Re: [PATCH 15/21] mm: memmap_init: iterate over memblock regions rather that check each PFN

[Qian Cai <cai@lca.pw>]

> On Apr 12, 2020, at 3:48 PM, Mike Rapoport <rppt@kernel.org> wrote:
> 
> From: Baoquan He <bhe@redhat.com>
> 
> When called during boot the memmap_init_zone() function checks if each PFN
> is valid and actually belongs to the node being initialized using
> early_pfn_valid() and early_pfn_in_nid().
> 
> Each such check may cost up to O(log(n)) where n is the number of memory
> banks, so for large amount of memory overall time spent in early_pfn*()
> becomes substantial.
> 
> Since the information is anyway present in memblock, we can iterate over
> memblock memory regions in memmap_init() and only call memmap_init_zone()
> for PFN ranges that are know to be valid and in the appropriate node.
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
> mm/page_alloc.c | 26 ++++++++++++++++----------
> 1 file changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7f6a3081edb8..c43ce8709457 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5995,14 +5995,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> 		 * function.  They do not exist on hotplugged memory.
> 		 */
> 		if (context == MEMMAP_EARLY) {
> -			if (!early_pfn_valid(pfn)) {
> -				pfn = next_pfn(pfn);
> -				continue;
> -			}
> -			if (!early_pfn_in_nid(pfn, nid)) {
> -				pfn++;
> -				continue;
> -			}

This causes a compilation warning from Clang,

mm/page_alloc.c:5917:39: warning: unused function 'next_pfn' [-Wunused-function]
static inline __meminit unsigned long next_pfn(unsigned long pfn)

This should fix it,

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d469384c9ca7..b48336e20bdc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5912,23 +5912,6 @@ overlap_memmap_init(unsigned long zone, unsigned long *pfn)
 	return false;
 }
 
-#ifdef CONFIG_SPARSEMEM
-/* Skip PFNs that belong to non-present sections */
-static inline __meminit unsigned long next_pfn(unsigned long pfn)
-{
-	const unsigned long section_nr = pfn_to_section_nr(++pfn);
-
-	if (present_section_nr(section_nr))
-		return pfn;
-	return section_nr_to_pfn(next_present_section_nr(section_nr));
-}
-#else
-static inline __meminit unsigned long next_pfn(unsigned long pfn)
-{
-	return pfn++;
-}
-#endif
-
 /*
  * Initially all pages are reserved - free ones are freed
  * up by memblock_free_all() once the early boot process is

> 			if (overlap_memmap_init(zone, &pfn))
> 				continue;
> 			if (defer_init(nid, pfn, end_pfn))
> @@ -6118,9 +6110,23 @@ static void __meminit zone_init_free_lists(struct zone *zone)
> }
> 
> void __meminit __weak memmap_init(unsigned long size, int nid,
> -				  unsigned long zone, unsigned long start_pfn)
> +				  unsigned long zone,
> +				  unsigned long range_start_pfn)
> {
> -	memmap_init_zone(size, nid, zone, start_pfn, MEMMAP_EARLY, NULL);
> +	unsigned long start_pfn, end_pfn;
> +	unsigned long range_end_pfn = range_start_pfn + size;
> +	int i;
> +
> +	for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
> +		start_pfn = clamp(start_pfn, range_start_pfn, range_end_pfn);
> +		end_pfn = clamp(end_pfn, range_start_pfn, range_end_pfn);
> +
> +		if (end_pfn > start_pfn) {
> +			size = end_pfn - start_pfn;
> +			memmap_init_zone(size, nid, zone, start_pfn,
> +					 MEMMAP_EARLY, NULL);
> +		}
> +	}
> }
> 
> static int zone_batchsize(struct zone *zone)
> -- 
> 2.25.1
> 
>