On 7/28/21 8:28 AM, Dan Williams wrote:
> On Wed, Jul 14, 2021 at 12:36 PM Joao Martins <joao.m.martins@xxxxxxxxxx> wrote:
>>
>> + /*
>> + * With compound page geometry and when struct pages are stored in ram
>> + * (!altmap) most tail pages are reused. Consequently, the amount of
>> + * unique struct pages to initialize is a lot smaller that the total
>> + * amount of struct pages being mapped.
>> + * See vmemmap_populate_compound_pages().
>> + */
>> + if (!altmap)
>> + nr_pages = min_t(unsigned long, nr_pages,
>
> What's the scenario where nr_pages is < 128? Shouldn't alignment
> already be guaranteed?
>
Oh yeah, that's right.
>> + 2 * (PAGE_SIZE/sizeof(struct page)));
>
>
>> +
>> __SetPageHead(page);
>>
>> for (i = 1; i < nr_pages; i++) {
>> @@ -6657,7 +6669,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
>> continue;
>>
>> memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
>> - pfns_per_compound);
>> + altmap, pfns_per_compound);
>
> This feels odd, memmap_init_compound() doesn't really care about
> altmap, what do you think about explicitly calculating the parameters
> that memmap_init_compound() needs and passing them in?
>
> Not a strong requirement to change, but take another look at let me know.
>
Yeah, memmap_init_compound() indeed doesn't care about @altmap itself -- but a previous
comment was to abstract this away in memmap_init_compound() given the mix of complexity in
memmap_init_zone_device() PAGE_SIZE geometry case and the compound case:
https://lore.kernel.org/linux-mm/CAPcyv4gtSqfmuAaX9cs63OvLkf-h4B_5fPiEnM9p9cqLZztXpg@xxxxxxxxxxxxxx/
Before this was called @ntails above and I hide that calculation in memmap_init_compound().
But I can move this back to the caller:
memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
(!altmap ? 2 * (PAGE_SIZE/sizeof(struct page))) : pfns_per_compound);
Or with another helper like:
#define compound_nr_pages(__altmap, __nr_pages) \
(!__altmap ? 2 * (PAGE_SIZE/sizeof(struct page))) : __nr_pages);
memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
compound_nr_pages(altmap, pfns_per_compound));
