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

From: Michael Ellerman <[email-masked]>
Date: Tue, 15 Sep 2015 09:55:38 +1000

On Mon, 2015-09-14 at 09:24 -0700, 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.

Yeah, that's sufficient. We don't need more boot-time log spam.

All the info you need should be in /sys/kernel/mm anyway. If it's not, then
that is something we should fix.

cheers