Re: [PATCH v3 2/5] mm: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()

[Jia He]

On 3/28/2018 1:17 AM, Daniel Vacek Wrote:
> On Mon, Mar 26, 2018 at 5:02 AM, Jia He <hejianet@xxxxxxxxx> wrote:
> > Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
> > where possible") optimized the loop in memmap_init_zone(). But there is
> > still some room for improvement. E.g. if pfn and pfn+1 are in the same
> > memblock region, we can simply pfn++ instead of doing the binary search
> > in memblock_next_valid_pfn. This patch only works when
> > CONFIG_HAVE_ARCH_PFN_VALID is enable.
> >
> > Signed-off-by: Jia He <jia.he@xxxxxxxxxxxxxxxx>
> > ---
> >   include/linux/memblock.h |  2 +-
> >   mm/memblock.c            | 73 +++++++++++++++++++++++++++++-------------------
> >   mm/page_alloc.c          |  3 +-
> >   3 files changed, 47 insertions(+), 31 deletions(-)
> >
> > diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> > index efbbe4b..a8fb2ab 100644
> > --- a/include/linux/memblock.h
> > +++ b/include/linux/memblock.h
> > @@ -204,7 +204,7 @@ void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
> >   #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
> >
> >   #ifdef CONFIG_HAVE_ARCH_PFN_VALID
> > -unsigned long memblock_next_valid_pfn(unsigned long pfn);
> > +unsigned long memblock_next_valid_pfn(unsigned long pfn, int *idx);
> >   #endif
> >
> >   /**
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index bea5a9c..06c1a08 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -1102,35 +1102,6 @@ void __init_memblock __next_mem_pfn_range(int *idx, int nid,
> >                  *out_nid = r->nid;
> >   }
> >
> > -#ifdef CONFIG_HAVE_ARCH_PFN_VALID
> > -unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
> > -{
> > -       struct memblock_type *type = &memblock.memory;
> > -       unsigned int right = type->cnt;
> > -       unsigned int mid, left = 0;
> > -       phys_addr_t addr = PFN_PHYS(++pfn);
> > -
> > -       do {
> > -               mid = (right + left) / 2;
> > -
> > -               if (addr < type->regions[mid].base)
> > -                       right = mid;
> > -               else if (addr >= (type->regions[mid].base +
> > -                                 type->regions[mid].size))
> > -                       left = mid + 1;
> > -               else {
> > -                       /* addr is within the region, so pfn is valid */
> > -                       return pfn;
> > -               }
> > -       } while (left < right);
> > -
> > -       if (right == type->cnt)
> > -               return -1UL;
> > -       else
> > -               return PHYS_PFN(type->regions[right].base);
> > -}
> > -#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
> > -
> >   /**
> >    * memblock_set_node - set node ID on memblock regions
> >    * @base: base of area to set node ID for
> > @@ -1162,6 +1133,50 @@ int __init_memblock memblock_set_node(phys_addr_t base, phys_addr_t size,
> >   }
> >   #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
> >
> > +#ifdef CONFIG_HAVE_ARCH_PFN_VALID
> > +unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn,
> > +                                                       int *last_idx)
> > +{
> > +       struct memblock_type *type = &memblock.memory;
> > +       unsigned int right = type->cnt;
> > +       unsigned int mid, left = 0;
> > +       unsigned long start_pfn, end_pfn;
> > +       phys_addr_t addr = PFN_PHYS(++pfn);
> > +
> > +       /* fast path, return pfh+1 if next pfn is in the same region */
> > +       if (*last_idx != -1) {
> > +               start_pfn = PFN_DOWN(type->regions[*last_idx].base);
> > +               end_pfn = PFN_DOWN(type->regions[*last_idx].base +
> > +                               type->regions[*last_idx].size);
> > +
> > +               if (pfn < end_pfn && pfn > start_pfn)
> > +                       return pfn;
> > +       }
> > +
> > +       /* slow path, do the binary searching */
> > +       do {
> > +               mid = (right + left) / 2;
> > +
> > +               if (addr < type->regions[mid].base)
> > +                       right = mid;
> > +               else if (addr >= (type->regions[mid].base +
> > +                                 type->regions[mid].size))
> > +                       left = mid + 1;
> > +               else {
> > +                       *last_idx = mid;
> > +                       return pfn;
> > +               }
> > +       } while (left < right);
> > +
> > +       if (right == type->cnt)
> > +               return -1UL;
> > +
> > +       *last_idx = right;
> > +
> > +       return PHYS_PFN(type->regions[*last_idx].base);
> > +}
> > +#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
> > +
> >   static phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
> >                                          phys_addr_t align, phys_addr_t start,
> >                                          phys_addr_t end, int nid, ulong flags)
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 2a967f7..0bb0274 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5459,6 +5459,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> >          unsigned long end_pfn = start_pfn + size;
> >          pg_data_t *pgdat = NODE_DATA(nid);
> >          unsigned long pfn;
> > +       int idx = -1;
> >          unsigned long nr_initialised = 0;
> >          struct page *page;
> >   #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
> > @@ -5490,7 +5491,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> >                           * end_pfn), such that we hit a valid pfn (or end_pfn)
> >                           * on our next iteration of the loop.
> >                           */
> > -                       pfn = memblock_next_valid_pfn(pfn) - 1;
> > +                       pfn = memblock_next_valid_pfn(pfn, &idx) - 1;
> >   #endif
> >                          continue;
> >                  }
> > --
> > 2.7.4
> So the function is only defined with CONFIG_HAVE_ARCH_PFN_VALID but
> it's called with CONFIG_HAVE_MEMBLOCK_NODE_MAP? The definition should
> likely depend on both options as the function really depends on both
> conditions. Otherwise it should be defined nop.
>
> --nX
Yes, thanks

--
Cheers,
Jia