Cap maximum aggregate IO size

Commit 8542ef8 allowed optional IOs to be aggregated beyond
the specified aggregation limit.  Since the aggregation limit
was also used to enforce the maximum block size, setting
`zfs_vdev_aggregation_limit=16777216` could result in an
attempt to allocate an ABD larger than 16M.

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #6259
Closes #6270

diff --git a/module/zfs/vdev_queue.c b/module/zfs/vdev_queue.c
index 2439f2951c23f3cbb5596421ca2df58bba5cb167..6b3e8729159009749b49c702726a3bc4a0c7d10c 100644 (file)
--- a/module/zfs/vdev_queue.c
+++ b/module/zfs/vdev_queue.c
@@ -521,13 +521,14 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
        uint64_t maxgap = 0;
        uint64_t size;
        uint64_t limit;
+       int maxblocksize;
        boolean_t stretch = B_FALSE;
        avl_tree_t *t = vdev_queue_type_tree(vq, zio->io_type);
        enum zio_flag flags = zio->io_flags & ZIO_FLAG_AGG_INHERIT;
        abd_t *abd;
 
-       limit = MAX(MIN(zfs_vdev_aggregation_limit,
-           spa_maxblocksize(vq->vq_vdev->vdev_spa)), 0);
+       maxblocksize = spa_maxblocksize(vq->vq_vdev->vdev_spa);
+       limit = MAX(MIN(zfs_vdev_aggregation_limit, maxblocksize), 0);
 
        if (zio->io_flags & ZIO_FLAG_DONT_AGGREGATE || limit == 0)
                return (NULL);
@@ -584,6 +585,7 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
            (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
            (IO_SPAN(first, dio) <= limit ||
            (dio->io_flags & ZIO_FLAG_OPTIONAL)) &&
+           IO_SPAN(first, dio) <= maxblocksize &&
            IO_GAP(last, dio) <= maxgap) {
                last = dio;
                if (!(last->io_flags & ZIO_FLAG_OPTIONAL))
@@ -635,6 +637,7 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
                return (NULL);
 
        size = IO_SPAN(first, last);
+       ASSERT3U(size, <=, maxblocksize);
 
        abd = abd_alloc_for_io(size, B_TRUE);
        if (abd == NULL)