Re: [PATCH] io_uring: don't allow IORING_SETUP_NO_MMAP rings on highmem pages

[Jeff Moyer <jmoyer@redhat.com>]

Jens Axboe <axboe@kernel.dk> writes:

> On 10/3/23 10:30 AM, Jeff Moyer wrote:
>> Hi, Jens,
>> 
[snip]
>> What do you think about throwing a printk_once in there that explains
>> the problem?  I'm worried that this will fail somewhat randomly, and it
>> may not be apparent to the user why.  We should also add documentation,
>> of course, and encourage developers to add fallbacks for this case.
>
> For both cases posted, it's rather more advanced use cases. And 32-bit
> isn't so prevalent anymore, thankfully. I was going to add to the man
> pages explaining this failure case. Not sure it's worth adding a printk
> for though.

I try not to make decisions based on how prevalent I think a particular
configuration is (mainly because I'm usually wrong).  Anyway, it's not a
big deal, I'm glad you gave it some thought.

> FWIW, once I got an arm32 vm setup, it fails everytime for me. Not sure
> how it'd do on 32-bit x86, similarly or more randomly. But yeah it's
> definitely at the mercy of how things are mapped.

...and potentially the load on the system.  Anyway, it's fine with me to
keep it as is.  We can always add a warning later if it ends up being a
problem.

Thanks!
Jeff