On Thu, Oct 14, 2021 at 06:56:51PM +0100, Joao Martins wrote: > > And I would document this relationship in the GUP side "This do/while > > is required because insert_pfn_pmd/pud() is used with compound pages > > smaller than the PUD/PMD size" so it isn't so confused with just > > "devmap" > > Also, it's not that PMDs span compound heads, it's that PMDs/PUDs use > just base pages. Compound pages/head in devmap are only introduced by > series and for device-dax only. I think it all makes sense, I just want to clarify what I mean by compound_head: compound_head(base_page) == base_page Ie a PMD consisting only of order 0 pages would have N 'compound_heads' within it even though nothing is a compound page. Which is relavent because the GUP algorithms act on the compound_head Jason
