Re: [PATCH v9 03/12] mm/hotplug: Prepare shrink_{zone, pgdat}_span for sub-section removal

[Wei Yang]

On Wed, Jun 05, 2019 at 02:58:04PM -0700, Dan Williams wrote:
>Sub-section hotplug support reduces the unit of operation of hotplug
>from section-sized-units (PAGES_PER_SECTION) to sub-section-sized units
>(PAGES_PER_SUBSECTION). Teach shrink_{zone,pgdat}_span() to consider
>PAGES_PER_SUBSECTION boundaries as the points where pfn_valid(), not
>valid_section(), can toggle.
>
>Cc: Michal Hocko <mhocko@xxxxxxxx>
>Cc: Vlastimil Babka <vbabka@xxxxxxx>
>Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
>Reviewed-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
>Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
>Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>---
> mm/memory_hotplug.c |   29 ++++++++---------------------
> 1 file changed, 8 insertions(+), 21 deletions(-)
>
>diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>index 7b963c2d3a0d..647859a1d119 100644
>--- a/mm/memory_hotplug.c
>+++ b/mm/memory_hotplug.c
>@@ -318,12 +318,8 @@ static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
> 				     unsigned long start_pfn,
> 				     unsigned long end_pfn)
> {
>-	struct mem_section *ms;
>-
>-	for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SECTION) {
>-		ms = __pfn_to_section(start_pfn);
>-
>-		if (unlikely(!valid_section(ms)))
>+	for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) {
>+		if (unlikely(!pfn_valid(start_pfn)))
> 			continue;

Hmm, we change the granularity of valid section from SECTION to SUBSECTION.
But we didn't change the granularity of node id and zone information.

For example, we found the node id of a pfn mismatch, we can skip the whole
section instead of a subsection.

Maybe this is not a big deal.

> 
> 		if (unlikely(pfn_to_nid(start_pfn) != nid))
>@@ -343,15 +339,12 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
> 				    unsigned long start_pfn,
> 				    unsigned long end_pfn)
> {
>-	struct mem_section *ms;
> 	unsigned long pfn;
> 
> 	/* pfn is the end pfn of a memory section. */
> 	pfn = end_pfn - 1;
>-	for (; pfn >= start_pfn; pfn -= PAGES_PER_SECTION) {
>-		ms = __pfn_to_section(pfn);
>-
>-		if (unlikely(!valid_section(ms)))
>+	for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) {
>+		if (unlikely(!pfn_valid(pfn)))
> 			continue;
> 
> 		if (unlikely(pfn_to_nid(pfn) != nid))
>@@ -373,7 +366,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> 	unsigned long z = zone_end_pfn(zone); /* zone_end_pfn namespace clash */
> 	unsigned long zone_end_pfn = z;
> 	unsigned long pfn;
>-	struct mem_section *ms;
> 	int nid = zone_to_nid(zone);
> 
> 	zone_span_writelock(zone);
>@@ -410,10 +402,8 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> 	 * it check the zone has only hole or not.
> 	 */
> 	pfn = zone_start_pfn;
>-	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SECTION) {
>-		ms = __pfn_to_section(pfn);
>-
>-		if (unlikely(!valid_section(ms)))
>+	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
>+		if (unlikely(!pfn_valid(pfn)))
> 			continue;
> 
> 		if (page_zone(pfn_to_page(pfn)) != zone)
>@@ -441,7 +431,6 @@ static void shrink_pgdat_span(struct pglist_data *pgdat,
> 	unsigned long p = pgdat_end_pfn(pgdat); /* pgdat_end_pfn namespace clash */
> 	unsigned long pgdat_end_pfn = p;
> 	unsigned long pfn;
>-	struct mem_section *ms;
> 	int nid = pgdat->node_id;
> 
> 	if (pgdat_start_pfn == start_pfn) {
>@@ -478,10 +467,8 @@ static void shrink_pgdat_span(struct pglist_data *pgdat,
> 	 * has only hole or not.
> 	 */
> 	pfn = pgdat_start_pfn;
>-	for (; pfn < pgdat_end_pfn; pfn += PAGES_PER_SECTION) {
>-		ms = __pfn_to_section(pfn);
>-
>-		if (unlikely(!valid_section(ms)))
>+	for (; pfn < pgdat_end_pfn; pfn += PAGES_PER_SUBSECTION) {
>+		if (unlikely(!pfn_valid(pfn)))
> 			continue;
> 
> 		if (pfn_to_nid(pfn) != nid)
>
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-- 
Wei Yang
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