On Wed, Apr 10 2013 at 6:49pm -0400, Kent Overstreet <koverstreet@xxxxxxxxxx> wrote: > On Wed, Apr 10, 2013 at 04:54:40PM -0400, Mike Snitzer wrote: > > Hey, > > > > So DM core clearly needs to be more defensive about the possibility for > > a NULL return from bio_alloc_bioset() given I'm hitting a NULL pointer > > in DM's alloc_tio() because nr_iovecs=512. bio_alloc_bioset()'s call to > > bvec_alloc() only supports nr_iovecs up to BIO_MAX_PAGES (256). > > > > Seems bcache should be using bio_get_nr_vecs() or something else? > > > > But by using a bcache bucket size of 2MB, with the bcache staged in > > Jens' for-next, I've caused bcache to issue bios with nr_iovecs=512: > > Argh. Why is dm using bi_max_vecs instead of bi_vcnt? I could hack > around this in bcache but I think dm is doing the wrong thing here. But even bio_alloc_bioset() sets: bio->bi_max_vecs = nr_iovecs; And bio_clone_bioset() calls bio_alloc_bioset() with bio->bi_max_vecs. Similarly, __bio_clone() is using bi_max_vecs when cloning the bi_io_vec. So I'm missing why DM is doing the wrong thing. > Unless I've missed something in my testing (and bcache's BIO_MAX_PAGES > check isn't quite right, actually) bcache _is_ splitting its bios > whenever bio_segments(bio) > BIO_MAX_PAGES, it's only bi_max_vecs that's > potentially > BIO_MAX_PAGES. OK, but why drive bi_max_vecs larger than BIO_MAX_PAGES? -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
