xfs_scrub: request fewer bmaps when we can

In xfs_iterate_filemaps, we query the number of bmaps for a given file
that we're going to iterate, so feed that information to bmap so that
the kernel won't waste time allocating in-kernel memory unnecessarily.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/scrub/filemap.c b/scrub/filemap.c
index bdc6d8f90165defa1408a00649cdaf2d46d5b8ee..f92e962013c8785874ec807d6441f68cde1c352b 100644 (file)
--- a/scrub/filemap.c
+++ b/scrub/filemap.c
@@ -71,7 +71,6 @@ xfs_iterate_filemaps(
                map->bmv_length = ULLONG_MAX;
        else
                map->bmv_length = BTOBB(key->bm_length);
-       map->bmv_count = BMAP_NR;
        map->bmv_iflags = BMV_IF_NO_DMAPI_READ | BMV_IF_PREALLOC |
                          BMV_IF_NO_HOLES;
        switch (whichfork) {
@@ -97,6 +96,13 @@ xfs_iterate_filemaps(
                goto out;
        }
 
+       if (fsx.fsx_nextents == 0) {
+               moveon = true;
+               goto out;
+       }
+
+       map->bmv_count = min(fsx.fsx_nextents + 1, BMAP_NR);
+
        while ((error = ioctl(fd, XFS_IOC_GETBMAPX, map)) == 0) {
                for (i = 0, p = &map[i + 1]; i < map->bmv_entries; i++, p++) {
                        bmap.bm_offset = BBTOB(p->bmv_offset);