On Mon, Feb 02, 2026 at 09:07:10PM +0800, Lance Yang wrote: > > > Right, but if we can use full RCU for PT_RECLAIM, why can't we do so > > > unconditionally and not add overhead? > > > > The sync (IPI) is mainly needed for unshare (e.g. hugetlb) and collapse > > (khugepaged) paths, regardless of whether table free uses RCU, IIUC. > > In addition: We need the sync when we modify page tables (e.g. unshare, > collapse), not only when we free them. RCU can defer freeing but does > not prevent lockless walkers from seeing concurrent in-place > modifications, so we need the IPI to synchronize with those walkers > first.
Currently PT_RECLAIM=y has no IPI; are you saying that is broken? If not, then why do we need this at all?
