for an entry >= maxlen+alignment-1 blocks.
 	 */
 	if ((error = xfs_alloc_lookup_ge(cnt_cur, 0,
 			args->maxlen + args->alignment - 1, &i)))
 		goto error0;
+
 	/*
-	 * If none, then pick up the last entry in the tree unless the
-	 * tree is empty.
-	 */
-	if (!i) {
-		if ((error = xfs_alloc_ag_vextent_small(args, cnt_cur, &fbno,
-				&flen, &i)))
+	 * If none or we have busy extents that we cannot allocate from, then
+	 * we have to settle for a smaller extent. In the case that there are
+	 * no large extents, this will return the last entry in the tree unless
+	 * the tree is empty. In the case that there are only busy large
+	 * extents, this will return the largest small extent unless there
+	 * are no smaller extents available.
+	 */
+	if (!i || forced > 1) {
+		error = xfs_alloc_ag_vextent_small(args, cnt_cur,
+						   &fbno, &flen, &i);
+		if (error)
 			goto error0;
 		if (i == 0 || flen == 0) {
 			xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
@@ -1182,22 +1206,56 @@ xfs_alloc_ag_vextent_size(
 			return 0;
 		}
 		ASSERT(i == 1);
+		xfs_alloc_compute_aligned(args, fbno, flen, &rbno, &rlen);
+	} else {
+		/*
+		 * Search for a non-busy extent that is large enough.
+		 * If we are at low space, don't check, or if we fall of
+		 * the end of the btree, turn off the busy check and
+		 * restart.
+		 */
+		for (;;) {
+			error = xfs_alloc_get_rec(cnt_cur, &fbno, &flen, &i);
+			if (error)
+				goto error0;
+			XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
+
+			xfs_alloc_compute_aligned(args, fbno, flen,
+						  &rbno, &rlen);
+
+			if (rlen >= args->maxlen)
+				break;
+
+			error = xfs_btree_increment(cnt_cur, 0, &i);
+			if (error)
+				goto error0;
+			if (i == 0) {
+				/*
+				 * Our only valid extents must have been busy.
+				 * Make it unbusy by forcing the log out and
+				 * retrying. If we've been here before, forcing
+				 * the log isn't making the extents available,
+				 * which means they have probably been freed in
+				 * this transaction.  In that case, we have to
+				 * give up on them and we'll attempt a minlen
+				 * allocation the next time around.
+				 */
+				xfs_btree_del_cursor(cnt_cur,
+						     XFS_BTREE_NOERROR);
+				trace_xfs_alloc_size_busy(args);
+				if (!forced++)
+					xfs_log_force(args->mp, XFS_LOG_SYNC);
+				goto restart;
+			}
+		}
 	}
-	/*
-	 * There's a freespace as big as maxlen+alignment-1, get it.
-	 */
-	else {
-		if ((error = xfs_alloc_get_rec(cnt_cur, &fbno, &flen, &i)))
-			goto error0;
-		XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
-	}
+
 	/*
 	 * In the first case above, we got the last entry in the
 	 * by-size btree.  Now we check to see if the space hits maxlen
 	 * once aligned; if not, we search left for something better.
 	 * This can't happen in the second case above.
 	 */
-	xfs_alloc_compute_aligned(args, fbno, flen, &rbno, &rlen);
 	rlen = XFS_EXTLEN_MIN(args->maxlen, rlen);
 	XFS_WANT_CORRUPTED_GOTO(rlen == 0 ||
 			(rlen <= flen && rbno + rlen <= fbno + flen), error0);
@@ -1251,13 +1309,19 @@ xfs_alloc_ag_vextent_size(
 	 * Fix up the length.
 	 */
 	args->len = rlen;
-	xfs_alloc_fix_len(args);
-	if (rlen < args->minlen || !xfs_alloc_fix_minleft(args)) {
-		xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
-		trace_xfs_alloc_size_nominleft(args);
-		args->agbno = NULLAGBLOCK;
-		return 0;
+	if (rlen < args->minlen) {
+		if (!forced++) {
+			xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
+			trace_xfs_alloc_size_busy(args);
+			xfs_log_force(args->mp, XFS_LOG_SYNC);
+			goto restart;
+		}
+		goto out_nominleft;
 	}
+	xfs_alloc_fix_len(args);
+
+	if (!xfs_alloc_fix_minleft(args))
+		goto out_nominleft;
 	rlen = args->len;
 	XFS_WANT_CORRUPTED_GOTO(rlen <= flen, error0);
 	/*
@@ -1287,6 +1351,12 @@ error0:
 	if (bno_cur)
 		xfs_btree_del_cursor(bno_cur, XFS_BTREE_ERROR);
 	return error;
+
+out_nominleft:
+	xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
+	trace_xfs_alloc_size_nominleft(args);
+	args->agbno = NULLAGBLOCK;
+	return 0;
 }
 
 /*
@@ -2650,6 +2720,185 @@ xfs_alloc_busy_search(
 	return match;
 }
 
+/*
+ * For a given extent [fbno, flen], search the busy extent list to find a
+ * subset of the extent that is not busy.  If *rlen is smaller than
+ * args->minlen no suitable extent could be found, and the higher level
+ * code needs to force out the log and retry the allocation.
+ */
+STATIC void
+xfs_alloc_busy_trim(
+	struct xfs_alloc_arg	*args,
+	xfs_agblock_t		bno,
+	xfs_extlen_t		len,
+	xfs_agblock_t		*rbno,
+	xfs_extlen_t		*rlen)
+{
+	xfs_agblock_t		fbno = bno;
+	xfs_extlen_t		flen = len;
+	struct rb_node		*rbp;
+
+	ASSERT(flen > 0);
+
+	spin_lock(&args->pag->pagb_lock);
+	rbp = args->pag->pagb_tree.rb_node;
+	while (rbp && flen >= args->minlen) {
+		struct xfs_busy_extent *busyp =
+			rb_entry(rbp, struct xfs_busy_extent, rb_node);
+		xfs_agblock_t	fend = fbno + flen;
+		xfs_agblock_t	bbno = busyp->bno;
+		xfs_agblock_t	bend = bbno + busyp->length;
+
+		if (fend <= bbno) {
+			rbp = rbp->rb_left;
+			continue;
+		} else if (fbno >= bend) {
+			rbp = rbp->rb_right;
+			continue;
+		}
+
+		if (bbno <= fbno) {
+			/* start overlap */
+
+			/*
+			 * Case 1:
+			 *    bbno           bend
+			 *    +BBBBBBBBBBBBBBBBB+
+			 *        +---------+
+			 *        fbno   fend
+			 *
+			 * Case 2:
+			 *    bbno           bend
+			 *    +BBBBBBBBBBBBBBBBB+
+			 *    +-------------+
+			 *    fbno       fend
+			 *
+			 * Case 3:
+			 *    bbno           bend
+			 *    +BBBBBBBBBBBBBBBBB+
+			 *        +-------------+
+			 *        fbno       fend
+			 *
+			 * Case 4:
+			 *    bbno           bend
+			 *    +BBBBBBBBBBBBBBBBB+
+			 *    +-----------------+
+			 *    fbno           fend
+			 *
+			 * No unbusy region in extent, return failure.
+			 */
+			if (fend <= bend)
+				goto fail;
+
+			/*
+			 * Case 5:
+			 *    bbno           bend
+			 *    +BBBBBBBBBBBBBBBBB+
+			 *        +----------------------+
+			 *        fbno                fend
+			 *
+			 * Case 6:
+			 *    bbno           bend
+			 *    +BBBBBBBBBBBBBBBBB+
+			 *    +--------------------------+
+			 *    fbno                    fend
+			 *
+			 * Needs to be trimmed to:
+			 *                       +-------+
+			 *                       fbno fend
+			 */
+			fbno = bend;
+		} else if (bend >= fend) {
+			/* end overlap */
+
+			/*
+			 * Case 7:
+			 *             bbno           bend
+			 *             +BBBBBBBBBBBBBBBBB+
+			 *    +------------------+
+			 *    fbno            fend
+			 *
+			 * Case 8:
+			 *             bbno           bend
+			 *             +BBBBBBBBBBBBBBBBB+
+			 *    +--------------------------+
+			 *    fbno                    fend
+			 *
+			 * Needs to be trimmed to:
+			 *    +-------+
+			 *    fbno fend
+			 */
+			fend = bbno;
+		} else {
+			/* middle overlap */
+
+			/*
+			 * Case 9:
+			 *             bbno           bend
+			 *             +BBBBBBBBBBBBBBBBB+
+			 *    +-----------------------------------+
+			 *    fbno                             fend
+			 *
+			 * Can be trimmed to:
+			 *    +-------+        OR         +-------+
+			 *    fbno fend                   fbno fend
+			 *
+			 * Backward allocation leads to significant
+			 * fragmentation of directories, which degrades
+			 * directory performance, therefore we always want to
+			 * choose the option that produces forward allocation
+			 * patterns.
+			 * Preferring the lower bno extent will make the next
+			 * request use "fend" as the start of the next
+			 * allocation;  if the segment is no longer busy at
+			 * that point, we'll get a contiguous allocation, but
+			 * even if it is still busy, we will get a forward
+			 * allocation.
+			 * We try to avoid choosing the segment at "bend",
+			 * because that can lead to the next allocation
+			 * taking the segment at "fbno", which would be a
+			 * backward allocation.  We only use the segment at
+			 * "fbno" if it is much larger than the current
+			 * requested size, because in that case there's a
+			 * good chance subsequent allocations will be
+			 * contiguous.
+			 */
+			if (bbno - fbno >= args->maxlen) {
+				/* left candidate fits perfect */
+				fend = bbno;
+			} else if (fend - bend >= args->maxlen * 4) {
+				/* right candidate has enough free space */
+				fbno = bend;
+			} else if (bbno - fbno >= args->minlen) {
+				/* left candidate fits minimum requirement */
+				fend = bbno;
+			} else {
+				goto fail;
+			}
+		}
+
+		flen = fend - fbno;
+	}
+	spin_unlock(&args->pag->pagb_lock);
+
+	if (fbno != bno || flen != len) {
+		trace_xfs_alloc_busy_trim(args->mp, args->agno, bno, len,
+					  fbno, flen);
+	}
+	*rbno = fbno;
+	*rlen = flen;
+	return;
+fail:
+	/*
+	 * Return a zero extent length as failure indications.  All callers
+	 * re-check if the trimmed extent satisfies the minlen requirement.
+	 */
+	spin_unlock(&args->pag->pagb_lock);
+	trace_xfs_alloc_busy_trim(args->mp, args->agno, bno, len, fbno, 0);
+	*rbno = fbno;
+	*rlen = 0;
+}
+
 void
 xfs_alloc_busy_clear(
 	struct xfs_mount	*mp,
Index: xfs/fs/xfs/linux-2.6/xfs_trace.h
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_trace.h	2011-04-22 06:23:52.505828343 +0200
+++ xfs/fs/xfs/linux-2.6/xfs_trace.h	2011-04-22 06:23:56.162475200 +0200
@@ -1241,6 +1241,36 @@ TRACE_EVENT(xfs_alloc_busysearch,
 		  __print_symbolic(__entry->found, XFS_BUSY_STATES))
 );
 
+TRACE_EVENT(xfs_alloc_busy_trim,
+	TP_PROTO(struct xfs_mount *mp, xfs_agnumber_t agno,
+		 xfs_agblock_t agbno, xfs_extlen_t len,
+		 xfs_agblock_t tbno, xfs_extlen_t tlen),
+	TP_ARGS(mp, agno, agbno, len, tbno, tlen),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(xfs_agnumber_t, agno)
+		__field(xfs_agblock_t, agbno)
+		__field(xfs_extlen_t, len)
+		__field(xfs_agblock_t, tbno)
+		__field(xfs_extlen_t, tlen)
+	),
+	TP_fast_assign(
+		__entry->dev = mp->m_super->s_dev;
+		__entry->agno = agno;
+		__entry->agbno = agbno;
+		__entry->len = len;
+		__entry->tbno = tbno;
+		__entry->tlen = tlen;
+	),
+	TP_printk("dev %d:%d agno %u agbno %u len %u tbno %u tlen %u",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __entry->agno,
+		  __entry->agbno,
+		  __entry->len,
+		  __entry->tbno,
+		  __entry->tlen)
+);
+
 TRACE_EVENT(xfs_trans_commit_lsn,
 	TP_PROTO(struct xfs_trans *trans),
 	TP_ARGS(trans),
@@ -1433,11 +1463,14 @@ DEFINE_ALLOC_EVENT(xfs_alloc_near_first)
 DEFINE_ALLOC_EVENT(xfs_alloc_near_greater);
 DEFINE_ALLOC_EVENT(xfs_alloc_near_lesser);
 DEFINE_ALLOC_EVENT(xfs_alloc_near_error);
+DEFINE_ALLOC_EVENT(xfs_alloc_near_noentry);
+DEFINE_ALLOC_EVENT(xfs_alloc_near_busy);
 DEFINE_ALLOC_EVENT(xfs_alloc_size_neither);
 DEFINE_ALLOC_EVENT(xfs_alloc_size_noentry);
 DEFINE_ALLOC_EVENT(xfs_alloc_size_nominleft);
 DEFINE_ALLOC_EVENT(xfs_alloc_size_done);
 DEFINE_ALLOC_EVENT(xfs_alloc_size_error);
+DEFINE_ALLOC_EVENT(xfs_alloc_size_busy);
 DEFINE_ALLOC_EVENT(xfs_alloc_small_freelist);
 DEFINE_ALLOC_EVENT(xfs_alloc_small_notenough);
 DEFINE_ALLOC_EVENT(xfs_alloc_small_done);

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Re: [PATCH 2/4] xfs: do not immediately reuse busy extent ranges

[Dave Chinner]

On Sun, Apr 24, 2011 at 03:06:15PM -0400, Christoph Hellwig wrote:
> Every time we reallocate a busy extent, we cause a synchronous log force
> to occur to ensure the freeing transaction is on disk before we continue
> and use the newly allocated extent.  This is extremely sub-optimal as we
> have to mark every transaction with blocks that get reused as synchronous.
> 
> Instead of searching the busy extent list after deciding on the extent to
> allocate, check each candidate extent during the allocation decisions as
> to whether they are in the busy list.  If they are in the busy list, we
> trim the busy range out of the extent we have found and determine if that
> trimmed range is still OK for allocation. In many cases, this check can
> be incorporated into the allocation extent alignment code which already
> does trimming of the found extent before determining if it is a valid
> candidate for allocation.
> 
> Based on earlier patches from Dave Chinner.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Alex Elder <aelder@sgi.com>

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com

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[PATCH 3/4] xfs: exact busy extent tracking

[Christoph Hellwig]

[-- Attachment #1: xfs-better-busy-extent-tracking --]
[-- Type: text/plain, Size: 22759 bytes --]

Update the extent tree in case we have to reuse a busy extent, so that it
always is kept uptodate.  This is done by replacing the busy list searches
with a new xfs_alloc_busy_reuse helper, which updates the busy extent tree
in case of a reuse.  This allows us to allow reusing metadata extents
unconditionally, and thus avoid log forces especially for allocation btree
blocks.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>

Index: xfs/fs/xfs/xfs_alloc.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.c	2011-04-22 06:24:39.602239867 +0200
+++ xfs/fs/xfs/xfs_alloc.c	2011-04-22 06:26:42.898238581 +0200
@@ -1396,8 +1396,9 @@ xfs_alloc_ag_vextent_small(
 		if (error)
 			goto error0;
 		if (fbno != NULLAGBLOCK) {
-			if (xfs_alloc_busy_search(args->mp, args->agno, fbno, 1))
-				xfs_trans_set_sync(args->tp);
+			xfs_alloc_busy_reuse(args->mp, args->agno, fbno, 1,
+					     args->userdata);
+
 			if (args->userdata) {
 				xfs_buf_t	*bp;
 
@@ -2475,100 +2476,6 @@ error0:
 	return error;
 }
 
-
-/*
- * AG Busy list management
- * The busy list contains block ranges that have been freed but whose
- * transactions have not yet hit disk.  If any block listed in a busy
- * list is reused, the transaction that freed it must be forced to disk
- * before continuing to use the block.
- *
- * xfs_alloc_busy_insert - add to the per-ag busy list
- * xfs_alloc_busy_clear - remove an item from the per-ag busy list
- * xfs_alloc_busy_search - search for a busy extent
- */
-
-/*
- * Insert a new extent into the busy tree.
- *
- * The busy extent tree is indexed by the start block of the busy extent.
- * there can be multiple overlapping ranges in the busy extent tree but only
- * ever one entry at a given start block. The reason for this is that
- * multi-block extents can be freed, then smaller chunks of that extent
- * allocated and freed again before the first transaction commit is on disk.
- * If the exact same start block is freed a second time, we have to wait for
- * that busy extent to pass out of the tree before the new extent is inserted.
- * There are two main cases we have to handle here.
- *
- * The first case is a transaction that triggers a "free - allocate - free"
- * cycle. This can occur during btree manipulations as a btree block is freed
- * to the freelist, then allocated from the free list, then freed again. In
- * this case, the second extxpnet free is what triggers the duplicate and as
- * such the transaction IDs should match. Because the extent was allocated in
- * this transaction, the transaction must be marked as synchronous. This is
- * true for all cases where the free/alloc/free occurs in the one transaction,
- * hence the addition of the ASSERT(tp->t_flags & XFS_TRANS_SYNC) to this case.
- * This serves to catch violations of the second case quite effectively.
- *
- * The second case is where the free/alloc/free occur in different
- * transactions. In this case, the thread freeing the extent the second time
- * can't mark the extent busy immediately because it is already tracked in a
- * transaction that may be committing.  When the log commit for the existing
- * busy extent completes, the busy extent will be removed from the tree. If we
- * allow the second busy insert to continue using that busy extent structure,
- * it can be freed before this transaction is safely in the log.  Hence our
- * only option in this case is to force the log to remove the existing busy
- * extent from the list before we insert the new one with the current
- * transaction ID.
- *
- * The problem we are trying to avoid in the free-alloc-free in separate
- * transactions is most easily described with a timeline:
- *
- *      Thread 1	Thread 2	Thread 3	xfslogd
- *	xact alloc
- *	free X
- *	mark busy
- *	commit xact
- *	free xact
- *			xact alloc
- *			alloc X
- *			busy search
- *			mark xact sync
- *			commit xact
- *			free xact
- *			force log
- *			checkpoint starts
- *			....
- *					xact alloc
- *					free X
- *					mark busy
- *					finds match
- *					*** KABOOM! ***
- *					....
- *							log IO completes
- *							unbusy X
- *			checkpoint completes
- *
- * By issuing a log force in thread 3 @ "KABOOM", the thread will block until
- * the checkpoint completes, and the busy extent it matched will have been
- * removed from the tree when it is woken. Hence it can then continue safely.
- *
- * However, to ensure this matching process is robust, we need to use the
- * transaction ID for identifying transaction, as delayed logging results in
- * the busy extent and transaction lifecycles being different. i.e. the busy
- * extent is active for a lot longer than the transaction.  Hence the
- * transaction structure can be freed and reallocated, then mark the same
- * extent busy again in the new transaction. In this case the new transaction
- * will have a different tid but can have the same address, and hence we need
- * to check against the tid.
- *
- * Future: for delayed logging, we could avoid the log force if the extent was
- * first freed in the current checkpoint sequence. This, however, requires the
- * ability to pin the current checkpoint in memory until this transaction
- * commits to ensure that both the original free and the current one combine
- * logically into the one checkpoint. If the checkpoint sequences are
- * different, however, we still need to wait on a log force.
- */
 void
 xfs_alloc_busy_insert(
 	struct xfs_trans	*tp,
@@ -2580,9 +2487,7 @@ xfs_alloc_busy_insert(
 	struct xfs_busy_extent	*busyp;
 	struct xfs_perag	*pag;
 	struct rb_node		**rbp;
-	struct rb_node		*parent;
-	int			match;
-
+	struct rb_node		*parent = NULL;
 
 	new = kmem_zalloc(sizeof(struct xfs_busy_extent), KM_MAYFAIL);
 	if (!new) {
@@ -2591,7 +2496,7 @@ xfs_alloc_busy_insert(
 		 * block, make this a synchronous transaction to insure that
 		 * the block is not reused before this transaction commits.
 		 */
-		trace_xfs_alloc_busy(tp, agno, bno, len, 1);
+		trace_xfs_alloc_busy_enomem(tp->t_mountp, agno, bno, len);
 		xfs_trans_set_sync(tp);
 		return;
 	}
@@ -2599,66 +2504,28 @@ xfs_alloc_busy_insert(
 	new->agno = agno;
 	new->bno = bno;
 	new->length = len;
-	new->tid = xfs_log_get_trans_ident(tp);
-
 	INIT_LIST_HEAD(&new->list);
 
 	/* trace before insert to be able to see failed inserts */
-	trace_xfs_alloc_busy(tp, agno, bno, len, 0);
+	trace_xfs_alloc_busy(tp->t_mountp, agno, bno, len);
 
 	pag = xfs_perag_get(tp->t_mountp, new->agno);
-restart:
 	spin_lock(&pag->pagb_lock);
 	rbp = &pag->pagb_tree.rb_node;
-	parent = NULL;
-	busyp = NULL;
-	match = 0;
-	while (*rbp && match >= 0) {
+	while (*rbp) {
 		parent = *rbp;
 		busyp = rb_entry(parent, struct xfs_busy_extent, rb_node);
 
 		if (new->bno < busyp->bno) {
-			/* may overlap, but exact start block is lower */
 			rbp = &(*rbp)->rb_left;
-			if (new->bno + new->length > busyp->bno)
-				match = busyp->tid == new->tid ? 1 : -1;
+			ASSERT(new->bno + new->length <= busyp->bno);
 		} else if (new->bno > busyp->bno) {
-			/* may overlap, but exact start block is higher */
 			rbp = &(*rbp)->rb_right;
-			if (bno < busyp->bno + busyp->length)
-				match = busyp->tid == new->tid ? 1 : -1;
+			ASSERT(bno >= busyp->bno + busyp->length);
 		} else {
-			match = busyp->tid == new->tid ? 1 : -1;
-			break;
+			ASSERT(0);
 		}
 	}
-	if (match < 0) {
-		/* overlap marked busy in different transaction */
-		spin_unlock(&pag->pagb_lock);
-		xfs_log_force(tp->t_mountp, XFS_LOG_SYNC);
-		goto restart;
-	}
-	if (match > 0) {
-		/*
-		 * overlap marked busy in same transaction. Update if exact
-		 * start block match, otherwise combine the busy extents into
-		 * a single range.
-		 */
-		if (busyp->bno == new->bno) {
-			busyp->length = max(busyp->length, new->length);
-			spin_unlock(&pag->pagb_lock);
-			ASSERT(tp->t_flags & XFS_TRANS_SYNC);
-			xfs_perag_put(pag);
-			kmem_free(new);
-			return;
-		}
-		rb_erase(&busyp->rb_node, &pag->pagb_tree);
-		new->length = max(busyp->bno + busyp->length,
-					new->bno + new->length) -
-				min(busyp->bno, new->bno);
-		new->bno = min(busyp->bno, new->bno);
-	} else
-		busyp = NULL;
 
 	rb_link_node(&new->rb_node, parent, rbp);
 	rb_insert_color(&new->rb_node, &pag->pagb_tree);
@@ -2666,7 +2533,6 @@ restart:
 	list_add(&new->list, &tp->t_busy);
 	spin_unlock(&pag->pagb_lock);
 	xfs_perag_put(pag);
-	kmem_free(busyp);
 }
 
 /*
@@ -2715,12 +2581,196 @@ xfs_alloc_busy_search(
 		}
 	}
 	spin_unlock(&pag->pagb_lock);
-	trace_xfs_alloc_busysearch(mp, agno, bno, len, !!match);
 	xfs_perag_put(pag);
 	return match;
 }
 
 /*
+ * The found free extent [fbno, fend] overlaps part or all of the given busy
+ * extent.  If the overlap covers the beginning, the end, or all of the busy
+ * extent, the overlapping portion can be made unbusy and used for the
+ * allocation.  We can't split a busy extent because we can't modify a
+ * transaction/CIL context busy list, but we can update an entries block
+ * number or length.
+ *
+ * Returns true if the extent can safely be reused, or false if the search
+ * needs to be restarted.
+ */
+STATIC bool
+xfs_alloc_busy_update_extent(
+	struct xfs_mount	*mp,
+	struct xfs_perag	*pag,
+	struct xfs_busy_extent	*busyp,
+	xfs_agblock_t		fbno,
+	xfs_extlen_t		flen,
+	bool			userdata)
+{
+	xfs_agblock_t		fend = fbno + flen;
+	xfs_agblock_t		bbno = busyp->bno;
+	xfs_agblock_t		bend = bbno + busyp->length;
+
+	/*
+	 * If there is a busy extent overlapping a user allocation, we have
+	 * no choice but to force the log and retry the search.
+	 *
+	 * Fortunately this does not happen during normal operation, but
+	 * only if the filesystem is very low on space and has to dip into
+	 * the AGFL for normal allocations.
+	 */
+	if (userdata)
+		goto out_force_log;
+
+	if (bbno < fbno && bend > fend) {
+		/*
+		 * Case 1:
+		 *    bbno           bend
+		 *    +BBBBBBBBBBBBBBBBB+
+		 *        +---------+
+		 *        fbno   fend
+		 */
+
+		/*
+		 * We would have to split the busy extent to be able to track
+		 * it correct, which we cannot do because we would have to
+		 * modify the list of busy extents attached to the transaction
+		 * or CIL context, which is immutable.
+		 *
+		 * Force out the log to clear the busy extent and retry the
+		 * search.
+		 */
+		goto out_force_log;
+	} else if (bbno >= fbno && bend <= fend) {
+		/*
+		 * Case 2:
+		 *    bbno           bend
+		 *    +BBBBBBBBBBBBBBBBB+
+		 *    +-----------------+
+		 *    fbno           fend
+		 *
+		 * Case 3:
+		 *    bbno           bend
+		 *    +BBBBBBBBBBBBBBBBB+
+		 *    +--------------------------+
+		 *    fbno                    fend
+		 *
+		 * Case 4:
+		 *             bbno           bend
+		 *             +BBBBBBBBBBBBBBBBB+
+		 *    +--------------------------+
+		 *    fbno                    fend
+		 *
+		 * Case 5:
+		 *             bbno           bend
+		 *             +BBBBBBBBBBBBBBBBB+
+		 *    +-----------------------------------+
+		 *    fbno                             fend
+		 *
+		 */
+
+		/*
+		 * The busy extent is fully covered by the extent we are
+		 * allocating, and can simply be removed from the rbtree.
+		 * However we cannot remove it from the immutable list
+		 * tracking busy extents in the transaction or CIL context,
+		 * so set the length to zero to mark it invalid.
+		 *
+		 * We also need to restart the busy extent search from the
+		 * tree root, because erasing the node can rearrange the
+		 * tree topology.
+		 */
+		rb_erase(&busyp->rb_node, &pag->pagb_tree);
+		busyp->length = 0;
+		return false;
+	} else if (fend < bend) {
+		/*
+		 * Case 6:
+		 *              bbno           bend
+		 *             +BBBBBBBBBBBBBBBBB+
+		 *             +---------+
+		 *             fbno   fend
+		 *
+		 * Case 7:
+		 *             bbno           bend
+		 *             +BBBBBBBBBBBBBBBBB+
+		 *    +------------------+
+		 *    fbno            fend
+		 *
+		 */
+		busyp->bno = fend;
+	} else if (bbno < fbno) {
+		/*
+		 * Case 8:
+		 *    bbno           bend
+		 *    +BBBBBBBBBBBBBBBBB+
+		 *        +-------------+
+		 *        fbno       fend
+		 *
+		 * Case 9:
+		 *    bbno           bend
+		 *    +BBBBBBBBBBBBBBBBB+
+		 *        +----------------------+
+		 *        fbno                fend
+		 */
+		busyp->length = fbno - busyp->bno;
+	} else {
+		ASSERT(0);
+	}
+
+	trace_xfs_alloc_busy_reuse(mp, pag->pag_agno, fbno, flen);
+	return true;
+
+out_force_log:
+	spin_unlock(&pag->pagb_lock);
+	xfs_log_force(mp, XFS_LOG_SYNC);
+	trace_xfs_alloc_busy_force(mp, pag->pag_agno, fbno, flen);
+	spin_lock(&pag->pagb_lock);
+	return false;
+}
+
+
+/*
+ * For a given extent [fbno, flen], make sure we can reuse it safely.
+ */
+void
+xfs_alloc_busy_reuse(
+	struct xfs_mount	*mp,
+	xfs_agnumber_t		agno,
+	xfs_agblock_t		fbno,
+	xfs_extlen_t		flen,
+	bool			userdata)
+{
+	struct xfs_perag	*pag;
+	struct rb_node		*rbp;
+
+	ASSERT(flen > 0);
+
+	pag = xfs_perag_get(mp, agno);
+	spin_lock(&pag->pagb_lock);
+restart:
+	rbp = pag->pagb_tree.rb_node;
+	while (rbp) {
+		struct xfs_busy_extent *busyp =
+			rb_entry(rbp, struct xfs_busy_extent, rb_node);
+		xfs_agblock_t	bbno = busyp->bno;
+		xfs_agblock_t	bend = bbno + busyp->length;
+
+		if (fbno + flen <= bbno) {
+			rbp = rbp->rb_left;
+			continue;
+		} else if (fbno >= bend) {
+			rbp = rbp->rb_right;
+			continue;
+		}
+
+		if (!xfs_alloc_busy_update_extent(mp, pag, busyp, fbno, flen,
+						  userdata))
+			goto restart;
+	}
+	spin_unlock(&pag->pagb_lock);
+	xfs_perag_put(pag);
+}
+
+/*
  * For a given extent [fbno, flen], search the busy extent list to find a
  * subset of the extent that is not busy.  If *rlen is smaller than
  * args->minlen no suitable extent could be found, and the higher level
@@ -2734,13 +2784,16 @@ xfs_alloc_busy_trim(
 	xfs_agblock_t		*rbno,
 	xfs_extlen_t		*rlen)
 {
-	xfs_agblock_t		fbno = bno;
-	xfs_extlen_t		flen = len;
+	xfs_agblock_t		fbno;
+	xfs_extlen_t		flen;
 	struct rb_node		*rbp;
 
-	ASSERT(flen > 0);
+	ASSERT(len > 0);
 
 	spin_lock(&args->pag->pagb_lock);
+restart:
+	fbno = bno;
+	flen = len;
 	rbp = args->pag->pagb_tree.rb_node;
 	while (rbp && flen >= args->minlen) {
 		struct xfs_busy_extent *busyp =
@@ -2757,6 +2810,18 @@ xfs_alloc_busy_trim(
 			continue;
 		}
 
+		/*
+		 * If this is a metadata allocation, try to reuse the busy
+		 * extent instead of trimming the allocation.
+		 */
+		if (!args->userdata) {
+			if (!xfs_alloc_busy_update_extent(args->mp, args->pag,
+							  busyp, fbno, flen,
+							  false))
+				goto restart;
+			continue;
+		}
+
 		if (bbno <= fbno) {
 			/* start overlap */
 
@@ -2906,17 +2971,15 @@ xfs_alloc_busy_clear(
 {
 	struct xfs_perag	*pag;
 
-	trace_xfs_alloc_unbusy(mp, busyp->agno, busyp->bno,
-						busyp->length);
-
-	ASSERT(xfs_alloc_busy_search(mp, busyp->agno, busyp->bno,
-						busyp->length) == 1);
-
 	list_del_init(&busyp->list);
 
 	pag = xfs_perag_get(mp, busyp->agno);
 	spin_lock(&pag->pagb_lock);
-	rb_erase(&busyp->rb_node, &pag->pagb_tree);
+	if (busyp->length) {
+		trace_xfs_alloc_busy_clear(mp, busyp->agno, busyp->bno,
+						busyp->length);
+		rb_erase(&busyp->rb_node, &pag->pagb_tree);
+	}
 	spin_unlock(&pag->pagb_lock);
 	xfs_perag_put(pag);
 
Index: xfs/fs/xfs/xfs_alloc.h
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.h	2011-04-22 06:23:21.579329219 +0200
+++ xfs/fs/xfs/xfs_alloc.h	2011-04-22 06:26:42.898238581 +0200
@@ -145,6 +145,10 @@ xfs_alloc_busy_clear(struct xfs_mount *m
 int
 xfs_alloc_busy_search(struct xfs_mount *mp, xfs_agnumber_t agno,
 	xfs_agblock_t bno, xfs_extlen_t len);
+
+void
+xfs_alloc_busy_reuse(struct xfs_mount *mp, xfs_agnumber_t agno,
+	xfs_agblock_t fbno, xfs_extlen_t flen, bool userdata);
 #endif	/* __KERNEL__ */
 
 /*
Index: xfs/fs/xfs/xfs_alloc_btree.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc_btree.c	2011-04-22 06:23:21.592662481 +0200
+++ xfs/fs/xfs/xfs_alloc_btree.c	2011-04-22 06:26:42.918238473 +0200
@@ -94,8 +94,8 @@ xfs_allocbt_alloc_block(
 		*stat = 0;
 		return 0;
 	}
-	if (xfs_alloc_busy_search(cur->bc_mp, cur->bc_private.a.agno, bno, 1))
-		xfs_trans_set_sync(cur->bc_tp);
+
+	xfs_alloc_busy_reuse(cur->bc_mp, cur->bc_private.a.agno, bno, 1, false);
 
 	xfs_trans_agbtree_delta(cur->bc_tp, 1);
 	new->s = cpu_to_be32(bno);
@@ -120,17 +120,6 @@ xfs_allocbt_free_block(
 	if (error)
 		return error;
 
-	/*
-	 * Since blocks move to the free list without the coordination used in
-	 * xfs_bmap_finish, we can't allow block to be available for
-	 * reallocation and non-transaction writing (user data) until we know
-	 * that the transaction that moved it to the free list is permanently
-	 * on disk. We track the blocks by declaring these blocks as "busy";
-	 * the busy list is maintained on a per-ag basis and each transaction
-	 * records which entries should be removed when the iclog commits to
-	 * disk. If a busy block is allocated, the iclog is pushed up to the
-	 * LSN that freed the block.
-	 */
 	xfs_alloc_busy_insert(cur->bc_tp, be32_to_cpu(agf->agf_seqno), bno, 1);
 	xfs_trans_agbtree_delta(cur->bc_tp, -1);
 	return 0;
Index: xfs/fs/xfs/xfs_ag.h
===================================================================
--- xfs.orig/fs/xfs/xfs_ag.h	2011-04-22 06:23:21.609329056 +0200
+++ xfs/fs/xfs/xfs_ag.h	2011-04-22 06:26:42.921571788 +0200
@@ -187,7 +187,6 @@ struct xfs_busy_extent {
 	xfs_agnumber_t	agno;
 	xfs_agblock_t	bno;
 	xfs_extlen_t	length;
-	xlog_tid_t	tid;		/* transaction that created this */
 };
 
 /*
Index: xfs/fs/xfs/xfs_log.c
===================================================================
--- xfs.orig/fs/xfs/xfs_log.c	2011-04-22 06:23:21.625995634 +0200
+++ xfs/fs/xfs/xfs_log.c	2011-04-22 06:26:42.941571681 +0200
@@ -3248,13 +3248,6 @@ xfs_log_ticket_get(
 	return ticket;
 }
 
-xlog_tid_t
-xfs_log_get_trans_ident(
-	struct xfs_trans	*tp)
-{
-	return tp->t_ticket->t_tid;
-}
-
 /*
  * Allocate and initialise a new log ticket.
  */
Index: xfs/fs/xfs/xfs_log.h
===================================================================
--- xfs.orig/fs/xfs/xfs_log.h	2011-04-22 06:23:21.639328894 +0200
+++ xfs/fs/xfs/xfs_log.h	2011-04-22 06:26:42.951571626 +0200
@@ -189,8 +189,6 @@ void	  xlog_iodone(struct xfs_buf *);
 struct xlog_ticket *xfs_log_ticket_get(struct xlog_ticket *ticket);
 void	  xfs_log_ticket_put(struct xlog_ticket *ticket);
 
-xlog_tid_t xfs_log_get_trans_ident(struct xfs_trans *tp);
-
 void	xfs_log_commit_cil(struct xfs_mount *mp, struct xfs_trans *tp,
 				struct xfs_log_vec *log_vector,
 				xfs_lsn_t *commit_lsn, int flags);
Index: xfs/fs/xfs/xfs_log_priv.h
===================================================================
--- xfs.orig/fs/xfs/xfs_log_priv.h	2011-04-22 06:23:21.655995472 +0200
+++ xfs/fs/xfs/xfs_log_priv.h	2011-04-22 06:26:42.991571408 +0200
@@ -146,6 +146,8 @@ static inline uint xlog_get_client_id(__
 					   shutdown */
 #define XLOG_TAIL_WARN		0x10	/* log tail verify warning issued */
 
+typedef __uint32_t xlog_tid_t;
+
 #ifdef __KERNEL__
 /*
  * Below are states for covering allocation transactions.
Index: xfs/fs/xfs/xfs_types.h
===================================================================
--- xfs.orig/fs/xfs/xfs_types.h	2011-04-22 06:23:21.669328732 +0200
+++ xfs/fs/xfs/xfs_types.h	2011-04-22 06:26:42.991571408 +0200
@@ -73,8 +73,6 @@ typedef	__int32_t	xfs_tid_t;	/* transact
 typedef	__uint32_t	xfs_dablk_t;	/* dir/attr block number (in file) */
 typedef	__uint32_t	xfs_dahash_t;	/* dir/attr hash value */
 
-typedef __uint32_t	xlog_tid_t;	/* transaction ID type */
-
 /*
  * These types are 64 bits on disk but are either 32 or 64 bits in memory.
  * Disk based types:
Index: xfs/fs/xfs/linux-2.6/xfs_trace.h
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_trace.h	2011-04-22 06:23:56.162475200 +0200
+++ xfs/fs/xfs/linux-2.6/xfs_trace.h	2011-04-22 06:26:43.008237986 +0200
@@ -1151,44 +1151,7 @@ TRACE_EVENT(xfs_bunmap,
 
 );
 
-#define XFS_BUSY_SYNC \
-	{ 0,	"async" }, \
-	{ 1,	"sync" }
-
-TRACE_EVENT(xfs_alloc_busy,
-	TP_PROTO(struct xfs_trans *trans, xfs_agnumber_t agno,
-		 xfs_agblock_t agbno, xfs_extlen_t len, int sync),
-	TP_ARGS(trans, agno, agbno, len, sync),
-	TP_STRUCT__entry(
-		__field(dev_t, dev)
-		__field(struct xfs_trans *, tp)
-		__field(int, tid)
-		__field(xfs_agnumber_t, agno)
-		__field(xfs_agblock_t, agbno)
-		__field(xfs_extlen_t, len)
-		__field(int, sync)
-	),
-	TP_fast_assign(
-		__entry->dev = trans->t_mountp->m_super->s_dev;
-		__entry->tp = trans;
-		__entry->tid = trans->t_ticket->t_tid;
-		__entry->agno = agno;
-		__entry->agbno = agbno;
-		__entry->len = len;
-		__entry->sync = sync;
-	),
-	TP_printk("dev %d:%d trans 0x%p tid 0x%x agno %u agbno %u len %u %s",
-		  MAJOR(__entry->dev), MINOR(__entry->dev),
-		  __entry->tp,
-		  __entry->tid,
-		  __entry->agno,
-		  __entry->agbno,
-		  __entry->len,
-		  __print_symbolic(__entry->sync, XFS_BUSY_SYNC))
-
-);
-
-TRACE_EVENT(xfs_alloc_unbusy,
+DECLARE_EVENT_CLASS(xfs_busy_class,
 	TP_PROTO(struct xfs_mount *mp, xfs_agnumber_t agno,
 		 xfs_agblock_t agbno, xfs_extlen_t len),
 	TP_ARGS(mp, agno, agbno, len),
@@ -1210,36 +1173,16 @@ TRACE_EVENT(xfs_alloc_unbusy,
 		  __entry->agbno,
 		  __entry->len)
 );
-
-#define XFS_BUSY_STATES \
-	{ 0,	"missing" }, \
-	{ 1,	"found" }
-
-TRACE_EVENT(xfs_alloc_busysearch,
-	TP_PROTO(struct xfs_mount *mp, xfs_agnumber_t agno,
-		 xfs_agblock_t agbno, xfs_extlen_t len, int found),
-	TP_ARGS(mp, agno, agbno, len, found),
-	TP_STRUCT__entry(
-		__field(dev_t, dev)
-		__field(xfs_agnumber_t, agno)
-		__field(xfs_agblock_t, agbno)
-		__field(xfs_extlen_t, len)
-		__field(int, found)
-	),
-	TP_fast_assign(
-		__entry->dev = mp->m_super->s_dev;
-		__entry->agno = agno;
-		__entry->agbno = agbno;
-		__entry->len = len;
-		__entry->found = found;
-	),
-	TP_printk("dev %d:%d agno %u agbno %u len %u %s",
-		  MAJOR(__entry->dev), MINOR(__entry->dev),
-		  __entry->agno,
-		  __entry->agbno,
-		  __entry->len,
-		  __print_symbolic(__entry->found, XFS_BUSY_STATES))
-);
+#define DEFINE_BUSY_EVENT(name) \
+DEFINE_EVENT(xfs_busy_class, name, \
+	TP_PROTO(struct xfs_mount *mp, xfs_agnumber_t agno, \
+		 xfs_agblock_t agbno, xfs_extlen_t len), \
+	TP_ARGS(mp, agno, agbno, len))
+DEFINE_BUSY_EVENT(xfs_alloc_busy);
+DEFINE_BUSY_EVENT(xfs_alloc_busy_enomem);
+DEFINE_BUSY_EVENT(xfs_alloc_busy_force);
+DEFINE_BUSY_EVENT(xfs_alloc_busy_reuse);
+DEFINE_BUSY_EVENT(xfs_alloc_busy_clear);
 
 TRACE_EVENT(xfs_alloc_busy_trim,
 	TP_PROTO(struct xfs_mount *mp, xfs_agnumber_t agno,

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Re: [PATCH 3/4] xfs: exact busy extent tracking

[Dave Chinner]

On Sun, Apr 24, 2011 at 03:06:16PM -0400, Christoph Hellwig wrote:
> Update the extent tree in case we have to reuse a busy extent, so that it
> always is kept uptodate.  This is done by replacing the busy list searches
> with a new xfs_alloc_busy_reuse helper, which updates the busy extent tree
> in case of a reuse.  This allows us to allow reusing metadata extents
> unconditionally, and thus avoid log forces especially for allocation btree
> blocks.

I'd add one comment to this - that this returns to the old way of
clearing busy extents by issuing a sync log force with the AGF
locked. This can cause additional allocation latency, but should be
rare given the occurrence of of metadata->data reallocation.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Alex Elder <aelder@sgi.com>

Otherwise,

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com

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http://oss.sgi.com/mailman/listinfo/xfs

[PATCH 4/4] xfs: reduce the number of pagb_lock roundtrips in xfs_alloc_clear_busy

[Christoph Hellwig]

[-- Attachment #1: xfs-reduce-pagb_lock-roundtrips --]
[-- Type: text/plain, Size: 5419 bytes --]

Instead of finding the per-ag and then taking and releasing the pagb_lock
for every single busy extent completed sort the list of busy extents and
only switch betweens AGs where nessecary.  This becomes especially important
with the online discard support which will hit this lock more often.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: xfs/fs/xfs/xfs_alloc.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.c	2011-04-15 09:47:49.034982545 +0200
+++ xfs/fs/xfs/xfs_alloc.c	2011-04-15 11:56:01.049977986 +0200
@@ -2968,24 +2968,60 @@ fail:
 	*rlen = 0;
 }
 
-void
-xfs_alloc_busy_clear(
+static void
+xfs_alloc_busy_clear_one(
 	struct xfs_mount	*mp,
+	struct xfs_perag	*pag,
 	struct xfs_busy_extent	*busyp)
 {
-	struct xfs_perag	*pag;
-
-	list_del_init(&busyp->list);
-
-	pag = xfs_perag_get(mp, busyp->agno);
-	spin_lock(&pag->pagb_lock);
 	if (busyp->length) {
 		trace_xfs_alloc_busy_clear(mp, busyp->agno, busyp->bno,
 						busyp->length);
 		rb_erase(&busyp->rb_node, &pag->pagb_tree);
 	}
-	spin_unlock(&pag->pagb_lock);
-	xfs_perag_put(pag);
 
+	list_del_init(&busyp->list);
 	kmem_free(busyp);
 }
+
+void
+xfs_alloc_busy_clear(
+	struct xfs_mount	*mp,
+	struct list_head	*list)
+{
+	struct xfs_busy_extent	*busyp, *n;
+	struct xfs_perag	*pag = NULL;
+	xfs_agnumber_t		agno = NULLAGNUMBER;
+
+	list_for_each_entry_safe(busyp, n, list, list) {
+		if (busyp->agno != agno) {
+			if (pag) {
+				spin_unlock(&pag->pagb_lock);
+				xfs_perag_put(pag);
+			}
+			pag = xfs_perag_get(mp, busyp->agno);
+			spin_lock(&pag->pagb_lock);
+			agno = busyp->agno;
+		}
+
+		xfs_alloc_busy_clear_one(mp, pag, busyp);
+	}
+
+	if (pag) {
+		spin_unlock(&pag->pagb_lock);
+		xfs_perag_put(pag);
+	}
+}
+
+/*
+ * Callback for list_sort to sort busy extents by the AG they reside in.
+ */
+int
+xfs_busy_extent_ag_cmp(
+	void			*priv,
+	struct list_head	*a,
+	struct list_head	*b)
+{
+	return container_of(a, struct xfs_busy_extent, list)->agno -
+		container_of(b, struct xfs_busy_extent, list)->agno;
+}
Index: xfs/fs/xfs/xfs_alloc.h
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.h	2011-04-15 09:47:49.041649176 +0200
+++ xfs/fs/xfs/xfs_alloc.h	2011-04-15 11:56:05.426620946 +0200
@@ -140,7 +140,7 @@ xfs_alloc_busy_insert(struct xfs_trans *
 	xfs_agblock_t bno, xfs_extlen_t len);
 
 void
-xfs_alloc_busy_clear(struct xfs_mount *mp, struct xfs_busy_extent *busyp);
+xfs_alloc_busy_clear(struct xfs_mount *mp, struct list_head *list);
 
 int
 xfs_alloc_busy_search(struct xfs_mount *mp, xfs_agnumber_t agno,
@@ -149,6 +149,15 @@ xfs_alloc_busy_search(struct xfs_mount *
 void
 xfs_alloc_busy_reuse(struct xfs_mount *mp, xfs_agnumber_t agno,
 	xfs_agblock_t fbno, xfs_extlen_t flen, bool userdata);
+
+int
+xfs_busy_extent_ag_cmp(void *priv, struct list_head *a, struct list_head *b);
+
+static inline void xfs_alloc_busy_sort(struct list_head *list)
+{
+	list_sort(NULL, list, xfs_busy_extent_ag_cmp);
+}
+
 #endif	/* __KERNEL__ */
 
 /*
Index: xfs/fs/xfs/xfs_log_cil.c
===================================================================
--- xfs.orig/fs/xfs/xfs_log_cil.c	2011-04-15 09:47:49.048315806 +0200
+++ xfs/fs/xfs/xfs_log_cil.c	2011-04-15 11:53:09.594240178 +0200
@@ -361,13 +361,12 @@ xlog_cil_committed(
 	int	abort)
 {
 	struct xfs_cil_ctx	*ctx = args;
-	struct xfs_busy_extent	*busyp, *n;
 
 	xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
 					ctx->start_lsn, abort);
 
-	list_for_each_entry_safe(busyp, n, &ctx->busy_extents, list)
-		xfs_alloc_busy_clear(ctx->cil->xc_log->l_mp, busyp);
+	xfs_alloc_busy_sort(&ctx->busy_extents);
+	xfs_alloc_busy_clear(ctx->cil->xc_log->l_mp, &ctx->busy_extents);
 
 	spin_lock(&ctx->cil->xc_cil_lock);
 	list_del(&ctx->committing);
Index: xfs/fs/xfs/xfs_trans.c
===================================================================
--- xfs.orig/fs/xfs/xfs_trans.c	2011-04-15 09:47:49.054982436 +0200
+++ xfs/fs/xfs/xfs_trans.c	2011-04-15 11:53:24.300827172 +0200
@@ -608,10 +608,8 @@ STATIC void
 xfs_trans_free(
 	struct xfs_trans	*tp)
 {
-	struct xfs_busy_extent	*busyp, *n;
-
-	list_for_each_entry_safe(busyp, n, &tp->t_busy, list)
-		xfs_alloc_busy_clear(tp->t_mountp, busyp);
+	xfs_alloc_busy_sort(&tp->t_busy);
+	xfs_alloc_busy_clear(tp->t_mountp, &tp->t_busy);
 
 	atomic_dec(&tp->t_mountp->m_active_trans);
 	xfs_trans_free_dqinfo(tp);
Index: xfs/fs/xfs/linux-2.6/xfs_buf.c
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_buf.c	2011-04-15 11:53:44.480717849 +0200
+++ xfs/fs/xfs/linux-2.6/xfs_buf.c	2011-04-15 11:53:47.934032472 +0200
@@ -33,7 +33,6 @@
 #include <linux/migrate.h>
 #include <linux/backing-dev.h>
 #include <linux/freezer.h>
-#include <linux/list_sort.h>
 
 #include "xfs_sb.h"
 #include "xfs_inum.h"
Index: xfs/fs/xfs/linux-2.6/xfs_linux.h
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_linux.h	2011-04-15 11:53:44.500717739 +0200
+++ xfs/fs/xfs/linux-2.6/xfs_linux.h	2011-04-15 11:53:53.234003761 +0200
@@ -70,6 +70,7 @@
 #include <linux/ctype.h>
 #include <linux/writeback.h>
 #include <linux/capability.h>
+#include <linux/list_sort.h>
 
 #include <asm/page.h>
 #include <asm/div64.h>

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Re: [PATCH 4/4] xfs: reduce the number of pagb_lock roundtrips in xfs_alloc_clear_busy

[Alex Elder]

On Sun, 2011-04-24 at 15:06 -0400, Christoph Hellwig wrote:
> Instead of finding the per-ag and then taking and releasing the pagb_lock
> for every single busy extent completed sort the list of busy extents and
> only switch betweens AGs where nessecary.  This becomes especially important
> with the online discard support which will hit this lock more often.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

I said this looked good before, but since you haven't
indicated that here yet, I'll make one more comment.

Both places that call (the new) xfs_alloc_busy_clear()
precede the call with a call to xfs_alloc_busy_sort().
Considering that, and the fact that xfs_alloc_busy_clear()
depends on the list being sorted for correct (or at least
efficient) operation, I think you should just embed the
list_sort() call in xfs_alloc_busy_clear().

There would then be no real need to define the
xfs_alloc_busy_sort() helper (just call list_sort()
directly), and you can move the definition of
xfs_busy_extent_ag_cmp() up in the file and give
it private scope.

Perhaps you have other plans that make the model you
have here more appropriate though.  Let me know
if you intend to re-submit, otherwise I'll just take
this version.

Either way, this looks good to me.  I have been
testing with these patches.  I'll wait another day
to give others a chance to review, but I'll plan
to incorporate this tomorrow.

Reviewed-by: Alex Elder <aelder@sgi.com>


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Re: [PATCH 4/4] xfs: reduce the number of pagb_lock roundtrips in xfs_alloc_clear_busy

[Christoph Hellwig]

On Wed, Apr 27, 2011 at 11:56:21AM -0500, Alex Elder wrote:
> Perhaps you have other plans that make the model you
> have here more appropriate though.  Let me know
> if you intend to re-submit, otherwise I'll just take
> this version.

The discard support will call xfs_alloc_busy_clear twice for
each list, once to clear all items that don't need discarding,
and a second pass once we're done with the discards.  Keeping
the sorting separate just seems cleaner at that point.

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Re: [PATCH 4/4] xfs: reduce the number of pagb_lock roundtrips in xfs_alloc_clear_busy

[Dave Chinner]

On Wed, Apr 27, 2011 at 11:56:21AM -0500, Alex Elder wrote:
> On Sun, 2011-04-24 at 15:06 -0400, Christoph Hellwig wrote:
> > Instead of finding the per-ag and then taking and releasing the pagb_lock
> > for every single busy extent completed sort the list of busy extents and
> > only switch betweens AGs where nessecary.  This becomes especially important
> > with the online discard support which will hit this lock more often.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> I said this looked good before, but since you haven't
> indicated that here yet, I'll make one more comment.
> 
> Both places that call (the new) xfs_alloc_busy_clear()
> precede the call with a call to xfs_alloc_busy_sort().
> Considering that, and the fact that xfs_alloc_busy_clear()
> depends on the list being sorted for correct (or at least
> efficient) operation, I think you should just embed the
> list_sort() call in xfs_alloc_busy_clear().
> 
> There would then be no real need to define the
> xfs_alloc_busy_sort() helper (just call list_sort()
> directly), and you can move the definition of
> xfs_busy_extent_ag_cmp() up in the file and give
> it private scope.

I agree with this - sorting the list externally just seems to
complicate the API and means callers need to remember to sort the
list first...

Otherwise,

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com

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[PATCH 0/4] improved busy extent handling V4

[Christoph Hellwig]

This series optimizes how XFS deals with busy extents.  It starts to
track them exactly, and allows reuses where possible (metadata to metadata)
or else tries to avoid busy extents during allocations.  This means
we don't have a single log force due to busy extents during either
xfstests, compilebench or postmark on my testsystem, which can easily
be tracked using the new tracepoints added in the last patch.

Changes from V3:
 - address review comments from Alex in patch 2
 - add a new patch to reduce pagb_lock roundtrips
Changes from V2:
 - remove the bmapi userdata tracking now that is unused
 - restructure the busy extent reuse code to make it more suitable
   for the discard support
 - reshuffle the patch boundaries

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[PATCH 4/4] xfs: reduce the number of pagb_lock roundtrips in xfs_alloc_clear_busy

[Christoph Hellwig]

[-- Attachment #1: xfs-reduce-pagb_lock-roundtrips --]
[-- Type: text/plain, Size: 5418 bytes --]

Instead of finding the per-ag and then taking and releasing the pagb_lock
for every single busy extent completed sort the list of busy extents and
only switch betweens AGs where nessecary.  This becomes especially important
with the online discard support which will hit this lock more often.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Index: xfs/fs/xfs/xfs_alloc.c
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.c	2011-04-15 09:47:49.034982545 +0200
+++ xfs/fs/xfs/xfs_alloc.c	2011-04-15 11:56:01.049977986 +0200
@@ -2968,24 +2968,60 @@ fail:
 	*rlen = 0;
 }
 
-void
-xfs_alloc_busy_clear(
+static void
+xfs_alloc_busy_clear_one(
 	struct xfs_mount	*mp,
+	struct xfs_perag	*pag,
 	struct xfs_busy_extent	*busyp)
 {
-	struct xfs_perag	*pag;
-
-	list_del_init(&busyp->list);
-
-	pag = xfs_perag_get(mp, busyp->agno);
-	spin_lock(&pag->pagb_lock);
 	if (busyp->length) {
 		trace_xfs_alloc_busy_clear(mp, busyp->agno, busyp->bno,
 						busyp->length);
 		rb_erase(&busyp->rb_node, &pag->pagb_tree);
 	}
-	spin_unlock(&pag->pagb_lock);
-	xfs_perag_put(pag);
 
+	list_del_init(&busyp->list);
 	kmem_free(busyp);
 }
+
+void
+xfs_alloc_busy_clear(
+	struct xfs_mount	*mp,
+	struct list_head	*list)
+{
+	struct xfs_busy_extent	*busyp, *n;
+	struct xfs_perag	*pag = NULL;
+	xfs_agnumber_t		agno = NULLAGNUMBER;
+
+	list_for_each_entry_safe(busyp, n, list, list) {
+		if (busyp->agno != agno) {
+			if (pag) {
+				spin_unlock(&pag->pagb_lock);
+				xfs_perag_put(pag);
+			}
+			pag = xfs_perag_get(mp, busyp->agno);
+			spin_lock(&pag->pagb_lock);
+			agno = busyp->agno;
+		}
+
+		xfs_alloc_busy_clear_one(mp, pag, busyp);
+	}
+
+	if (pag) {
+		spin_unlock(&pag->pagb_lock);
+		xfs_perag_put(pag);
+	}
+}
+
+/*
+ * Callback for list_sort to sort busy extents by the AG they reside in.
+ */
+int
+xfs_busy_extent_ag_cmp(
+	void			*priv,
+	struct list_head	*a,
+	struct list_head	*b)
+{
+	return container_of(a, struct xfs_busy_extent, list)->agno -
+		container_of(b, struct xfs_busy_extent, list)->agno;
+}
Index: xfs/fs/xfs/xfs_alloc.h
===================================================================
--- xfs.orig/fs/xfs/xfs_alloc.h	2011-04-15 09:47:49.041649176 +0200
+++ xfs/fs/xfs/xfs_alloc.h	2011-04-15 11:56:05.426620946 +0200
@@ -140,7 +140,7 @@ xfs_alloc_busy_insert(struct xfs_trans *
 	xfs_agblock_t bno, xfs_extlen_t len);
 
 void
-xfs_alloc_busy_clear(struct xfs_mount *mp, struct xfs_busy_extent *busyp);
+xfs_alloc_busy_clear(struct xfs_mount *mp, struct list_head *list);
 
 int
 xfs_alloc_busy_search(struct xfs_mount *mp, xfs_agnumber_t agno,
@@ -149,6 +149,15 @@ xfs_alloc_busy_search(struct xfs_mount *
 void
 xfs_alloc_busy_reuse(struct xfs_mount *mp, xfs_agnumber_t agno,
 	xfs_agblock_t fbno, xfs_extlen_t flen, bool userdata);
+
+int
+xfs_busy_extent_ag_cmp(void *priv, struct list_head *a, struct list_head *b);
+
+static inline void xfs_alloc_busy_sort(struct list_head *list)
+{
+	list_sort(NULL, list, xfs_busy_extent_ag_cmp);
+}
+
 #endif	/* __KERNEL__ */
 
 /*
Index: xfs/fs/xfs/xfs_log_cil.c
===================================================================
--- xfs.orig/fs/xfs/xfs_log_cil.c	2011-04-15 09:47:49.048315806 +0200
+++ xfs/fs/xfs/xfs_log_cil.c	2011-04-15 11:53:09.594240178 +0200
@@ -361,13 +361,12 @@ xlog_cil_committed(
 	int	abort)
 {
 	struct xfs_cil_ctx	*ctx = args;
-	struct xfs_busy_extent	*busyp, *n;
 
 	xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
 					ctx->start_lsn, abort);
 
-	list_for_each_entry_safe(busyp, n, &ctx->busy_extents, list)
-		xfs_alloc_busy_clear(ctx->cil->xc_log->l_mp, busyp);
+	xfs_alloc_busy_sort(&ctx->busy_extents);
+	xfs_alloc_busy_clear(ctx->cil->xc_log->l_mp, &ctx->busy_extents);
 
 	spin_lock(&ctx->cil->xc_cil_lock);
 	list_del(&ctx->committing);
Index: xfs/fs/xfs/xfs_trans.c
===================================================================
--- xfs.orig/fs/xfs/xfs_trans.c	2011-04-15 09:47:49.054982436 +0200
+++ xfs/fs/xfs/xfs_trans.c	2011-04-15 11:53:24.300827172 +0200
@@ -608,10 +608,8 @@ STATIC void
 xfs_trans_free(
 	struct xfs_trans	*tp)
 {
-	struct xfs_busy_extent	*busyp, *n;
-
-	list_for_each_entry_safe(busyp, n, &tp->t_busy, list)
-		xfs_alloc_busy_clear(tp->t_mountp, busyp);
+	xfs_alloc_busy_sort(&tp->t_busy);
+	xfs_alloc_busy_clear(tp->t_mountp, &tp->t_busy);
 
 	atomic_dec(&tp->t_mountp->m_active_trans);
 	xfs_trans_free_dqinfo(tp);
Index: xfs/fs/xfs/linux-2.6/xfs_buf.c
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_buf.c	2011-04-15 11:53:44.480717849 +0200
+++ xfs/fs/xfs/linux-2.6/xfs_buf.c	2011-04-15 11:53:47.934032472 +0200
@@ -33,7 +33,6 @@
 #include <linux/migrate.h>
 #include <linux/backing-dev.h>
 #include <linux/freezer.h>
-#include <linux/list_sort.h>
 
 #include "xfs_sb.h"
 #include "xfs_inum.h"
Index: xfs/fs/xfs/linux-2.6/xfs_linux.h
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_linux.h	2011-04-15 11:53:44.500717739 +0200
+++ xfs/fs/xfs/linux-2.6/xfs_linux.h	2011-04-15 11:53:53.234003761 +0200
@@ -70,6 +70,7 @@
 #include <linux/ctype.h>
 #include <linux/writeback.h>
 #include <linux/capability.h>
+#include <linux/list_sort.h>
 
 #include <asm/page.h>
 #include <asm/div64.h>

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