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

[Jia He]

On 3/28/2018 5:26 PM, Wei Yang Wrote:
> On Sun, Mar 25, 2018 at 08:02:16PM -0700, Jia He 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 */
>                               ^^^  pfn
Thanks
> > +	if (*last_idx != -1) {
> > +		start_pfn = PFN_DOWN(type->regions[*last_idx].base);
> To me, it should be PFN_UP().
hmm.., seems all the base of memory region is pfn aligned (0x10000 
aligned). So

PFN_UP is the same as PFN_DOWN here?
I got this logic from memblock_search_pfn_nid()

Cheers,
Jia

> > +		end_pfn = PFN_DOWN(type->regions[*last_idx].base +
> > +				type->regions[*last_idx].size);
> > +
> > +		if (pfn < end_pfn && pfn > start_pfn)
> Could be (pfn < end_pfn && pfn >= start_pfn)?
>
> pfn == start_pfn is also a valid address.
No, pfn=pfn+1 at the beginning, so 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*/
> The same comment as Daniel, you are moving the function out of
> CONFIG_HAVE_MEMBLOCK_NODE_MAP.
> > +
> > 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