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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 8/20/21 6:40 PM, Igor Mammedov wrote:
> On Fri, 20 Aug 2021 18:00:26 +0200
> Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
> 
>> On 8/20/21 5:53 PM, David Hildenbrand wrote:
>>> On 20.08.21 17:52, Philippe Mathieu-Daudé wrote:  
>>>> When Linux refuses to overcommit a seriously wild allocation we get:
>>>>
>>>>    $ qemu-system-i386 -m 40000000
>>>>    qemu-system-i386: cannot set up guest memory 'pc.ram': Cannot
>>>> allocate memory
>>>>
>>>> Slighly improve the error message, displaying the memory size
>>>> requested (in case the user didn't expect unspecified memory size
>>>> unit is in MiB):
>>>>
>>>>    $ qemu-system-i386 -m 40000000
>>>>    qemu-system-i386: Cannot set up 38.1 TiB of guest memory 'pc.ram':
>>>> Cannot allocate memory
>>>>
>>>> Reported-by: Bin Meng <bmeng.cn@gmail.com>
>>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>> ---
>>>>   softmmu/physmem.c | 4 +++-
>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
>>>> index 2e18947598e..2f300a9e79b 100644
>>>> --- a/softmmu/physmem.c
>>>> +++ b/softmmu/physmem.c
>>>> @@ -1982,8 +1982,10 @@ static void ram_block_add(RAMBlock *new_block,
>>>> Error **errp)
>>>>                                                    
>>>> &new_block->mr->align,
>>>>                                                     shared, noreserve);
>>>>               if (!new_block->host) {
>>>> +                g_autofree char *size_s =
>>>> size_to_str(new_block->max_length);
>>>>                   error_setg_errno(errp, errno,
>>>> -                                 "cannot set up guest memory '%s'",
>>>> +                                 "Cannot set up %s of guest memory
>>>> '%s'",
>>>> +                                 size_s,
>>>>                                    memory_region_name(new_block->mr));
>>>>                   qemu_mutex_unlock_ramlist();
>>>>                   return;
>>>>  
>>>
>>> IIRC, ram blocks might not necessarily be used for guest memory ... or
>>> is my memory wrong?  
>>
>> No clue, this error message was already here.
> 
> it's not only guest RAM, adding size here is marginal improvement,
> (it won't help much since it's not exact match to CLI which may use suffixes for sizes)

The suffixed size is already converted at this point:

  qemu-system-i386 -m 2T
  qemu-system-i386: Cannot set up 2 TiB of guest memory 'pc.ram': Cannot
allocate memory

I agree however the size displayed might be less than the size passed
to the '-m' argument.

Anyhow I still see the size displayed in the error message as an
useful hint:

$ qemu-system-i386 -m 64000
qemu-system-i386: cannot set up guest memory 'pc.ram': Cannot allocate
memory

VS:

$ qemu-system-i386 -m 64000
qemu-system-i386: Cannot set up 62.5 GiB of guest memory 'pc.ram':
Cannot allocate memory

> 
>>
>> No problem to change s/guest/block/ although.
>>
>