xfs: reduce stack usage in xfs_iomap

xfs_iomap passes a xfs_bmbt_irec pointer to xfs_iomap_write_direct and
xfs_iomap_write_allocate to give them the results of our read-only
xfs_bmapi query.  Instead of allocating a new xfs_bmbt_irec on stack
for the next call to xfs_bmapi re use the one we got passed as it's not
used after this point.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

1 files changed, 28 insertions, 24 deletions

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 39ad46b3ed46..a0dbcaff911a 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -242,7 +242,7 @@ xfs_iomap_write_direct(
         xfs_off_t       offset,
         size_t          count,
         int             flags,
-        xfs_bmbt_irec_t *ret_imap,
+        xfs_bmbt_irec_t *imap,
         int             *nmaps)
 {
         xfs_mount_t     *mp = ip->i_mount;
@@ -256,7 +256,6 @@ xfs_iomap_write_direct(
         int             quota_flag;
         int             rt;
         xfs_trans_t     *tp;
-        xfs_bmbt_irec_t imap;
         xfs_bmap_free_t free_list;
         uint            qblocks, resblks, resrtextents;
         int             committed;
@@ -280,10 +279,10 @@ xfs_iomap_write_direct(
                 if (error)
                         goto error_out;
         } else {
-                if (*nmaps && (ret_imap->br_startblock == HOLESTARTBLOCK))
+                if (*nmaps && (imap->br_startblock == HOLESTARTBLOCK))
                         last_fsb = MIN(last_fsb, (xfs_fileoff_t)
-                                        ret_imap->br_blockcount +
-                                        ret_imap->br_startoff);
+                                        imap->br_blockcount +
+                                        imap->br_startoff);
         }
         count_fsb = last_fsb - offset_fsb;
         ASSERT(count_fsb > 0);
@@ -336,12 +335,15 @@ xfs_iomap_write_direct(
                 bmapi_flag |= XFS_BMAPI_PREALLOC;
 
         /*
-         * Issue the xfs_bmapi() call to allocate the blocks
+         * Issue the xfs_bmapi() call to allocate the blocks.
+         *
+         * From this point onwards we overwrite the imap pointer that the
+         * caller gave to us.
          */
         xfs_bmap_init(&free_list, &firstfsb);
         nimaps = 1;
         error = xfs_bmapi(tp, ip, offset_fsb, count_fsb, bmapi_flag,
-                &firstfsb, 0, &imap, &nimaps, &free_list);
+                &firstfsb, 0, imap, &nimaps, &free_list);
         if (error)
                 goto error0;
 
@@ -363,12 +365,11 @@ xfs_iomap_write_direct(
                 goto error_out;
         }
 
-        if (!(imap.br_startblock || XFS_IS_REALTIME_INODE(ip))) {
-                error = xfs_cmn_err_fsblock_zero(ip, &imap);
+        if (!(imap->br_startblock || XFS_IS_REALTIME_INODE(ip))) {
+                error = xfs_cmn_err_fsblock_zero(ip, imap);
                 goto error_out;
         }
 
-        *ret_imap = imap;
         *nmaps = 1;
         return 0;
 
@@ -542,7 +543,7 @@ xfs_iomap_write_allocate(
         xfs_inode_t     *ip,
         xfs_off_t       offset,
         size_t          count,
-        xfs_bmbt_irec_t *map,
+        xfs_bmbt_irec_t *imap,
         int             *retmap)
 {
         xfs_mount_t     *mp = ip->i_mount;
@@ -551,7 +552,6 @@ xfs_iomap_write_allocate(
         xfs_fsblock_t   first_block;
         xfs_bmap_free_t free_list;
         xfs_filblks_t   count_fsb;
-        xfs_bmbt_irec_t imap;
         xfs_trans_t     *tp;
         int             nimaps, committed;
         int             error = 0;
@@ -567,8 +567,8 @@ xfs_iomap_write_allocate(
                 return XFS_ERROR(error);
 
         offset_fsb = XFS_B_TO_FSBT(mp, offset);
-        count_fsb = map->br_blockcount;
-        map_start_fsb = map->br_startoff;
+        count_fsb = imap->br_blockcount;
+        map_start_fsb = imap->br_startoff;
 
         XFS_STATS_ADD(xs_xstrat_bytes, XFS_FSB_TO_B(mp, count_fsb));
 
@@ -647,10 +647,15 @@ xfs_iomap_write_allocate(
                                 }
                         }
 
-                        /* Go get the actual blocks */
+                        /*
+                         * Go get the actual blocks.
+                         *
+                         * From this point onwards we overwrite the imap
+                         * pointer that the caller gave to us.
+                         */
                         error = xfs_bmapi(tp, ip, map_start_fsb, count_fsb,
                                         XFS_BMAPI_WRITE, &first_block, 1,
-                                        &imap, &nimaps, &free_list);
+                                        imap, &nimaps, &free_list);
                         if (error)
                                 goto trans_cancel;
 
@@ -669,13 +674,12 @@ xfs_iomap_write_allocate(
                  * See if we were able to allocate an extent that
                  * covers at least part of the callers request
                  */
-                if (!(imap.br_startblock || XFS_IS_REALTIME_INODE(ip)))
-                        return xfs_cmn_err_fsblock_zero(ip, &imap);
+                if (!(imap->br_startblock || XFS_IS_REALTIME_INODE(ip)))
+                        return xfs_cmn_err_fsblock_zero(ip, imap);
 
-                if ((offset_fsb >= imap.br_startoff) &&
-                    (offset_fsb < (imap.br_startoff +
-                                   imap.br_blockcount))) {
-                        *map = imap;
+                if ((offset_fsb >= imap->br_startoff) &&
+                    (offset_fsb < (imap->br_startoff +
+                                   imap->br_blockcount))) {
                         *retmap = 1;
                         XFS_STATS_INC(xs_xstrat_quick);
                         return 0;
@@ -685,8 +689,8 @@ xfs_iomap_write_allocate(
                  * So far we have not mapped the requested part of the
                  * file, just surrounding data, try again.
                  */
-                count_fsb -= imap.br_blockcount;
-                map_start_fsb = imap.br_startoff + imap.br_blockcount;
+                count_fsb -= imap->br_blockcount;
+                map_start_fsb = imap->br_startoff + imap->br_blockcount;
         }
 
 trans_cancel: