Reduce size of zfs_sb_t: allocate z_hold_mtx separately

zfs_sb_t has grown to the point where using kmem_zalloc() for allocations
is triggering the 32k warning threshold.

We can't safely convert this entire allocation to use vmem_alloc() instead
of kmem_alloc() because the backing_dev_info structure is embedded here.
It depends on the bit_waitqueue() function which won't behave properly
when given a virtual address.

Instead, use vmem_alloc() to allocate the z_hold_mtx array separately.

Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Chris Dunlop <[email protected]>
Closes #3178

1 files changed, 6 insertions, 0 deletions

diff --git a/module/zfs/zfs_vfsops.c b/module/zfs/zfs_vfsops.c
index e98f4bf6a..41a1c4d88 100644
--- a/module/zfs/zfs_vfsops.c
+++ b/module/zfs/zfs_vfsops.c
@@ -776,6 +776,9 @@ zfs_sb_create(const char *osname, zfs_sb_t **zsbp)
 	rrw_init(&zsb->z_teardown_lock, B_FALSE);
 	rw_init(&zsb->z_teardown_inactive_lock, NULL, RW_DEFAULT, NULL);
 	rw_init(&zsb->z_fuid_lock, NULL, RW_DEFAULT, NULL);
+
+	zsb->z_hold_mtx = vmem_zalloc(sizeof (kmutex_t) * ZFS_OBJ_MTX_SZ,
+	    KM_SLEEP);
 	for (i = 0; i != ZFS_OBJ_MTX_SZ; i++)
 		mutex_init(&zsb->z_hold_mtx[i], NULL, MUTEX_DEFAULT, NULL);
 
@@ -789,6 +792,8 @@ zfs_sb_create(const char *osname, zfs_sb_t **zsbp)
 out:
 	dmu_objset_disown(os, zsb);
 	*zsbp = NULL;
+
+	vmem_free(zsb->z_hold_mtx, sizeof (kmutex_t) * ZFS_OBJ_MTX_SZ);
 	kmem_free(zsb, sizeof (zfs_sb_t));
 	return (error);
 }
@@ -892,6 +897,7 @@ zfs_sb_free(zfs_sb_t *zsb)
 	rw_destroy(&zsb->z_fuid_lock);
 	for (i = 0; i != ZFS_OBJ_MTX_SZ; i++)
 		mutex_destroy(&zsb->z_hold_mtx[i]);
+	vmem_free(zsb->z_hold_mtx, sizeof (kmutex_t) * ZFS_OBJ_MTX_SZ);
 	mutex_destroy(&zsb->z_ctldir_lock);
 	avl_destroy(&zsb->z_ctldir_snaps);
 	kmem_free(zsb, sizeof (zfs_sb_t));