Re: [PATCH v2] powerpc/mm: Fix growth direction for hugepages mmaps with slice

[Aneesh Kumar K.V]

On 01/16/2018 10:18 PM, Christophe LEROY wrote:
> Le 16/01/2018 Ã 17:03, Aneesh Kumar K.V a ÃcritÂ:
> > Christophe Leroy <christophe.leroy@xxxxxx> writes:
> >
> > > An application running with libhugetlbfs fails to allocate
> > > additional pages to HEAP due to the hugemap being done
> > > inconditionally as topdown mapping:
> > >
> > > mmap(0x10080000, 1572864, PROT_READ|PROT_WRITE, 
> > > MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0) = 0x73e80000
> > > [...]
> > > mmap(0x74000000, 1048576, PROT_READ|PROT_WRITE, 
> > > MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0x180000) = 0x73d80000
> > > munmap(0x73d80000, 1048576)ÂÂÂÂÂÂÂÂÂÂÂÂ = 0
> > > [...]
> > > mmap(0x74000000, 1572864, PROT_READ|PROT_WRITE, 
> > > MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0x180000) = 0x73d00000
> > > munmap(0x73d00000, 1572864)ÂÂÂÂÂÂÂÂÂÂÂÂ = 0
> > > [...]
> > > mmap(0x74000000, 1572864, PROT_READ|PROT_WRITE, 
> > > MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0x180000) = 0x73d00000
> > > munmap(0x73d00000, 1572864)ÂÂÂÂÂÂÂÂÂÂÂÂ = 0
> > > [...]
> >
> > Can you explain the failure details above. I am not sure I understand
> > what to read from the above output.
>
> libhugetlbfs first requests an area of size 1.5Mbytes, at address 
> 0x10080000
> mmap() returns an area at address 0x73e80000
>
> Then libhugetlbfs requests an additional area on top of that, ie at 
> address 0x74000000, to expand the heap.
> But mmap() returns an area at address 0x73d80000, ie under the previous 
> area.


Can you share the test details?. Why does it not fail on book3s64? We 
use topdown search with book3s64.

> This is not the behaviour when using the generic (ie without mm_slices) 
> hugepages code, and this is not what libhugetlbfs expects for expending 
> the heap.

-aneesh