xfs: xfs_alloc_fix_freelist() can use incore perag structures

At the moment, xfs_alloc_fix_freelist() uses a mix of per-ag based
access and agf buffer  based access to freelist and space usage
information. However, once the AGF buffer is locked inside this
function, it is guaranteed that both the in-memory and on-disk
values are identical. xfs_alloc_fix_freelist() doesn't modify the
values in the structures directly, so it is a read-only user of the
infomration, and hence can use the per-ag structure exclusively for
determining what it should do.

This opens up an avenue for cleaning up a lot of duplicated logic
whose only difference is the structure it gets the data from, and in
doing so removes a lot of needless byte swapping overhead when
fixing up the free list.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_alloc.c

@@ -1825,11 +1825,11 @@ xfs_alloc_compute_maxlevels(
 xfs_extlen_t
 xfs_alloc_longest_free_extent(
 	struct xfs_mount	*mp,
-	struct xfs_perag	*pag)
+	struct xfs_perag	*pag,
+	xfs_extlen_t		need)
 {
-	xfs_extlen_t		need, delta = 0;
+	xfs_extlen_t		delta = 0;
 
-	need = XFS_MIN_FREELIST_PAG(pag, mp);
 	if (need > pag->pagf_flcount)
 		delta = need - pag->pagf_flcount;
 
@@ -1848,10 +1848,8 @@ xfs_alloc_fix_freelist(
 	int		flags)	/* XFS_ALLOC_FLAG_... */
 {
 	xfs_buf_t	*agbp;	/* agf buffer pointer */
-	xfs_agf_t	*agf;	/* a.g. freespace structure pointer */
 	xfs_buf_t	*agflbp;/* agfl buffer pointer */
 	xfs_agblock_t	bno;	/* freelist block */
-	xfs_extlen_t	delta;	/* new blocks needed in freelist */
 	int		error;	/* error result code */
 	xfs_extlen_t	longest;/* longest extent in allocation group */
 	xfs_mount_t	*mp;	/* file system mount point structure */
@@ -1895,7 +1893,7 @@ xfs_alloc_fix_freelist(
 		 * total blocks, reject it.
 		 */
 		need = XFS_MIN_FREELIST_PAG(pag, mp);
-		longest = xfs_alloc_longest_free_extent(mp, pag);
+		longest = xfs_alloc_longest_free_extent(mp, pag, need);
 		if ((args->minlen + args->alignment + args->minalignslop - 1) >
 				longest ||
 		    ((int)(pag->pagf_freeblks + pag->pagf_flcount -
@@ -1922,47 +1920,42 @@ xfs_alloc_fix_freelist(
 			return 0;
 		}
 	}
-	/*
-	 * Figure out how many blocks we should have in the freelist.
-	 */
-	agf = XFS_BUF_TO_AGF(agbp);
-	need = XFS_MIN_FREELIST(agf, mp);
-	/*
-	 * If there isn't enough total or single-extent, reject it.
-	 */
+
+
+	/* If there isn't enough total space or single-extent, reject it. */
+	need = XFS_MIN_FREELIST_PAG(pag, mp);
 	if (!(flags & XFS_ALLOC_FLAG_FREEING)) {
-		delta = need > be32_to_cpu(agf->agf_flcount) ?
-			(need - be32_to_cpu(agf->agf_flcount)) : 0;
-		longest = be32_to_cpu(agf->agf_longest);
-		longest = (longest > delta) ? (longest - delta) :
-			(be32_to_cpu(agf->agf_flcount) > 0 || longest > 0);
+		longest = xfs_alloc_longest_free_extent(mp, pag, need);
 		if ((args->minlen + args->alignment + args->minalignslop - 1) >
 				longest ||
-		    ((int)(be32_to_cpu(agf->agf_freeblks) +
-		     be32_to_cpu(agf->agf_flcount) - need - args->total) <
-				(int)args->minleft)) {
+		    ((int)(pag->pagf_freeblks + pag->pagf_flcount -
+			   need - args->total) < (int)args->minleft)) {
 			xfs_trans_brelse(tp, agbp);
 			args->agbp = NULL;
 			return 0;
 		}
 	}
 	/*
 	 * Make the freelist shorter if it's too long.
+	 *
+	 * XXX (dgc): When we have lots of free space, does this buy us
+	 * anything other than extra overhead when we need to put more blocks
+	 * back on the free list? Maybe we should only do this when space is
+	 * getting low or the AGFL is more than half full?
 	 */
-	while (be32_to_cpu(agf->agf_flcount) > need) {
-		xfs_buf_t	*bp;
+	while (pag->pagf_flcount > need) {
+		struct xfs_buf	*bp;
 
 		error = xfs_alloc_get_freelist(tp, agbp, &bno, 0);
 		if (error)
 			return error;
-		if ((error = xfs_free_ag_extent(tp, agbp, args->agno, bno, 1, 1)))
+		error = xfs_free_ag_extent(tp, agbp, args->agno, bno, 1, 1);
+		if (error)
 			return error;
 		bp = xfs_btree_get_bufs(mp, tp, args->agno, bno, 0);
 		xfs_trans_binval(tp, bp);
 	}
-	/*
-	 * Initialize the args structure.
-	 */
+
 	memset(&targs, 0, sizeof(targs));
 	targs.tp = tp;
 	targs.mp = mp;
@@ -1971,18 +1964,18 @@ xfs_alloc_fix_freelist(
 	targs.alignment = targs.minlen = targs.prod = targs.isfl = 1;
 	targs.type = XFS_ALLOCTYPE_THIS_AG;
 	targs.pag = pag;
-	if ((error = xfs_alloc_read_agfl(mp, tp, targs.agno, &agflbp)))
+	error = xfs_alloc_read_agfl(mp, tp, targs.agno, &agflbp);
+	if (error)
 		return error;
-	/*
-	 * Make the freelist longer if it's too short.
-	 */
-	while (be32_to_cpu(agf->agf_flcount) < need) {
+
+	/* Make the freelist longer if it's too short. */
+	while (pag->pagf_flcount < need) {
 		targs.agbno = 0;
-		targs.maxlen = need - be32_to_cpu(agf->agf_flcount);
-		/*
-		 * Allocate as many blocks as possible at once.
-		 */
-		if ((error = xfs_alloc_ag_vextent(&targs))) {
+		targs.maxlen = need - pag->pagf_flcount;
+
+		/* Allocate as many blocks as possible at once. */
+		error = xfs_alloc_ag_vextent(&targs);
+		if (error) {
 			xfs_trans_brelse(tp, agflbp);
 			return error;
 		}

fs/xfs/libxfs/xfs_alloc.h

@@ -128,12 +128,8 @@ typedef struct xfs_alloc_arg {
 #define XFS_ALLOC_USERDATA		1	/* allocation is for user data*/
 #define XFS_ALLOC_INITIAL_USER_DATA	2	/* special case start of file */
 
-/*
- * Find the length of the longest extent in an AG.
- */
-xfs_extlen_t
-xfs_alloc_longest_free_extent(struct xfs_mount *mp,
-		struct xfs_perag *pag);
+xfs_extlen_t xfs_alloc_longest_free_extent(struct xfs_mount *mp,
+		struct xfs_perag *pag, xfs_extlen_t need);
 
 /*
  * Compute and fill in value of m_ag_maxlevels.

fs/xfs/libxfs/xfs_bmap.c

@@ -3507,7 +3507,8 @@ xfs_bmap_longest_free_extent(
 		}
 	}
 
-	longest = xfs_alloc_longest_free_extent(mp, pag);
+	longest = xfs_alloc_longest_free_extent(mp, pag,
+						XFS_MIN_FREELIST_PAG(pag, mp));
 	if (*blen < longest)
 		*blen = longest;
 

fs/xfs/xfs_filestream.c

@@ -196,7 +196,8 @@ xfs_filestream_pick_ag(
 			goto next_ag;
 		}
 
-		longest = xfs_alloc_longest_free_extent(mp, pag);
+		longest = xfs_alloc_longest_free_extent(mp, pag,
+						XFS_MIN_FREELIST_PAG(pag, mp));
 		if (((minlen && longest >= minlen) ||
 		     (!minlen && pag->pagf_freeblks >= minfree)) &&
 		    (!pag->pagf_metadata || !(flags & XFS_PICK_USERDATA) ||