David Hildenbrand <david@xxxxxxxxxx> writes: > On 27.06.24 02:54, Alistair Popple wrote: >> Currently to map a DAX page the DAX driver calls vmf_insert_pfn. This >> creates a special devmap PTE entry for the pfn but does not take a >> reference on the underlying struct page for the mapping. This is >> because DAX page refcounts are treated specially, as indicated by the >> presence of a devmap entry. >> To allow DAX page refcounts to be managed the same as normal page >> refcounts introduce dax_insert_pfn. This will take a reference on the >> underlying page much the same as vmf_insert_page, except it also >> permits upgrading an existing mapping to be writable if >> requested/possible. > > We have this comparably nasty vmf_insert_mixed() that FS dax abused to > insert into !VM_MIXED VMAs. Is that abuse now stopping and are there > maybe ways to get rid of vmf_insert_mixed()? It's not something I've looked at but quite possibly - there are a couple of other users of vmf_insert_mixed() that would need to be removed though. I just added this as dax_insert_pfn() because as an API it is really specific to the DAX use case. For example a more general API would likely pass a page/folio.
