Re: [PATCH] softmmu/physmem: Improve guest memory allocation failure error message

[David Hildenbrand <david@redhat.com>]

On 23.08.21 11:23, Peter Maydell wrote:
> On Mon, 23 Aug 2021 at 09:40, David Hildenbrand <david@redhat.com> wrote:
>> Not opposed to printing the size, although I doubt that it will really
>> stop similar questions/problems getting raised.
> 
> The case that triggered this was somebody thinking
> -m took a byte count, so very likely that an error message
> saying "you tried to allocate 38TB" would have made their
> mistake clear in a way that just "allocation failed" did not.
> It also means that if a future user asks us for help then
> we can look at the error message and immediately tell them
> the problem, rather than going "hmm, what are all the possible
> ways that allocation might have failed" and going off down
> rabbitholes like VM overcommit settings...

We've had similar issues recently where Linux memory overcommit handling 
rejected the allocation -- and the user was well aware about the actual 
size. You won't be able to catch such reports, because people don't 
understand how Linux memory overcommit handling works or was configured.

"I have 3 GiB of free memory, why can't I create a 3 GiB VM". "I have 3 
GiB of RAM, why can't I create a 3 GiB VM even if it won't make use of 
all 3 GiB of memory".

Thus my comment, it will only stop very basic usage issues. And I agree 
that looking at the error *might* help. It didn't help for the cases I 
just described, because we need much more system information to make a 
guess what the user error actually is.

-- 
Thanks,

David / dhildenb