Subject: Re: [RFC] powerpc/hugetlb: Add warning message when gpage allocation request fails

From: Anshuman Khandual <[email-masked]>
Date: Tue, 15 Sep 2015 09:13:36 +0530

On 09/14/2015 09:54 PM, Nishanth Aravamudan wrote:
> On 14.09.2015 [18:59:25 +0530], Aneesh Kumar K.V wrote:
>> > Anshuman Khandual <[email-masked]> writes:
>> > 
>>> > > When a 16GB huge page is requested on POWER platform through kernel command
>>> > > line interface, it silently fails because of the lack of any gigantic pages
>>> > > on the system which the platform should have communicated through 16GB memory
>>> > > blocks in the device tree during boot time. For example
>>> > >
>>> > > [    0.480940] HugeTLB registered 16 GB page size, pre-allocated 0 pages
>>> > > [    0.480945] HugeTLB registered 16 MB page size, pre-allocated 16 pages
>>> > >
>>> > > This adds a warning message during alloc_bootmem_huge_page request both on
>>> > > book3e and book3s powerpc platforms. After this change
>>> > >
>>> > > [    0.000000] Gigantic HugeTLB page not available
>>> > > [    0.473417] HugeTLB registered 16 GB page size, pre-allocated 0 pages
>>> > > [    0.473423] HugeTLB registered 16 MB page size, pre-allocated 16 pages
>> > 
>> > 
>> > That info is already part of the second line isn't it ? ie
>> > 
>> > [    0.473417] HugeTLB registered 16 GB page size, pre-allocated 0 pages
>> > 
>> > pre-allocated 0 pages indicate we didn't allocate anything. So why do we
>> > need to add more details fo kernel output ?
> Agreed, the '0 pages' message indicates we failed to pre-allocate any
> pages. The 'pre-allocate' messages are specifically about the kernel
> command-line requests for hugepages.
> 
> Not sure I understand the motivation for this?

The motivation was just to add a cause to the failure of allocation
of requested 16G huge pages. I think "pre-allocated 0 pages" does
not hint about the cause of the failure.