Re: [v3,2/3] powerpc: get hugetlbpage handling more generic

[Christophe LEROY]

Le 24/11/2016 à 06:23, Scott Wood a écrit :
> On Wed, Sep 21, 2016 at 10:11:54AM +0200, Christophe Leroy wrote:
> > Today there are two implementations of hugetlbpages which are managed
> > by exclusive #ifdefs:
> > * FSL_BOOKE: several directory entries points to the same single hugepage
> > * BOOK3S: one upper level directory entry points to a table of hugepages
> >
> > In preparation of implementation of hugepage support on the 8xx, we
> > need a mix of the two above solutions, because the 8xx needs both cases
> > depending on the size of pages:
> > * In 4k page size mode, each PGD entry covers a 4M bytes area. It means
> > that 2 PGD entries will be necessary to cover an 8M hugepage while a
> > single PGD entry will cover 8x 512k hugepages.
> > * In 16 page size mode, each PGD entry covers a 64M bytes area. It means
> > that 8x 8M hugepages will be covered by one PGD entry and 64x 512k
> > hugepages will be covers by one PGD entry.
> >
> > This patch:
> > * removes #ifdefs in favor of if/else based on the range sizes
> > * merges the two huge_pte_alloc() functions as they are pretty similar
> > * merges the two hugetlbpage_init() functions as they are pretty similar
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> > Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>
> With this patch on e6500, running the hugetlb testsuite results in the
> system hanging in a storm of OOM killer invocations (I'll try to debug
> more deeply later).  This patch also changes the default hugepage size on
> FSL book3e from 4M to 16M.

Regarding the default hugepage size, it is a result of the merge of the 
two hugetlbpage_init().
Should I add an ifdef to get 4M on FSL book3e by default ?
What's the reason for selecting different hugepage sizes depending on 
the CPU ? I thought default size was selected based on what was existing.

What testsuite do you run exactly ?

Christophe