dm-io calls bio_get_nr_vecs to get the maximum number of pages for a given device, then adds 1 to it and allocates bio with this size. The last vector is not used for i/o, it is used to hold information about the region this i/o belongs to. If bio_get_nr_vecs returned the maximum biovec size, dm-io attempts to allocate bio with one more vector and fails. Very likely this was the reason for bug https://bugzilla.redhat.com/show_bug.cgi?id=173153 (the bug was fixed with an userspace workaround preventing lvm from creating snapshots with chunksize >512k; after this patch is applied, that limit can be dropped) Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> --- drivers/md/dm-io.c | 2 ++ 1 file changed, 2 insertions(+) Index: linux-2.6.29-rc1-devel/drivers/md/dm-io.c =================================================================== --- linux-2.6.29-rc1-devel.orig/drivers/md/dm-io.c 2009-01-22 04:13:45.000000000 +0100 +++ linux-2.6.29-rc1-devel/drivers/md/dm-io.c 2009-01-22 04:14:13.000000000 +0100 @@ -292,6 +292,8 @@ static void do_region(int rw, unsigned r (PAGE_SIZE >> SECTOR_SHIFT)); num_bvecs = 1 + min_t(int, bio_get_nr_vecs(where->bdev), num_bvecs); + if (unlikely(num_bvecs > BIO_MAX_PAGES)) + num_bvecs = BIO_MAX_PAGES; bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, io->client->bios); bio->bi_sector = where->sector + (where->count - remaining); bio->bi_bdev = where->bdev; -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
