[PATCH] nvme-sysfs: display max_hw_sectors_kb without requiring namespaces

[Abhishek Bapat]

On Thu, Oct 17, 2024 at 9:40 AM Keith Busch <kbusch at kernel.org> wrote:
>
> On Wed, Oct 16, 2024 at 09:31:08PM +0000, Abhishek Bapat wrote:
> > max_hw_sectors based on DMA optimized limitation") introduced a
> > limitation on the value of max_hw_sectors_kb, restricting it to 128KiB
> > (MDTS = 5). This restricion was implemented to mitigate lockups
> > encountered in high-core count AMD servers.
>
> There are other limits that can constrain transfer sizes below the
> device's MDTS. For example, the driver can only preallocate so much
> space for DMA and SGL descriptors, so 8MB is the current max transfer
> sizes the driver can support, and a device's MDTS can be much bigger
> than that.
>
> Anyway, yeah, I guess having a controller generic way to export this
> sounds like a good idea, but I wonder if the nvme driver is the right
> place to do it. The request_queue has all the limits you need to know
> about, but these are only exported if a gendisk is attached to it.
> Maybe we can create a queue subdirectory to the char dev too.

Are you suggesting that all the files from the queue subdirectory should
be included in the char dev (/sys/class/nvme/nvmeX/queue/)? Or that
just the max_hw_sectors_kb value should be shared within the queue
subdirectory? And if not the nvme driver, where else can this be done
from?