Re: [PATCH 33/36] autonuma: powerpc port

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2012-08-23 at 08:01 +1000, Benjamin Herrenschmidt wrote:
> On Wed, 2012-08-22 at 16:59 +0200, Andrea Arcangeli wrote:
> > From: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
> > 
> >     * PMD flaging is not required in powerpc since large pages
> >       are tracked in ptes.
> >     * Yet to be tested with large pages
> >     * This is an initial patch that partially works
> >     * knuma_scand and numa hinting page faults works
> >     * Page migration is yet to be observed/verified
> > 
> > Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
> > Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> 
> I don't like this.

What I mean here is that it's fine as a proof of concept ;-) I don't
like it being in a series aimed at upstream...

We can try to flush out the issues, but as it is, the patch isn't
upstreamable imho.

As for finding PTE bits, I have a few ideas we need to discuss, but
nothing simple I'm afraid.

Cheers,
Ben.

> ---
> >  arch/powerpc/include/asm/pgtable.h        |   48 ++++++++++++++++++++++++++++-
> >  arch/powerpc/include/asm/pte-hash64-64k.h |    4 ++-
> >  arch/powerpc/mm/numa.c                    |    3 +-
> >  mm/autonuma.c                             |    2 +-
> >  4 files changed, 53 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> > index 2e0e411..5f03079 100644
> > --- a/arch/powerpc/include/asm/pgtable.h
> > +++ b/arch/powerpc/include/asm/pgtable.h
> > @@ -33,10 +33,56 @@ static inline int pte_dirty(pte_t pte)		{ return pte_val(pte) & _PAGE_DIRTY; }
> >  static inline int pte_young(pte_t pte)		{ return pte_val(pte) & _PAGE_ACCESSED; }
> >  static inline int pte_file(pte_t pte)		{ return pte_val(pte) & _PAGE_FILE; }
> >  static inline int pte_special(pte_t pte)	{ return pte_val(pte) & _PAGE_SPECIAL; }
> > -static inline int pte_present(pte_t pte)	{ return pte_val(pte) & _PAGE_PRESENT; }
> > +static inline int pte_present(pte_t pte)	{ return pte_val(pte) &
> > +							(_PAGE_PRESENT|_PAGE_NUMA_PTE); }
> 
> Is this absolutely necessary ? (testing two bits). It somewhat changes
> the semantics of "pte_present" which I don't really like.
> 
> >  static inline int pte_none(pte_t pte)		{ return (pte_val(pte) & ~_PTE_NONE_MASK) == 0; }
> >  static inline pgprot_t pte_pgprot(pte_t pte)	{ return __pgprot(pte_val(pte) & PAGE_PROT_BITS); }
> >  
> > +#ifdef CONFIG_AUTONUMA
> > +static inline int pte_numa(pte_t pte)
> > +{
> > +       return (pte_val(pte) &
> > +               (_PAGE_NUMA_PTE|_PAGE_PRESENT)) == _PAGE_NUMA_PTE;
> > +}
> > +
> > +#endif
> 
> Why the ifdef and not anywhere else ?
> 
> > +static inline pte_t pte_mknonnuma(pte_t pte)
> > +{
> > +       pte_val(pte) &= ~_PAGE_NUMA_PTE;
> > +       pte_val(pte) |= (_PAGE_PRESENT|_PAGE_ACCESSED);
> > +
> > +       return pte;
> > +}
> > +
> > +static inline pte_t pte_mknuma(pte_t pte)
> > +{
> > +       pte_val(pte) |= _PAGE_NUMA_PTE;
> > +       pte_val(pte) &= ~_PAGE_PRESENT;
> > +       return pte;
> > +}
> > +
> > +static inline int pmd_numa(pmd_t pmd)
> > +{
> > +       /* PMD tracking not implemented */
> > +       return 0;
> > +}
> > +
> > +static inline pmd_t pmd_mknonnuma(pmd_t pmd)
> > +{
> > +	BUG();
> > +	return pmd;
> > +}
> > +
> > +static inline pmd_t pmd_mknuma(pmd_t pmd)
> > +{
> > +	BUG();
> > +	return pmd;
> > +}
> > +
> > +/* No pmd flags on powerpc */
> > +#define set_pmd_at(mm, addr, pmdp, pmd)  do { } while (0)
> > +
> >  /* Conversion functions: convert a page and protection to a page entry,
> >   * and a page entry and page directory to the page they refer to.
> >   *
> > diff --git a/arch/powerpc/include/asm/pte-hash64-64k.h b/arch/powerpc/include/asm/pte-hash64-64k.h
> > index 59247e8..f7e1468 100644
> > --- a/arch/powerpc/include/asm/pte-hash64-64k.h
> > +++ b/arch/powerpc/include/asm/pte-hash64-64k.h
> > @@ -7,6 +7,8 @@
> >  #define _PAGE_COMBO	0x10000000 /* this is a combo 4k page */
> >  #define _PAGE_4K_PFN	0x20000000 /* PFN is for a single 4k page */
> >  
> > +#define _PAGE_NUMA_PTE 0x40000000 /* Adjust PTE_RPN_SHIFT below */
> > +
> >  /* For 64K page, we don't have a separate _PAGE_HASHPTE bit. Instead,
> >   * we set that to be the whole sub-bits mask. The C code will only
> >   * test this, so a multi-bit mask will work. For combo pages, this
> > @@ -36,7 +38,7 @@
> >   * That gives us a max RPN of 34 bits, which means a max of 50 bits
> >   * of addressable physical space, or 46 bits for the special 4k PFNs.
> >   */
> > -#define PTE_RPN_SHIFT	(30)
> > +#define PTE_RPN_SHIFT	(31)
> 
> I'm concerned. We are already running short on RPN bits. We can't spare
> more. If you absolutely need a PTE bit, we'll need to explore ways to
> free some, but just reducing the RPN isn't an option.
> 
> Think of what happens if PTE_4K_PFN is set...
> 
> Also you conveniently avoided all the other pte-*.h variants meaning you
> broke the build for everything except ppc64 with 64k pages.
> 
> >  #ifndef __ASSEMBLY__
> >  
> > diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> > index 39b1597..80af41e 100644
> > --- a/arch/powerpc/mm/numa.c
> > +++ b/arch/powerpc/mm/numa.c
> > @@ -22,6 +22,7 @@
> >  #include <linux/pfn.h>
> >  #include <linux/cpuset.h>
> >  #include <linux/node.h>
> > +#include <linux/page_autonuma.h>
> >  #include <asm/sparsemem.h>
> >  #include <asm/prom.h>
> >  #include <asm/smp.h>
> > @@ -1045,7 +1046,7 @@ void __init do_init_bootmem(void)
> >  		 * all reserved areas marked.
> >  		 */
> >  		NODE_DATA(nid) = careful_zallocation(nid,
> > -					sizeof(struct pglist_data),
> > +					autonuma_pglist_data_size(),
> >  					SMP_CACHE_BYTES, end_pfn);
> >  
> >    		dbg("node %d\n", nid);
> > diff --git a/mm/autonuma.c b/mm/autonuma.c
> > index ada6c57..a4da3f3 100644
> > --- a/mm/autonuma.c
> > +++ b/mm/autonuma.c
> > @@ -25,7 +25,7 @@ unsigned long autonuma_flags __read_mostly =
> >  #ifdef CONFIG_AUTONUMA_DEFAULT_ENABLED
> >  	|(1<<AUTONUMA_ENABLED_FLAG)
> >  #endif
> > -	|(1<<AUTONUMA_SCAN_PMD_FLAG);
> > +	|(0<<AUTONUMA_SCAN_PMD_FLAG);
> 
> That changes the default accross all architectures, is that ok vs.
> Andrea ?
> 
> Cheers,
> Ben.
> 
> >  static DEFINE_MUTEX(knumad_mm_mutex);
> >  
> 


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