pnfs/blocklayout: return layouts on setattr

This speads up truncate-heavy workloads like fsx by multiple orders of
magnitude.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/blocklayout/blocklayout.c

@@ -799,7 +799,8 @@ static struct pnfs_layoutdriver_type blocklayout_type = {
 	.id				= LAYOUT_BLOCK_VOLUME,
 	.name				= "LAYOUT_BLOCK_VOLUME",
 	.owner				= THIS_MODULE,
-	.flags				= PNFS_READ_WHOLE_PAGE,
+	.flags				= PNFS_LAYOUTRET_ON_SETATTR |
+					  PNFS_READ_WHOLE_PAGE,
 	.read_pagelist			= bl_read_pagelist,
 	.write_pagelist			= bl_write_pagelist,
 	.alloc_layout_hdr		= bl_alloc_layout_hdr,