Re: [Qemu-stable] [Nbd] [Qemu-devel] [PATCH] nbd: fix trim/discard commands with a length bigger than NBD_MAX_BUFFER_SIZE

[Paolo Bonzini]

On 10/05/2016 17:38, Alex Bligh wrote:
> > and are at the
> > mercy of however the kernel currently decides to split large requests).
> 
> I am surprised TRIM doesn't get broken up the same way READ and WRITE
> do.

The payload of TRIM has constant size, so it makes sense to do that.
The kernel then self-imposes a 2GB limit in blkdev_issue_discard.

On the other hand, READ and WRITE of size n can possibly require O(n)
memory.

Paolo