On Thu, Jul 21, 2016 at 11:22:32AM +0300, Saeed Mahameed wrote: > On Thu, Jul 21, 2016 at 8:15 AM, Alexei Starovoitov > <alexei.starovoi...@gmail.com> wrote: > > On Thu, Jul 21, 2016 at 01:20:02AM +0300, Saeed Mahameed wrote: > >> From: Hadar Hen Zion <had...@mellanox.com> > >> > >> Add support for query the minimum inline mode from the Firmware. > >> It is required for correct TX steering according to L3/L4 packet > >> headers. > >> > >> Each send queue (SQ) has inline mode that defines the minimal required > >> headers that needs to be copied into the SQ WQE. > >> The driver asks the Firmware for the wqe_inline_mode device capability > >> value. In case the device capability defined as "vport context" the > >> driver must check the reported min inline mode from the vport context > >> before creating its SQs. > >> > >> Signed-off-by: Hadar Hen Zion <had...@mellanox.com> > >> Signed-off-by: Saeed Mahameed <sae...@mellanox.com> > > ... > >> + int outlen = MLX5_ST_SZ_BYTES(query_nic_vport_context_out); > >> + u32 *out; > >> + > >> + out = mlx5_vzalloc(outlen); > >> + if (!out) > >> + return; > > > > Just discovered this... > > outlen is a small constant here, yet you want to try to vmalloc it? > > What is the point? > > There are 67 places in mlx5 where failed kmalloc is retried with > > vmalloc... was that path ever tested? > > The point is that there are a lot of places in the code that want to > allocate huge commands and mlx5_vzalloc is a nice black box that > provides the method to allocate such huge chunks of memory. > > Now sometimes people tend to reuse same pieces of code for code consistency. > > I don't see any harm from doing that.
There are several *_kvzalloc() helpers in the kernel. Their main purpose is to allocate large chunks of contigous memory. mlx5 driver just calls mlx5_vzalloc everywhere even when the size is known and it's small. There is a lot of harm in such 'consistency': . if we're under memory pressure and small size kmalloc fails, it will hurt the system if vmalloc somehow finds a free page for this small alloc . the memory returned by vmalloc is virtually contiguous, whereas the driver takes it and puts in all sort of hardware things. I'm not sure why I didn't blow up yet In general you should never call vmalloc with anything smaller than page size.
