Re: [PATCH 2/2] block: allow different-pgmap pages as separate bvecs in bio_add_page

[Naman Jain <namjain@linux.microsoft.com>]

On 4/7/2026 11:22 AM, Christoph Hellwig wrote:
>> -               if (!zone_device_pages_have_same_pgmap(bv->bv_page, page))
>> +               if (!zone_device_pages_compatible(bv->bv_page, page))
>>                          return 0;
>> -
>> -               if (bvec_try_merge_hw_page(q, bv, page, len, offset)) {
>> +               if (zone_device_pages_have_same_pgmap(bv->bv_page, page) &&
>> +                   bvec_try_merge_hw_page(q, bv, page, len, offset)) {
> 
> We still can't merge merge pages with different P2P pgmaps into the
> same request.
> 
> So the zone_device_pages_have_same_pgmap check should go into
> zone_device_pages_compatible and we need to stop building the bio
> as well in that case.

Ok, so rest all things same, from my last email, but my previous 
compatible function would look like this:

static inline bool zone_device_pages_compatible(const struct page *a,
                         const struct page *b)
{
     if (is_pci_p2pdma_page(a) || is_pci_p2pdma_page(b))
         return zone_device_pages_have_same_pgmap(a, b);
     return true;
}

This would prevent two P2PDMA pages from different pgmaps (different PCI 
devices) passing the compatible check and both get added to the bio.
Please correct me if that is not what you meant. I'll wait for a couple 
more days and send the next version with this, and we can review this again.

Thanks for your inputs.

Regards,
Naman