Peter Xu <peterx@xxxxxxxxxx> writes: > On Wed, Aug 17, 2022 at 02:41:19AM -0700, Nadav Amit wrote: >> 4. Having multiple TLB flushing infrastructures makes all of these >> discussions very complicated and unmaintainable. I need to convince myself >> in every occasion (including this one) whether calls to >> flush_tlb_batched_pending() and tlb_flush_pending() are needed or not. >> >> What I would like to have [3] is a single infrastructure that gets a >> “ticket” (generation when the batching started), the old PTE and the new PTE >> and checks whether a TLB flush is needed based on the arch behavior and the >> current TLB generation. If needed, it would update the “ticket” to the new >> generation. Andy wanted a ring for pending TLB flushes, but I think it is an >> overkill with more overhead and complexity than needed. >> >> But the current situation in which every TLB flush is a basis for long >> discussions and prone to bugs is impossible. >> >> I hope it helps. Let me know if you want me to revive the patch-set or other >> feedback. >> >> [1] https://lore.kernel.org/all/20220711034615.482895-5-21cnbao@xxxxxxxxx/ >> [2] https://lore.kernel.org/all/20220718120212.3180-13-namit@xxxxxxxxxx/ >> [3] https://lore.kernel.org/all/20210131001132.3368247-16-namit@xxxxxxxxxx/ > > I need more reading on tlb code and also [3] which looks useful to me. > It's definitely sad to make tlb flushing so complicated. It'll be great if > things can be sorted out someday. > > In this specific case, the only way to do safe tlb batching in my mind is: > > pte_offset_map_lock(); > arch_enter_lazy_mmu_mode(); > // If any pending tlb, do it now > if (mm_tlb_flush_pending()) > flush_tlb_range(vma, start, end); > else > flush_tlb_batched_pending(); I don't think we need the above 4 lines. Because we will flush TLB before we access the pages. Can you find any issue if we don't use the above 4 lines? Best Regards, Huang, Ying > loop { > ... > pte = ptep_get_and_clear(); > ... > if (pte_present()) > unmapped++; > ... > } > if (unmapped) > flush_tlb_range(walk->vma, start, end); > arch_leave_lazy_mmu_mode(); > pte_unmap_unlock(); > > I may miss something, but even if not it already doesn't look pretty. > > Thanks,
