Re: [PATCH v2 4/4] mm/hugetl.c: warn out if expected count of huge pages adjustment is not achieved

[Mike Kravetz]

Cc: Michal

On 8/10/20 7:11 PM, Baoquan He wrote:
> Hi Mike,
> 
> On 07/23/20 at 11:21am, Mike Kravetz wrote:
>> On 7/23/20 2:11 AM, Baoquan He wrote:
> ...
>>>> But is kernel expected to warn for all such situations where the user
>>>> requested resources could not be allocated completely ? Otherwise, it
>>>> does not make sense to add an warning for just one such situation.
>>>
>>> It's not for just one such situation, we have already had one to warn
>>> out in mm/hugetlb.c, please check hugetlb_hstate_alloc_pages().
>>
>> Those are a little different in that they are warnings based on kernel
>> command line parameters.
>>
>>> As Mike said, in one time of persistent huge page number setting,
>>> comparing the old value with the new vlaue is good enough for customer
>>> to get the information. However, if customer want to detect and analyze
>>> previous setting failure, logging message will be helpful. So I think
>>> logging the failure or partial success makes sense.
>>
>> I can understand the argument against adding a new warning for this.
>> You could even argue that this condition has existed since the time
>> hugetlb was added to the kernel which was long ago.  And, nobody has
>> complained enough to add a warning.  I have even heard of a sysadmin
>> practice of asking for a ridiculously large amount of hugetlb pages
>> just so that the kernel will allocate as many as possible.  They do
>> not 'expect' to get the ridiculous amount they asked for.  In such
>> cases, this will be a new warning in their log.
>>
>> As mentioned in a previous e-mail, when one sets nr_hugepages by writing
>> to the sysfs or proc file, one needs to read the file to determine if the
>> number of requested pages were actually allocated.  Anyone who does not
>> do this is just asking for trouble.  Yet, I imagine that it may happen.
>>
>> To be honest, I do not see this log message as something that would be
>> helpful to end users.  Rather, I could see this as being useful to support
>> people.  Support always asks for system logs and this could point out a
>> possible issue with hugetlb usage.
>>
>> I do not feel strongly one way or another about adding the warning.  Since
>> it is fairly trivial and could help diagnose issues I am in favor of adding
>> it.  If people feel strongly that it should not be added, I am open to
>> those arguments.
> 
> Ping!
> 
> It's been a while, seems no objection to log the message. Do you
> consider accepting this patch or offering an Ack?
> 
> Thanks
> Baoquan

Adding Michal as he has had opinions about hugetlbfs log messages in the past.

-- 
Mike Kravetz