On 07.03.22 16:07, Oscar Salvador wrote:
> free_area_init_node() calls calculate_node_totalpages() and
> free_area_init_core(). The former to get node's {spanned,present}_pages,
> and the latter to calculate, among other things, how many pages per zone
> we spent on memmap_pages, which is used to substract zone's free pages.
>
> On memoryless-nodes, it is pointless to perform such a bunch of work, so
> make sure we skip the calculations when having a node or empty zone.
>
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Sorry, I'm late with review. My mailbox got flooded.
> ---
> mm/page_alloc.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 967085c1c78a..0b7d176a8990 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7312,6 +7312,10 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
> unsigned long realtotalpages = 0, totalpages = 0;
> enum zone_type i;
>
> + /* Skip calculation for memoryless nodes */
> + if (node_start_pfn == node_end_pfn)
> + goto no_pages;
> +
Just a NIT:
E.g., in zone_spanned_pages_in_node() we test for
!node_start_pfn && !node_end_pfn
In update_pgdat_span(), we set
node_start_pfn = node_end_pfn = 0;
when we find an empty node during memory unplug.
Therefore, I wonder if a helper "is_memoryless_node()" or "node_empty()"
might be reasonable, that just checks for either
!node_start_pfn && !node_end_pfn
or
node_start_pfn == node_end_pfn
> for (i = 0; i < MAX_NR_ZONES; i++) {
> struct zone *zone = pgdat->node_zones + i;
> unsigned long zone_start_pfn, zone_end_pfn;
> @@ -7344,6 +7348,7 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
> realtotalpages += real_size;
> }
>
> +no_pages:
> pgdat->node_spanned_pages = totalpages;
> pgdat->node_present_pages = realtotalpages;
> pr_debug("On node %d totalpages: %lu\n", pgdat->node_id, realtotalpages);
> @@ -7562,6 +7567,10 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
> size = zone->spanned_pages;
> freesize = zone->present_pages;
>
> + /* No pages? Nothing to calculate then. */
> + if (!size)
> + goto no_pages;
> +
> /*
> * Adjust freesize so that it accounts for how much memory
> * is used by this zone for memmap. This affects the watermark
> @@ -7597,6 +7606,7 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
> * when the bootmem allocator frees pages into the buddy system.
> * And all highmem pages will be managed by the buddy system.
> */
> +no_pages:
> zone_init_internals(zone, j, nid, freesize);
>
> if (!size)
We have another size check below. We essentially have right now:
"
if (!size)
goto no_pages;
[code]
no_pages:
zone_init_internals(zone, j, nid, freesize);
if (!size)
continue
[more code]
"
IMHO, it would be nicer to avoid the label/goto by just doing a:
"
if (!size) {
zone_init_internals(zone, j, nid, 0);
continue;
}
[code]
zone_init_internals(zone, j, nid, freesize);
[more code]
"
Or factoring out [code] into a separate function.
Anyhow, the change itself looks sane.
--
Thanks,
David / dhildenb
