On Fri, Sep 27, 2019 at 09:39:48AM -0700, Linus Torvalds wrote:
On Fri, Sep 27, 2019 at 5:17 AM Kirill A. Shutemov kirill@shutemov.name wrote:
Call it "walk_page_mapping()". And talk extensively about how the locking differs a lot from the usual "walk_page_vma()" things.
Walking mappings of a page is what rmap does. This code thas to be integrated there.
Well, that's very questionable.
The rmap code mainly does the "page -> virtual" mapping. One page at a time.
The page walker code does the "virtual -> pte" mapping. Always a whole range at a time.
Have you seen page_vma_mapped_walk()? I made it specifically for rmap code to cover cases when a THP is mapped with PTEs. To me it's not a big stretch to make it cover multiple pages too.
So I think conceptually, mm/memory.c and unmap_mapping_range() is closest but I don't think it's practical to share code.
And between mm/pagewalk.c and mm/rmap.c, I think the page walking has way more of actual practical code sharing, and is also conceptually closer because most of the code is about walking a range, not looking up the mapping of one page.
I guess it's matter of personal preferences, but page table walkers based on callback always felt wrong to me.