On Mon 09-01-23 12:53:13, Suren Baghdasaryan wrote: > Protect VMA from concurrent page fault handler while collapsing a huge > page. Page fault handler needs a stable PMD to use PTL and relies on > per-VMA lock to prevent concurrent PMD changes. pmdp_collapse_flush(), > set_huge_pmd() and collapse_and_free_pmd() can modify a PMD, which will > not be detected by a page fault handler without proper locking. I am struggling with this changelog. Maybe because my recollection of the THP collapsing subtleties is weak. But aren't you just trying to say that the current #PF handling and THP collapsing need to be mutually exclusive currently so in order to keep that assumption you have mark the vma write locked? Also it is not really clear to me how that handles other vmas which can share the same thp? -- Michal Hocko SUSE Labs
